HISTORICAL DYNAMICS OF ARTEMISIA

TRIDENTATA NUTT. IN

SOUTHERN BRITISH COLUMBIA

Kenneth B. Cawker

B.A. (Hons.) University of Toronto, 1969

M.A. University of Toronto, 1971

A THESIS SUBMITTED IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

IN THE DEPARTMENT

OF

GEOGRAPHY

@ Kenneth B. Cawker 1978

SIMON FRASER UNIVERSITY

July 1978

All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. Name: Kenneth B. Cawker

Degree: Doctor of Philosophy (Geography)

Title of Thesis : Historical Dyna~~licsof Arterlii sia- tridentata- --. Nutt. in Southern British Columbia .

Exami ning Colnmi t tee :

Chai rman: ,'.I. L. Carkerl

Senior Supcrvi sor

- J.D. Sauer

External Examiner Uni vers ity of Cal iforui a. Los Angelcs PARTIAL COPYRIGHT LICENSE

I hereby grant to Simon Fraser University the right to lend my thesis or dissertation (the title of which is shown below) to users of the Simon Fraser University Librafy, and to make partial or single copies only for such users or in response to a request from the 1ibrary of any other university, or other educational institution, on its own behalf or for one of its users. I further agree that permission for multiple copying of this thesis for scholarly purposes may be granted by me or the Dean of Graduate Studies. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

Title of Thesis/Di ssertation :

Historical Dynamics of Big Sagebrush, Artemisia

tridentata Nutt. in Southern British Columbia.

Author : - - (signature)

K.R. wer (name)

July 12, 1978

-- (date) Tb-i s stuCIy exmi j~espo2rtl a-tii.r c;e,rl:,rrai;!:y :nrJ pbg'l~ti on hiis tory of Artemisia --triaentata ktt. in southern Eri.ci;sh h?rihia. This shrub is s ccn;mon ra~~cjelandweed, often occurririg -i~denss? st,ands md caus-ir::; reduced forage yl:elds by competition \:i th desirable grass species.

Although obviously well adapted La 1-11? en; irocni2n-k of the study area at thc present tin?, the species \;as appawnt?y much 'less c~ii~mndcrir.3 the middle and 'late nineteenth century, and its increased ab[indance s.i:~::e that time has b~ens ttributed to ov3rgrazi ng by domes tic l i ves tock. , . Over the course of tihe last centui,y, it is be! jc.v.ed to i:ilv:. .n;s~!:i;~:-ld the 'climax grasslandsi of the arrs and replaced thein with a 'sayebl-rir;!i disc1 imax' . In 5p.i %e of ~xtensiwstudy, the exact mc-chanisin by which overgrazing induced this cha.nge has rberriained obscure, as have the major physical and biot-ic controls on the s~ecies'range 2nd densi t,y.

This study was umkrtaken in ai? attempt to deter-niine

seed1 i ngs by the ss t;bi is!;e3 Artwi.- ., .. -. si --- a tri delitat,?- .. . pop1xi or;. Peri nd5

j f .i of good recruitment are correlated with periods of low fall and high winter temperatures, with high spring temperatures, with low preci pi - tation and adequate moisture reserves in the fall, and with years of high mois ture defi ci t, a1 though early summer rain may be necessary to prevent seedling dessication. Grass competition appears to operate mainly through the restriction of bare mi neral soi 1 germination mi cro- sites, without which seedling mortality is high. Such sites may be created by grazing disturbance, rodent activity, or prolonged drought. Although this mechanism may provide a link between overgrazing and Artemisia tridentata invasion, the availability of suitable microsi tes does not appear to have been an important limiting factor in the field during the past ten years, and the natural availabi 1i ty of such micro- sites in the absence of grazing appears adequate to support a substantial population of Artemisia tridentata in the area. A1 lelopathic suppression by mature plants may serve to strengthen the modal age structure which derives initially from climatic variation, but is considered unimportant as a determinant of long-term population change. Fire is capable of destroying estab1 ished stands of Artemisia tridentata, and re-establishment of the species on burned areas is re1 atively s1ow. Sera1 stages may i nvol ve Artemi sia frigi da or Artemi sia tripartita, which are more fire tolerant than Artemisia tridentata. Popul ation his tory was exami ned from documentary sources and the local pol len record. The documentary sources i ndicate an increasing abundance of shrubby Artemisia through the latter part of the nineteenth century, but both documentary and pollen evidence point to Artemisia triparti ta as the chief increaser prior to about 1900, followed by an i v inciaease in the abundance of krtmisia-. - triden:a?,a.------. The pol lei1 yec~rd indicates that the early settl emerk period war chara::tcri.ed by unusual ly

achieved in pre-settlement times in the abse~ceof ovc~grazingby domestic 2 ivestock. Local fire his tory is reconstrlxtcd usi ns documentary records and que!iti tative estinlatrts of the ab~rrc'anceof fino c!?arcoal in the pol 1en samples. Fire frequency appmrs te have i 2crznsed duri ng the early settleme~itperiod, and to have declined after tho early decades sf this century. The pollen and charcoal records indicate a statistical relatiorisbi p betwccn fi re occurrence arid the abundance an4 species comp~sitim of the Artemisiz popula tioi-i throughout tile perZo3 of record.

It is concluded that the low Artemisia tridentata popuiation during the early settlement peri~dwas due to frequent range fire at that time, and that the recent increase in -Rrtemisia - tridentata -- abundance in this area is due chiefly to fire suppression rather thac to overgrazing. I wish pa?-tic~t1 arly to thank those peop! e who coti-lributed to this study: Dr. T. C. Brayshaw of the Provincial r,crharf urn in

Victoria, and Dr. F. Fisher, who kindly opened their herbaria to me; and R. Davis for prcviding unpublished climatic d2.b frortl the field area. The assistarlce of G. Nznson, t. Stevenson &rid others cn several coring expeditions was greatly appreciated.

Thanks are also due to the fdcu1t.y 3rd stud~ntsuf the

Geography Department of Simon Fraser bnivers-ity far their interest, encouragcnent and stimulatf on, and particularly to Y. C. Kc1 lrnan for his suggestions and cri ticisn. Finally, I wish to thank my wifes Ivana, for her assistarm in the field and her tolerance and encouragement at home. TABLE OF CONTEN-is Page ABSTRACT ...... iii

LIST OF -CABLES ...... xi LIST OF FIGURES ...... xi i i

CHAPTER

I . Introduction ...... I1 . Traditions of Historical Biog2ography ...... 1I I . PI ant Popul a t'on Irynarr~irs : The Quest'ioi.1 of Scz!e ...... IV . The Choice of Species ...... V . Research Strategy ...... THESTUDYAREA ...... 10 X . Geof oyy and Geonorphof ogy ...... 10 I1 . Climate ...... 14 111 . Climatic History ...... 11 IV . So-ils ...... 23 V . Nat-ural Vegetation ...... 25 Vi. Settlement and Land Use ...... 32 PREVIOUS RESEARCH ON ARTEF.?ISIA TRIDENTPPTA ...... 35 . I . .axonomy ...... 35 A . Artemisia trident_a.s ...... 35 B . Other Species of Ar'teini sia ...... 37 li . Life Cycle and Phenoloyy ...... 39 III . Seedling Ecology ...... 39 A. Germ-inaticn ...... 40 B . (Zrr3klth at>d SurvSva1 ...... 4: CHAPTER Page 111 IV . Envf ronniental Controls of Densi t.y and Range ... A . Climnte ...... B . Soils ...... C . Grazing and Competition Effects ...... D . Fire ...... V . Allelapathy ...... VI . Population Dynamics and Age Structure ...... VII . Paleobotanical Studies ......

I V DEMOGRAPHIC CHARACTERISTICS OF ...... AKTEMISIA ...--.1-RIUENTATA: THE CONTROLS ON PRESENT ABl:NDANCE .... I . Introduction ...... I1 . Reseirch Strategy ...... IT1 . Population Age Structure in --Artcnisia ...... tridentata- ...... A . Method ...... B . Results and Discussion ...... C . Derivation of the Establishmetit Record ... IV . Inter-speci fic Conlpeti tion and Grazing Effects ...... A . Introducticn ...... B . An Experimental Study of Grass Competition ...... (a) Method ...... (b) Resul ts and Discussion ...... C . Field Studies of Grazing Effects ...... D . Other Contrcls cn Microsi te Av2ilabi7i'ij? . . V . Direct Clinatic Controls on !lecre\itment Success ...... A . Tntroduction ...... B . Derivat.ion of the Independ~ntVat.iaDles ... C . The Structure of the Analysfs ...... D . Results and Discassion ...... E . I~terpretation ...... F . Vdlidation ...... G . Summry ......

viii Page VI . The Effects of Intra-specific Competi tion ...... 103 A . Evidence of Xntra-speci fic Cc!-rl;~etitior? i 11 the Age Structure Sainple ...... 104 B . A Test For P.ut o-allelopaihy ...... 1-10 C . Discussion ...... 113 SIX . Tne Ef fccts cf Fire ...... 114 A . Methcd ...... 114 B . Results and Discussion ...... 116 VIII.Suam;ry ...... 124 DOCUbIENTARY RECORDS ...... 127

I I . Docui~er~taiyMaterials : Ovwgrmf 2.: and the Artemisia . Popul?tion ...... 130 I11 . Documentary Records: Fire History ...... 142 IV . Photographic; Evidcncn ...... 152

THE PALEOECOLOSICAL RECORD ...... 167 I . In.troducti,on ...... 167 A . Techniques of Pollen Analysis ...... 168 B . Data Representation ...... 170 C . Sampling Cesign ...... 172 II . ---.Artemisia Pollen Taxonomy ...... 175 I11 . The Moderu Pollen Rain: Surface Safiple Data ... 178 A . L.ocal Effects ...... 178 B . Regional Effects ...... 179 IV . Fossil Pollen Spectra: Richtrr Marsh ...... 186 A . Site DescriptSon and Nethods ...... 186 B . Results ...... 186 (a) Pol 1en Strati cjraphy ...... 187

(b) ?he .....Arternisia -. .. Record: Pollen Size Ddta ...... 191 (c) Thc Charcoal Record ...... 195 C . Analysis and Tni.erp..e.ation ...... 195 CHAPTER Page v I (a) General Comments ...... 195 (b) The Charcoal Record : Correl a ti orrs with Ar'iemi.. si a Pol 1en D? tj ...... 197 Fossil Pollen Spectra 11: Twin Lake ...... 200 A . Site and Ekthod ...... 'LOO (a) Lcrcaticin and Say?; it:g ...... 2013 (b) Dating ...... 201 (c) Pol 1en Kepresentat.ion ...... 207 8 . ResuS ts and Discussion ...... 209 C . The Charcoal Kec~rd ...... 255 U . Summary ...... 224 VI . Fossil Pollen Spectra 111: Mahoney Lake ...... *...... 225 A . Site and Method ...... 225 (a) Location and Sampling ...... 225 (b) Dating ...... 226 6 . Results dnd Discussicm ...... 227 6 . The Charcoal Record ...... 234 D . Summary ...... 238 VII . Suniwary and Discussion ...... 238 VI I SUMMARY AND COI\ICI.USIONS ...... 246

BIBLIOGRAPHY ...... 254 APPENDICES ...... 269 I-' 0

d.2 0 7 ct 3 0 C ow C') a 0 " -'. IDD 'U -h -r -1. TABLE Description Page IV. 12 Test of Differential Fire Se:ls.itivit.y in ------Artcmisia -- tridet~tataand other Artemisia species ... Forest Age Structure and Inferred Fire Frequency ...... 'J .2 Forest and Grassland Fire, fron 1914 to 1963 .....

VI. 1 --Artevi s r'z- Pol l en Si zc Data From Fio6e;-n Ref ei-etm M6 teri a1 ...... Ric!~ter ivlarsh--Poll en S; ze Frequencies by Policn Sjze ...... Richter Marsh--Gorrel ation Coefficient5 (Spearxmn' s ) Betweell Charcoal Val ues drld -Arten?;--- s.- i - a- F3i1 en indices ...... Twic Lake: Varve Counts ...... k?ultlple Regre5sion--Charcoal Content as a Funct.i on of Selected Parameters, Twi n Lake,All Samples ......

Kul.tipl z Rcgressi cn----Charcml C;:,.rtcn.t 33 a Functf on of Selected Parawt~rs, 'fwi r-: Lake, pre-1860 ......

Correl atl; ons Between Mean ----Artenlisia Pol 1 en Size and Abundance of Artemisia--- Pollen Size Fracti ons ...... LIST OF FIGURES

FIGURE Description Page

2.1 TheStudyArea ...... 11 2.2 Climatic Normals from Selected Stations ...... 15 2.3 Moisture Balance Data for the Study Area ...... 18 2.4 Tree Ring Data from Yoho Park. B.C...... 20

2.5 Penticton Tree Ring Index as a Function of Actual Evapotranspiration ...... 21 Naramata Tree Ring Index Smoothed by Five Year Moving Average ...... 22

Recent Water Deficit Fluctuations at Penticton. B.C. Smoothed by Seven Year Moving Average ...... 24

Distribution of Artemisia tridentata in Southern British Columbia ...... 38 Artemisia tridentata Sample Sites ...... 61

Schematic Diagram of 'Random Walk' Sampling Design ...... 62

Age Structure of Artemisia tridentata by Sample Site ...... 65

Regional Age Structure of Artemisia tridentata. as Mean of Sites A to J ...... 67 Regional Age Structure with Fitted Trend Line; Negative Exponential Model I ...... 70 Regional Age Structure with Fitted Trend Line; Power Function Model I1 ...... 71 Grass Competition Experiment ...... 75 Total Weight of Artemisia tridentata Standing Biomass as a Function of pH ofSurfaceSoi1 ...... 78 xiii Pescri pti on Page

Artem?sSa triiit?ntata ngs on ------.- -- .- -- Seedl i Bare H-i net-a1 Soi i Sites ...... 80

-P.rten!i-- .- - sjd- .-. -"ir.icilentdt.s. - -- - .. ...- - - .- -.. .- Seedl ings in a Patch of &re Kixrzi Sail at Site G ...... 83

Effect cf Drought o:: Artenisia-. trgidentata Recruj tn?&>t 85 -e--- ......

Artemisih --tridetitatc 3t Site D ...... 98 Predicted tieci.ui tmnt Ind2x Values, Model I, 3s a Fbr,ction of Elevdtion , ...... 100 Predicted Recruitment Index Values, t4ode1 I!, as a Fr:n:ticn of Elevztion . , ...... 'LO1 Frcdic t2d Kecrui tiw~tI~ciex ties, Model Ila, as a Function of klevation ...... 102

Densi try Dependence in A. --tridet!tata: - - Densf ty and Freqtier~cyas Function of Censity of Older Plants , . . jC6 Test foi- Dt?nsity kpendent Rccr~!?imnt in ---Arternisia --trid~ntata ...... 108 Es tab1 i shtiient Frequency as a Functir~r~of the Age of Older Plants in the Same Quadrat ...... 109 Burnt Sample Site M at Richter Mountain ...... 115 Schematic Diagram at Sampling Design at Site M . . . . 117 Sample Site H in the sumner of 1974 ...... 121 Sa!:tp!e Site H after Fire in 1975 ...... 121

-Artmisia 3t.ri~a.-ti +a Resprsuti ng After Fire at Site H ...... 122

-Chrysoths.mnus nauseosus- Resprotiti~g After Fire at Site H ...... 522

Artemisis pa-.trin~rti ta- - Resprouted ar;d in Blosm Four Years After Fire at Site M ...... 123 The Pacific Norxhwest ...... 131 Cawston, near Mouth of Blind Man's Creek, Looking Ikst in 1919 and 1975 ...... 140 FIGUE Description Pap

5.3.5.4 C~wston.Ar...... iemisia - -tridentata... -.- Cover of 3, 919 Replaced by Orchards ...... 241 5.5 Ratio of kres of Grassland Fire to Far-est Fix. fmii 1914 ...... 149 5 .6 Cawston. Con:pc?rison Views from 1929 to 1915 ..... 153

5.9-5.10 Mouth of the Ashqola River. Looking Northeast. 1919 and 1975 155

5.31-5.12 Sim;lkamcsn Valley, rear Caston. Looking East ...... 156 5.13.5.14 Richter Lake. Looking West...... 1.57 5.15-5.16 Ri ehter Lake, Looki ng Southeast O~er Kilpoola ad Klue Lakes ...... 155 5.1.7.5.18 Tw-!ri Lake. Looking Southwest. 1917 and 1575 ..... 159 5.19.5.20 Twin Lake. Look'ng Lies t ...... 160 5.21.5.22 Twin Lake. Looking Northwest ...... I61 5.23.5.24 Martron Val 1ey . Looking South ...... 162 5.25.5.26 Marron Valley. Exact Location Unknown ...... 163 6.1 Pollen Sanlpie Sites and Transects ...... 174 6.2 Size Frequency Distributions of three Artexisia-Species ...... 177 6.3 Change in Artemi s5a Pol 1en Percentage w xh 0:'stance from the Edge of an Isolated Stand of Artemisia tridentata ...... 180

6.4-6.5 Visual Abundance Transect Station 20. West of Kers!neos ...... 182 6.6 Visua! Abundance Transect Sta.tion 63. Site E of the Age Structure Saiiqle ...... 133

6.7 .Artemisia .. pptridentata . Abundance from Visual Estimates and --.Artelnisia pol len Percentilge and Mean Pollen Size Along the Sirnil ka~ezi~Vai?ey .... 185 FIGURE Descri ptio~ Page

6.8 Richter Marsh, Reld tive Pc'l len Diagrar~i ...... 188

6.9 Richter Marsh, Loss on iyni tion and Pollen Concentraticn Data ...... i89 Richter Marsh - ArtemisSa Detail ...... 192 'Frigid Finger' Core f;-orti Twin Lake ...... 202 Pol lei1 Core frorn Twj n Lake, Showing 1mi na ted Str!!ctirre . . . .*...... 203 Twi n L ake--cedimcntation Curve Determined from Varve Counts ...... 205

Twin Lake--Total P9! len Conr;entratTon as a Futxtion of loss on ignition ...... 208 Twin Lake--Relative Pollen Diagram ...... 210 Twi n Lake---Grai ns per Gram Organic ...... 2 11

Twi r~ Lake--Artemisia---- - Poi l en Detai 1 ...... 2'13 Twin Lake--Chitrcoal Percentage as a Functim of Loss on Ignition ...... 216 Twin Lake--Residuals froli; Regrssion of Charcoal on Loss on Ignition, as an Index of Grassland Fire Occurrence ...... 218 Twin Lake--Simple Correlations Between Charcoal Percentagz and Poll~n Concentra.tions for Selected Taxa ...... 220 Mahoney Lake--Relative Pollen Diagram ...... 228 Mahoney Lake--Pol 1en Concentration as Grains per Gram Total Dry biei yht ...... 229

Mahoney Lake--Loss on Ignition as 3 Function of Charcoal Percentage ...... 230 Mahoney Lake--Total Pel 1en Concentration as a Function of L~sson Ignition ...... 23 1

Mahoney Lake--Artmisia--.- Pollen Detai 1 ...... 233

Mahoney L.a ke--Mean -Artcaii- --- sia-- . Pol 1 en Size as a Function of Charcoal Pzrcentage ...... 235 N TI- P. P. r3.i N

C C;I 'r- c . -+) IS R,T L . CHAPTER I

INTRODUCTION

I. Introductim -.

The study of vegetation change, through time at 2 partictilar location, has long represented a traditior! in biogeography Cistifict from the chorological tradition of vegetaticn class

wi th-in those pwulations, for a change in the size or distrib!;tion of or;e of ti-me popu'lat.i;rr)s is, hy definition, a chail~c?7:: 4be vegetation of which itffcrmr a part, In the hi~rzrchyWxi~ indiv.idb2.l pliint to species populatiot; to vegetation assmIJlage: it -is ti12 in;".erbrtleding, reprcductive popuiatinn which is the rvttiuaa1 fcas of t i~ron~logical

of th2 vugeta t i on assmb'agr is uncer tzi:) (21ezson , 1925; Anderson, population chancje. In this, it has beer, necessary to t.reat popu'iztion processes at severzl different time scales. Some ~f the prcb'icn:~ and cpportuni tics which vesu; t from such treatment are cons-itiered below.

In treatirq the dyrmics of any spccicis pci!ulztic;i, it is necessary to consider the range of ternporsl scales st which the VJ.I-*~~US processes which control species abuvjance operate. At on$ end of this temporal cant.: nuum there is abundant cjenl ogi cal cvider:ce of !aiye changes in the ioca? &bundance of part.ic~7arspecies oqer .long periods of time. Such changes have often !xm intcr.p,'et~das cvidenca of envi rormei3t.al , p3rt-icul arly cl ima tic, chanae. At i:he otker end of the conti nuim many p?,p!)?i~tiior,sconvey ;in 'iir!!.)l,?sSi~nof circitt st~bil i ty , and are often assrrmeci to be in s state of equi 1 ibr4?ini bii il; the 1~~7 envjr.onrnent. Th-is -~~T.?~Esslot1 may Le psr~,lc!.~lcr!; strwg feu. ypulat'rons in which i ndiv iduals ax relatively 1o:ig-'.! ived, a!!.'; 'cumover rates slow.

Although there has beer) sane rrxent researci~intc the nature and . .. stab31 i ty of ti1 i s eq!r I 1 ibrj urn, the mjoi*it: ~f s I;u~i es have treated annual or short-liwd pcrcrinial popu:atioi:s (Sarukh+.n i-ir;:l Hitrpw, 1973;

Sat-ukhan, 1974), ar:d rclat'ively fa.: have c!eal t w'it:h "Ltle i!loi.e difficult prubl tins posed h:~ 1 loncj-1 ivctl perennia'l s. A1 though wny usef~li nsf ghts hdve come frorn s:rci~ short-.ter.tn stud

Because of this slow process, there nust be a s trcicg suslji:cim that the apparent stability of many perennial populations, and of the cornmur~itiescomposed of these populations, is only re1 atiw to the cornparati vel y short time periods over wiii ch thsy are uscral 1y observed,

Increasi ng the pericd of observation may reveal nlore extens iue pop1a- tion fluctuations, as the dmping effects of the response ?a3 becorne 7;:s~ effective. The effective response time wi 11 vary wi th the 1ongevi t,y of the species involved, but may he very long. It has been estimated th3t once ciispl aced, the equi 1 i bri um between pcjp!ti 3 [.ion ii~rimvi ~01\1i!eili.!:lay require up to one thcusand yeai.5 to stabjl ize (Martin, 1953; Katts,

1373). Population changes at s~ichsca.les cannot be cbserved directly, an3 Wztts (1973) h?.s suggested the term "paleo-ppul %tion ecology" for studies which treat populat.ions at such scales, dlid has argued the value of palynoloyy as a relevant methodology. tkweuer5 a1 tbugh tbe methods employed in such studies may be distinctive enough tc warrsnt this nomenclatui-e, the oSjoctives of such research are ndt fundamentally different fro111 those of studies which focus on a inrich shorter time scale, Both aye conceri-ied with .the causes and m~chanismof change or stability i rz poplation sSze. They merely focus rjr! different scales in the teirrporal conti num a1 ong which these changes are expressed. The pss~jbi'i S ty of population chancy a.t extended tirw scales fias irnpi i cati cns ?or both the C~PYG:ocjj cdl ard chruno! ogi ca! tr:j.di ti ons in biocjeo~raplyr. The possibi 1i "l;: of i~nperce$yecic!-~+.~:ge~ v;hpti;(?r directional or mewly raridom, must ca'i 1 i nt9 q~lestionti;2 valid i.ty of mappi rig vegetaticn as though it were entire1y static. The prohleins for histor

'disturbance equilibrium' which bears I i ttle resemhl ant? to the cl inlatic cl irnax. The dangers fcr pal eoenv-i~~onmerita!i nterpretzti on of species aburdance data are obvious . Similarly, this instability and slow respnse nust make it difficult to deterxi !ie the rean equilibrium character cf the vegetation in any area. While early successional stages and other forms of rapid change may be read-i ly recognized, thz 1ater cuccess-ional stages and slow equilibriuril acijustn;ents may be inore diffic!rlt to detect, and necessitate spectllirti ve extrapolation of short-tern1 trends. Exact knowledge of the theoretical, cl imx vegrta ti orr in equil ibrium wi th the environment, is thus impossible, as is an exact picture of the relationship of the present species pop!jliti 3ns to that thewet-iia1 climax. For rmrly t.ypes of ir,;lestigat7:cri, this prcblm is i-;?dl Sut relativeiy mi nor, and i t hzs recei veci 1 i tt'ie c?ti:crrti~r~'!:I i:cnseqi;ence.

It takes on greater i!:~pcr.t;nx:.e -in cssss where th:: mvi roi-amt. is known to be relatively unstaS12 in conip.~r.isont.9 ti;c respofise t-ime of the species, and in stutf-i~sat' i-scent veyetatian change, l:r, which the expect& changes are efteen slrbtl e, 3rd the stcte of ';,tie !~riclist~!r3ed,

'bench mark ' vcgeta tioi-i relatively urtknown. Ekfol-e it: f s possible to speak of vegetdtion chanp, it is rtecwszrj to know ~oi!~i>thi~gof mean sizes and densities of the ccmpotxnt species popul~tiow,and of the range of variation ahout that mean pos; tion. Ogiy \/.lien s~c?'bench mark' d8ta 2re available can the degree of rjo~u!at;i:crn ctiaily he accurately assessed, and the causes of such rhar,ge prcpu.1.v considered.

The species Art.en;l:sia tridenta- ta Fk-kt., or hiy ssgcbi-ush, provides an example of a poplrlatior! of long--1ived plants grwi 1.g in the relatively unstable environmer~tof the semi -desert grasslands of westerr! Ncrth

America, for whirh silch bench indri: data zr.3 iti~d~c.~~t3ijjknown. It is a woody shrub.. or snmf 'i tree which dominates, 3;. '-L3n;wesent time, large areas of dry grassiand from southern British Coiumb.ia to Utah and

Nevada. Research on the 1or~g-t.erm popillatior~ dilnarni cs I:-? this partic- ular species was s~ygesteb ini tia! ly by an appiir.~!ntc~i"w~'lict. within the exis ti rig 1i temture.

Many ~cologistssubscribe to the view of \+xver and Clsments

(1938) that over much of -its present rariye, i~cludifigtb.5 lisi!eys of southern British Coi tmbia, -ArtemS. -- - -- . -. -- sia. -triderlt?-- .- .. ------ta. -. - 5ac :.cct?ct'ly invaded, and has bec.onle ti72 dam-inatit member of a sacjehr~sl-idisc? imax, induced prirnari ly by overgrazi ng. This view was restated by Cl ervet:t.f and

Clernerrts (].!%I). They note that under the ,i nf 1 wnce of ovci-g1-az-i ng ,

----Artewisia tride~tataexpanded its range from a few relict arex ". . . zntil in a little 123rP than two decades .it becam the agparevt climx, with the air of having a:ways been in possession of the west.':

Otheys disacree? a.nd some workers have argued that the species is a normal consti twnt of much ~f i-he dry grasslat-d where it is DGA; coiisi dcrec! to be emtic (Daubenmi re, 1990; tl 1 i suri, I960 1. 1'h.i s \ti ew is strengthened by the few pollen diagrams available from these areas, which appear to indicate subst.antial --A~~tpnif . -. s -- ia - --tridentata --- -.- - - populsticts in the pre-settlement period, and which shot? little evidence of any rece~t mjcr i ncresse in population size (Bright, 1956; P,r,der:

1976). Resol uti on of' thi :; conf 'I 'i ct. hss beer; hl:~-!p~r;.d ny i naduquate know1 edge of ~i~vironxental cuntro; s on thc popul aii~rr, and of the ~~~~~~e of these gi4asslanas prior to European settlewnt.

These probl ems concerni ng the h:'s tor5 cal iiy!!aiiiics o 7 the

---Arternisia tridentata pop1rl2ticn have close para7 lei ,; in other areas of western North herica , where recent changes i n pop~l at-ion size, often as jnvasions of grassland by woody shrubs or trees, have teen widely dociizented (!?cave;* and Clements, 1938; Hur;yf-l\.ey, i258; Cooper, 1960;

Hastings and Turner, 1965). In spite of much research, the causes and extent of these zppau'ent changes rema-i r: obscr.~re. Ov~rgrazing by ciornesti c 1 i vt.5 tcck, changes in thz rodent population due to predator control programs, cl-in!atic change, and changes in the frequeficy 6-F burning have a11 kcen invoked to e;!.;;lai n ?'tie i nvasicns, which a'i 1 seerll (1965) have reviewed thcse changes and the pos~.ibiecdust-.s fcin an area in Arizona, but they note in sumary: The more one reviews the ever;ts . . . the more p-lrsistei~tly the problen obtrudes cf their relation to ccrl ier vcgeLative history. To what extent is this cbb and fiow of plant ljfe partof the norm1 rhythrn of the desert region? TG what. extent is it a unsque event?"

in the valleys of British ColmSia, vinich is the fxus of th-is research.

V. -Research Strat~gyI-

Thc following material has beer! divided irlto fivc chciplr-zrs and a conclus3on. The first two of these treat the gecgraph icnl setting within which the research wzs contilrcted (Cha~terJi) and thz existing li tcrature os7 ----Artmisia -- trid2n- taLd (fh3pttr 111 !. The rewai ni rig material has been treated in three chapters, dealing with the denogrsphy of, and present. environmental controls upsn, the exis tjt.13 popu'l ation

(Chapter IV), docu!nentary rzcords deal i rcj wi th the dynarni cs of the population over the last century (Chapter V) , and the record cf popu- lation history provided by pcifen analysis (Chapter \!I).

Detailed aim iysi; s of populatf c.11 hiskry req~liil.5 know1 cdge, not. only of the factual history of the populstiotl invoived, but also of the envi ronniental factors hhich control the populat ;cn ai the i~resmttimz, and whose a1 teration in the past may hav-l been responsible for whatwer population changes r;w observed. One cf tk adv:tntages c.f txat'ing a single spec'les is thc opportunity to treat both tiif mcc!trl? and h-isto~ical aspects of the pcyul~ticnden~ography in som depth, witbin the cor,Lext of a single i!?t;egrated research design. With this cgi;!c:s th-. oppor:~;nity to compare res~!!ts t:t sevcrai time scales arid ~<:vF-;~sof telvporal integration. if it is difficult to extrapoia-1.e fror:i short-term observations of the present populatiun to long--term results of pi-+ cesses which nic?y he too ciow or infrequent to bc observed effect.i,ilely in a direct nariner, it. mqy be possible, as \dnt.ts (1973) has tlentbt~s~trateci, to observe the;? prczesses i rid-irectly , .~hr~~lghthe S'oszi! rmxd or ~Y'UKI documentar-y sources, A1 ihoiyh obsewatiim of th~modcien population mag be necessc.iry to interpret the in;.@suits of historical

~ecessarily fragmentary, and the concl usiws corrcs;xbndi ngly tentative.

Under such circumstances, it is important that many different data sources he tapped, 3rd tile results cowared, while firldl jtilqcwnt is rcserved until all of thz evidence is in. THE STUCY AREA

The study area choseti (F-iq. 2.1) lies in the soutf-tertl parts of the Okanzgan and Simi?kameen Valleys of soirthorn British Columbia, in at: area bounded roughly by the settle1 ients of Hed'lej~, Oscyoos, and

Per~ticton. It represents ore of tdii ~iajor3reas 07 seigebr~shcovx within the province, the other being the 1o.w- vl:l!t?ys of ;he Pli cola and Thompson Rivers, and the Val ley of the iraser, Frcm about Lytton, t~ near Willisnls Lake. In addition, a small population exists i~the

Princetcn area, and anctheu. has beer! reported from near Midsray (Rauermari, 1884 ) .

I. Gcol ogy and Seowrph01 oyy

The geology of the area is cotnplex. The oldest known rocks, in the vicii~.ityof Richter Pass, are th~i~ghtt.~ be of Carboiiifwctis age.

Much of the area f s a comp'lex mosaic of Triassic sediments ~;hichhave been extensively altered by intrusi\~esot Jurassic age. To thc east, the area is bounded by the granites of the St;ur:~ap coc~::plex(Jurassic ?) ar~dto the west by the Cretaceous and Tert'iary sed-i!lient,s of the Princetoll

Basin (G .S.C., 1940). The area appears to have been redxed to a pene- plain by the early Tertiary. Sniaii areas of Oligocene or Eocetx fresh water sediiwnts may be found, as it1 the White Lake ccal basin. Ifuch of

1CI Fkure 2.1. The study are shortly theiwf ter, 2nd thi5 was followed by extensive up1 ift in Miocene or P.iiocc!ie tiw. As a result of this uplift and rejuvenation, the lar~el'rivers hirvc cut far below the levei of the original plain, which remai !IS as a bi ssec tcd plateau surface, traceab?e o:ll y as accordant ridge tqs az abcut 6,000 feet (1,830 in). Sow arcas, such as the 0kr;ltrd~anRange, south of the Simi'lkamrzen Rive?, :9se to elevations of

7,033 and 8,009 feet (2,100 .- 2,400 ni), ap;:re:~liji as a result of dtffei-ential ~lplift or erosicm. The valley bottoeis presently lie at elevct;ons o+ beween 300 cnJ 1800 feet (275 -- 553 il;j. The mosi recent glaciation in the area is thought to correiate wi tti the advaxe of W-iscoxi n ice on the rest. rjf the continent.

E\fide;lcc of r.~!-! i~ryl xiation; ;s largely absent (Nasrili th, 1962).

An ice tkickncss of at least 2,009 feet (2,400 m) has kiln suggested

(Nasmi th, I%?),a1 tholrgk the area ljes relatively e;ose to the ice margin in northern Wdshi; rlgton. Clacial st;-iae indicate ice movement from the north and northwest (5.S.C., 194O), but such flow directions prcbably reflect a high degree of lccal topographic control.

Ice erosion has gougd tho main val ieys of the Simil kameen and

Okanayn into deep, steep-sided trenches, a113 the52 have teen partly f ii led with glacial debris and recent alluvium. The bedrock val ley5 3re xuch deeper, with the floor of the deepest parts sf Okanagan Lake lying below prespnt sea level. Glaciati~nappears t.j hzve ended about

10,(!00 years ago, fc;lIuwinc~an abrupt shift to oariwr 9r drier condi- tiorls (Fultor;, 1969). Sts~nantice remained -in the mair, valleys for sclrle time after the ripland s:..eas were expoca!, and the present valley floors display a complex series of kame terraces and kettled outwash features. In addition, local ice damming of the me1 twater formed a series of temporary lakes in which lacustrine silts and coarser deltaic deposits accumulated. Remnants of these features may be seen on the valley walls, often several hundred feet above the valley floor. Level upland areas retain a veneer of till and outwash material, but this has largely been removed from the steeper slopes, where thin soils and bedrock outcrops are the rule. The material so removed has been col 1ec ted 'in the deeper val 1eys as a1 1uvi a1 fan depos its , over1yi ng the older glacial material . Such fans form a prominent landscape feature in the Simi1 kameen Val ley, often covering the entire valley floor, from the valley wal 1 to the river floodplain. In contrast to the outwash materials, the fans tend to be poorly sorted, but become finer and more stone-free downslope. Although the bulk of the fan deposition appears to have taken place in the early post-glacial period, the surfaces of the features are probably of relatively recent age. A prominent stratum of volcanic ash, probably referrable to the Mount

Mazama eruption of about 6,600 years B. P. (~ykeet a1 . , 1965) may be traced in roadcuts through many of these fans in the Similkameen Valley, - and commonly lies five to ten feet (1.5 - 3 m) below the present surface. In many places the valley wall is formed by active scree slopes, lying below steep rock faces, and composed of coarse gravel to boulder sized material. In the Okanagan Valley a ser ies of deep lakes exist in glacially eroded pockets, or ponded behind a11 uvi a1 fan obs truc- tions . No such 1akes exist on the Simi 1kameen, and the river meanders across a broad floodplain of recent alluvium. Small lakes in the Tne climate of tb-: area is cf a mild contirentdi type, character?7ed by hot summers, and relcrt ively mild winters (Kendrew and Kerr, 1955). Climatic noma?s for s2lected stations are shown in

Figure 2.2. Precipi tatiw patte:m sho~tw yeikr7y maxima, one in r~~id- winter and the ~therin eariy summer. Tkre is a yenural tendency for prec-i 2itation to i ncrease r:or thward in :he Clkanagac Val 1 ey , and westward in the 5irni ;kameen, ~utthe mai n ccntrol on preci pi tati on is elevati $11, with the oroyi~~~hicc:ffect being most pronounced in the winter, when thp precipi tat: nn is of ~:~c?c::ic~ri yl n, znc; 1.2s: ~~tir-k:.d ;r-I the smrer i~i~et? * much of the rainfall originates fn convective storms (see Table TI. 1;.

Ternperatl.rres vary wi th elevdtion as we1 1, with wan daily lapse rates steepest 'in spring and summer. Cold dir drainage into tile valley bottcnis from far upslope resuf tc in strong diurndl pattevtis, and may account for the reduced :.,i r.ter3 lapso \rates, when co~;vectiotxl n!i xi ny -is recluced. As a re.ii!t, 9-f the cold air drainage, statioqs or; the higher valley bewhes i~ndtq haw hiaher mean summer ie~peraturesand 1or:ger frost-free seasons, and such sites are preferred locztions for sensitive tree irti-i ts.

* Van Ryswyk --ct a'i .. (1956) cxarr,ir!ed c? inlate variation along an alti tudit-:a1 trafisec'i Sfi the K.a;;;l~ops ?yea. They r,oted a strong oro- graphic trend in n~irisurnwr~,lj~t pi-esc:,t no data for the winter months. Medley

Fig. 2.2 - Climtic Normals from selected stations. T is tc:-y.~raturl:P is prccipi tation. TAl3L.E Ii. 1

Mean Wunthly Precipitation Vzluzs for Selected Statism, With Reyressi on Slopes and Correlation Ccefficients as a unction of Station E!? ti tcdc

Station Mi. Kobaor 01 ivei- Kei-ciwos Oso~~oos Kegres- Corre- Peri od 1966-71 1960-71 1960-71 1960-71 sion lation tude 6,116 ft. --kl t-i -.997 - .- -- ft.- -i,4lO- ft. 1,070 ft. --Slope Coef f .-

Janua p:f 2.458 in. 1.588 1,295 ,9567

February 1.752 0.685 O.%E .9581 March 1 .?/a 0.649 0.372 .9381

Apri l 1.950 0.82? 0.713 0.914 I.-3'jr;z L-4 ,9785.

May 1.670 0.956 0.543 0.988 .I630 .867Ci June 7,. 566 1.048 o e95 ,7541 July 0.791 0.877 0.774 .j.658 August 0.826 1.083 0.657 .3% 1 September 1.200 0.713 0.4',,3 .go39 October 1.447 0.56s 0.442 .9623

November 2.042 1.13i 9.765 .8799 December 4.996 2.005 1.735 .9839 Mean pressure patterns reflect the influence of a dominant high pressure cell over the western arctic in winter and the sub-tropical high of the summer north Pacific (Kendrew and Kerr, 1955). The area is subject to ocassional intrusions of continental arctic air in winter, producing very low temperatures even at valley bottom stations, and causing severe injury to the fruit trees. Water balance parameters, calculated according to the formula of Thornethwai te (1948), show high average water deficits, and 1i ttle or no surplus for most valley bottom stations, and most agriculture is dependent on the supply of irrigation water. Some mean water budget data -are shown in Figure 2.3.

111. Climatic History

Information on the climatic history of the area prior to the recent period of systematic instrumental observation is sketchy. The available palynological evidence indicates a relative increase in the extent of the grass1and vegetation during the mid-Hol ocene. Hansen (1955) and Alley (1976) have correlated this period with the Hypsithermal or

- Altithermal interval widely reported in both Europe and North America (Lamb, 1971; Bray, 1971). This conclusion appears quite valid, a1 though r the warmer or drier conditions which probably existed at this time are i E not detectable in the adjacent coastal region (Mathewes, 1973). The dating of this period is less certain, but both Hansen (1955) and Alley (1976) affirm that the pollen zone on which the inference of warmer climates is based straddles a stratum of volcanic tephra from the Mount Mazama eruption of 6,600 years before present. On the basis of Fig. 2.3 - Noisture Galai~ceiat.5 for th2 study cwa. P.E, is potentia.? evapotranspi ra.ticrc,A, E. is actual e!!?not;rar:piina?~ia~. The soil moisture inde?: value i.0 reprerenTs an assuncd Sie!d capacity of 14.0 cn, 'dsiues sre i,s i-'ractir>r:r, o' fie?:: capacity . palynol ogi cal evidence, A1 1ey (1976) has hypothesized several succeedi ng periods of a1 ternati ng warm and cold condi tions, but these i nferences must be regarded as tentative unti 1 further information is avail able. More recently, the area was probably affected by the 'Little Ice Age' interval of low temperatures in the seventeenth and eighteenth centuries , which caused glacial advances in the Rocky Mountains (Luckman, 1977) and which is recorded in the tree growth chronologies from Yoho National Park (Bray and Strui k, 1963) (Fig. 2.4). The available geomorphic evidence indicates that this glacial advance was generally the most extensive si nce pre-Hypsi thermal times (Luckman, 1977 and personal communi cati on) and i t may be inferred that the correspondi ng cl imatic conditions were the coldest or most prolonged during the later Holocene. The data from Yoho (Bray and Struik, 1963) indicate that the progressive amel ioration which has occurred since has been interrupted by at least two reversals, in the last decades of the nineteenth century and again after 1920. It is difficult to ascertain the magnitude of these temperature fluctuations in the field area, for the local tree ring record (Stokes et al., 1973; Schulman, 1946) is apparently sensi- ti ve to moisture avai 1abi 1i ty (Fig . 2.5), rather than temperature, and conventional tree ring analysis is relatively insensitive to fluctua- tions of more than a decade or two duration. However, the local record of tree rings does indicate that moisture availability has fluctuated markedly over recent centuries (Fig. 2.6) with significant changes at scales of up to a decade at least. Observational records of temperature and precipi tation within the field area are available from 1913 and 1921 at Penticton and

Fig. 2.5 - Penticton Tree Ritq f ndex as function of actual evapotranspiration. Ttw Ring 9ht.a from Szhulrnan, 1956.

Kererneos , respectively, iind for shorter pelniods at c;thcr sta ticns.

These data have beer? transfcrmd t3 regional water bz,l5:~:*.eest-i~nates,

usi rig the formul a of Thorwthwa! ic! !1948). \\later deficit est-imz-Les (Fig. 2.7) are relatively high through the decades of the 1S2iDZs and

19301s, low during the l!NO't;, a:-ld rise to high levels agait-i -tl;rcugh

the 1950's and 196G's. The cliniste of the awa thbs S!~OWS a degree of variation at a nuaber of different time scales. The inplitatir3i11; of

JV. ---Soils

The a1 titud-inal cl imatf r t:.end; ir the val leys of the study area givc rise to a series of foirr zow! soil groups, k;i thin a:i alti tudinal cdtma, and these art: furher divided into soil series arid phases cn the bdris of parcat mr:?t rid15 and t.eXt~ir~~Sattr-iblltes (Kelly and Spilsbury, 1949; Sprout and Yz;?;1, l96i). The sequence extends from Browrt and Dark Brown soiis ar! f3n and terrace surfaces in the valley bs.ttoins, thwugh Elack (Cilei.n:~zcmic) soi 1s with tmnsi tion to more mes5c condizio~~s3'6 h

The Brown and Dark Brown soi 1s typ.ically have surface ilorizor~s which are brown, dark brown or grey-brow in cu!ou~%,weakly grsnular in texture, and neutral to sl igi-itiy a.l kzi ine in resct,lon, overlyi r~g s tructurel ess or weakly col armnai- Ocrizons , w,l t!i some l iPIC accumul a- ti on at depth. Textures vary wi th -tkii? par.e:~C materi a1 , thse devel c?ed on fan surfaces beinc; silty to fine sandy loans, ar:d tkost- :,!I the oui- wash terraces being coarser, often ranging t~ ~r!odcraS;~lycoarse gravel.

Most are weli drained. A1 thovg!~large aw,s of these so5 is, in the vici ni ty of Keremeos and Caws ton .i n the Sii:ii i :c;ln:eer! Val ley, and S n much of the lower Okanagan Valley, are in use for irrfg~.tedagriculture, large areas remain as unimproved rangeland, ard ccrnnior~lysupport stands of sagebrush. These soi 1s are be1 i eved to have dewl oped under 'nearly pure stands of bunchgrass ~kqro~ron--..-. .- . -- - w~?tiinll .- apd to hzvc been recently invaded by A.- tridentata (Sprcut and Kelly, 1361). The Hack soi 'is of the area i-iav? :t!rfa(:;a hob-izons which are black, very friable, powdery when dry, contain abundant grass roots, and have a slightly nmre acidic rcaction than the Dark Brawn types.

B horizons are comn!only bli7ck: to dark brown -in colcur 2nd coii.irr!nar in structure, grading to ye1 low brown, and structurxiess wf th same l ime acci~mulationat depth. A1 tnocyh thew soi 1s are relatively common west of Hedley and in the nor therr; p2rt of the Okanagan Val ley, they were encountered at only tw~places within the field area, at 3,000 feet (914 rn) on a west-facing hillside to the north of Cawston, and on a steep north-facing hf llsid? mar Twill Lake. Eoth tireas were located at the edge of Pseud~iS~3a- forest, and appeared ta be quit2 limited in extent, -Artenisis------iridentata -- is found rather izf re~~usctly on such sails, but it will be shown ths t the Cawston sf te appears to have been recently invaded by the species. V. Natural Vegetation

The present natural vegetation of the study area may be

characterized as an altitudinal sequence similar to that described

for the soils, and often showing close correlation with the existing

soil pattern.

The first modern descriptive work on the vegetation of south-

central British Columbia was done by Spilsbury and Tisdale (1944) and by Tisdale (1947). More detailed discussions of the vegetation in the field area have recently been pub1 ished by McLean (1970) and Brayshaw

(1970).

The primary physiognomic division within the vegetation of this area is between grassland and forest, the grassland being confined to

the Brown, Dark Brown and Black soils, and the forest occupying the more heavily podsolized profiles at higher elevations. Within the grassland, Spi lsbury and Tisdale (1944) distinguished three zones--a lower, middle and upper grassland corresponding roughly to the Brown,

Dark Brown and Black soils respectively, and this division was followed by Tisdale in the paper of 1947. The lower grassland type is dominated by Agropyron spicatum, Poa secunda, and Artemisia tridentata, with - lesser amounts of Artemisia frigida, Chrysothamnus nauseosus, and

Antennaria dimorpha .* Tisdale (1947) suggests that under the influence of heavy grazi ng, Agropyron decl ines , and Poa , Antennaria, and Artemisia tridentata increase, to form an Artemisia tridentata - Pea

* Nomenclature fol lows Hi tchcock et a1 . (19%). A complete 1ist of authorities and common names will be found in Appendix 11. 27 secunda disclimax. He suggested that some reversal of this trend may take place under conditions of light grazing and above average rainfall.

Minor communi ties incl ude a Stipa comata - Sporobol us cryptandrus association, and a Purshia tridentata - Stipa comata association, both on coarse textured soils. Bromus tectorum is noted as a common invader in disturbed situations.

Within the Simi 1kameen Val 1ey, McLean (1970) has described two

Artemisia tridentata communities which appear to correspond to the lower grassland; the zonal type being an Artemisia tridentata - Agropyron spicatum community, with an Artemisia tridentata - Poa secunda type being confined to shallow and coarse textured soils. Again,

Agropyron is noted as a 'decreaser', and Artemisia tridentata, Poa,

Sporobolus and Bromus as 'increasers' with heavy grazing.

Several species apparently represent recent invaders of this setting. Bromus tectorum is an annual grass of apparently European origin, which has invaded this area from the south, and is a common colonizer of disturbed areas (Young et a1 . , 1972). Sal sol a kal i appears to have invaded the area after 1902 and was noted as a problem weed by

1913 (B. C. Department of Agriculture Reports, 1902, 1913). A1 though - relatively common, it does not appear to represent a serious weed threat at the present time. Sisymbrium a1 tissimum, also of European origin

(Hitchcock et al., 1967) is common throughout the area, and may form nearly pure stands on recently disturbed sites. Centaurea diffusa is apparently a very recent invader, and is notably absent from McLeanls description, a1 though it was widespread in disturbed locations in the lower part of the valley, below Hedley, and in the White Lake area in

1973 and 1974. 28

Agropyron spi catum, or bunchgrass, is usual ly designated the climax dominant in this lower grassland zone. It is a deep rooted,

perennial grass, usually forming distinct clumps or bunches, but becoming rhizomatous in more mesic situations (Hi tchcock et a1 . , 1969).

As a bunchgrass, it frequently leaves much of the soil surface bare

(Tisdale et al., 1965), but the proportion of bare soil diminishes with transition to more mesic situations (Stoddart, 1941). Daubenmire (1970) noted that it does not stand up we1 1 under heavy grazing, and suggested that its recent evolutionary history may not have included any signifi- cant grazing pressure.

The middle grassland of Tisdale (1947) is roughly coincident with the Dark Brown soils, and in general tends to be developed under more mesic conditions than the lower grassland. Dominants include

Agropyron spicatum and Poa secunda, with Koeleria cristata, Artemisia frigida and Balsamorhiza sagittata as prominent components. Tisdale notes that Artemisia tridentata is confined to the lower portions of the zone.

This vegetation type appears to be comparable to the Pinus ponderosa zone of McLean (1970) and Brayshaw (1970). A1 though McLean does not include drtemisia tridentata within this zone, Brayshaw defines a Pinus ponderosa - Agropyron spicatum association similar to one of the same name described by McLean, but with Artemisia tridentata as a prominent component. He notes that Artemi sia tridentata is more frequent on heavier textured soils, and at low elevations, and tends to increase with overgrazing. A Pinus ponderosa - Artemisia tridentata subassociation is defined as a grazing disclimax. These different views of the middle grassland may ref1ect differing interpretations of the probable climax condition, or slight differences in the study area. Communi ties contai ning Pi nus ponderosa interdigitate in a complex fashion with grassland communities in which

Artemisia tridentata may be present as a normal constituent, or as a recent invader. It is perhaps best to regard this zone as an ecotone between the grassland and Pseudotsuga forest, in which -A. tridentata decreases, and Pinus ponderosa, Balsamorhiza, and Festuca idahoensis increase with transition to higher or more mesic condi tions . Brayshaw considers that the lower limit of Pinus ponderosa is set by the combined effects of moisture shortage, increasing frequency of ground fires, and seedling mortality due to high soil temperatures in the absence of shade.

The role of fire as an ecological factor in this area, and the factors which determine the upper limit of sagebrush will be discussed elsewhere.

Tisdale (1947) defined an upper grassland zone, dominated by an

Agropyron spicatum - Festuca idahoensis association, lacking Artemisia tridentata, and approximately coincident with areas of Black soils.

McLean (1970) has noted the existence on these soils of two communi ties of interest. One is an Artemisia tridentata - Festuca idahoensis habitat type, which occurs locally within the study area, but achieves its best development in the area south of Princeton, where McLean suggests that it may owe its origin to the presence of bentoni tic parent materials.

The second is an Artemisia tripartita - Agropyron spicatum habitat type, on Black soils, at elevations of about 1,000 m. I have observed similar stands west of Penticton and on the east side of the

Okanagan Valley. Artemisia tripartita may also be found as a co-dominant with -A. tridentata on Brown and Dark Brown soils under relatively xeric conditions, near White Lake, and in the lower Simil kameen Valley, and in these situations the plants are commonly somewhat larger than at higher elevations.

In general, however, these chernozemic soils were observed to support grassland, or a lush grass and mixed shrub community. McLean designates a Festuca idahoensis - Eriogonum heracleoides habitat type as being most characteristic of these soils, and suggests that it represents an edaphic climax on parent materials with low moisture hol ding capaci ty . Two well-defined forest zones lie above that characterized by the presence of Pinus ponderosa. The lower one is dominated by

Pseudotsuga menziesii, var glauca, and the upper one by Abies lasiocarpa. McLean indicates that the boundary between the two types lies commonly at about 1,350 meters in elevation. Subdominants in the

Pseudotsuga zone include Pinus ponderosa at lower elevations, and Picea engelmannii . Sera1 species incl ude Pinus ponderosa (Brayshaw, 1970),

Pinus contorta, and, to the east of the Okanagan trench, --Larix occi- dentalis. The Abies zone includes Tsuga mertensiana, Pinus albicaulis, - and Larix lyalii as minor elements. Pinus contorta and Picea engelmanni are the dominant sera1 species. Within the Abies zone, McLean describes isolated communities of Artemisia tridentata ssp. vaseyana and

Cal amagrostis rubescens. The taxonomy of Artemisia tridentata wi11 be discussed in Chapter 111.

Independent of these zonal sequences are communities developed along stream and lake margins. The most prominent of these are the floodpl ain comuni ties of the 1ower Simi1 kameen and Okanagan Val 1eys .

Populus balsamifera and -P. tremuloides are perhaps the most common

tree species, but A1 nus tenuifol ia, Betul a occidental is, --Sal ix spp. and Cornus stolonifera are frequent elements. Alnus and Betula are

also common along smaller stream and lake margins. Pinus ponderosa

and Pseudotsuga form conspicuous stands on the insides of bends on the

Similkameen River, and may represent fire islands, or sera1 stages in

the f 1oodpl ain succession.

In summary, the Artemisia tridentata population in this area

is concentrated at low elevations in the major valleys, in areas which

typically have good drainage and high annual water deficits. Within

these areas it tends to form closed stands, and appears to be the

dominant species present. On higher or more mesic sites, the species -- is less common, occurring as scattered individuals, or as isolated

stands of density comparable to those at lower elevations. However,

it is seldom clear whether these isolated stands owe their origin to

particular edaphic factors or to local historical causes, such as

disturbance. Dominance on these more mesic sites is frequently shared

with other shrub species such as Chrysothamnus nauseosus,- Artemisia

frigida and Artemisia tripartita, and with a variety of grasses and

forbs. Only rarely, however, are these other shrub species found at

densities which suggest direct competitive exclusion of Artemisia

tridentata. The reasons for the absence of Artemisia tridentata on

higher or more mesic sites are unknown, but the spatial patterning of

community types suggests that it is 1inked to climatic conditions, and

perhaps to competition with the understory species. In spite of the VI. -Settlemnt -- and La~dUse- -. .-

The area has a long hisior:! of 1rit;iai; ccciijiance, datirig to at

least several thousand jcars (\;;I mth, i9it 1. Tk Indian ecr~nwiap~ears to have been of the hunting ar~duat.i~er.inq type, but, rathrr 7 i ttle is

knawn of twjr iinpact 1!?0n the landscape?. F.urc)?ecti set tlet;tr~f, WS limited to fur trade activity until the disccver!i of gold in 1853. Thc Okanagan Valley was part of the fur hr.l:gade rcute from Fort Vancouver,

a1 though it appcars to hay? beer1 re'1at-i ve I;/ l I tt.1 e used. !t .i c, yssible, however, that sonie local overgrazing by pack ii~imalsprwhtes t:le intro-

duction sf cattle and sheep to the area

Placer mining was nevsr very important, a1 though ttlc area was

intensi vel y prospected, and rmny small s tr-ikes weu.2 made. 1 he deiiis~d

created by the Cariboo mines, howsver, stimulated the gr~wthof a ranching industry. Cattle were introduced to the area in 1860 (Orrxsby,

1931) and the industry grew stcadjly unti 1 the end of the century,

although i~amperedby the lack of available markets 2nd poor transport-

-ation facilities. Orinsby (1.931) mtes that there were 2,096 head of

cattle in the Keremeos area ir~1893 and some 2O,i)O? in the Okanagaw

Sim-il kameen area as 2 who!n. Nuri;bei-5 ;Ire abc?~;rt-the same today (D.B.S.

Census of Canada, IYiI).

IY'ier (1953) has discusr;ed r.i:c ~i-siling indss try cf British Colutnbia in some detai 1 . Traditional patterns invo'l ved a sczsonal transhmance in which the cattle were win-tered in the valleys, often with little stipplementary feed, and were ri!ovec! to h.iglier, morz mesic ranges for the summer. The lower. sfigebrush ranger thus cam under heavy pressure .it\ the early spring and winter ~~anths.This pattern is

particularly tlest.w~c.tive"L the native CjiaaSSESt which must. make all of their growth, and reproduction, prior to the exhaus tion of soi 1.moisture reserves in eariy summer. This pattern has sndergone some change recently, as improved irrigation techniques have a1 lowed ranchers to grow and cure iray for winter use. It is not clear, however-, that this

has resul ted in any reduction in grazing pressure. Nost winter range in the area appears to be fui ly utilized at present.

Cattle nuinbers appear to have tiecliried son~ewhatafter the decad~ of the 1890's due to range depletion and incrased settlement of the val 1ey bottmns (O~illsby, 1931.). Certzi nly cattle nun:bers i n the province as a whole declined in the period 1891 to 1906 (Urquhart and Buckley, 1965). Census data for the southern Okanagan - Sfmilkameen shgrjest that cattle nuinbcrs on occupied farri~i and have been re1 ative'iy constant at 4.5 to 6.0 beasts per hundred acres since 1931, with a slight peak

(9.3) rec~rdedatthe time ,sf' the 1561 cerlsus, and a decline to 4.5 -in

1971. The 1893 dat.a yield estiri~atesof 6.7 for the er~ti'reOkanagan region, and 14.7 for the Kereseos area, while thz cnrsus of 1881 implies an ,incredible 32.5 beasts per hundred occupied aci-2s in the entire Yale district. The 1881 figures unrlcub-i;edly underesti'iiiate 'tho 1 ange 1 and actual ly in use, and this. may be true of the 1893 dzta as we'l I. The suggestion, as early as 1870, that a stocking liniit of ten. beasts per hundred acres be enforced rjn 1 dnds held u,,der yra;i nq 1edse.; (15 i kkel sen,

1950) suggests that som areas were stocked in excxss of this figure, and that overgrazi rrg , at l ecs l; l0c3l ly, was sl rtihdy apparent.

After 1830 many ldxk were trans r'erred to agri c~ltura: use, although some were subsequently abandoned (Lacey, 1951) and returned to rangeland. Ormsby (1931) has treated th2 ecnnr,!l~ichistcry of the fr~tit industry, which occupies much of this land, and which, af terb 1300, rapidly displaced wheat growi ng as the pri nci pzl agricul tural activity.

Fruit growing commenced in the area about 1890, and expanded rapidly in the Okanagan and around Keremeos in the SSrnilkarneen Valleys. At present, there are some 14,553 acres devoted to irrigated tree fruits in the area (D.B.S. Cenqus of Canada, 1971). An additional 8,188 acres are irrigated for forage production. Most of this activity is located on the surfaces of terraces and a1 luvial fans in the main val ieys, but considerable areas of these features, and virtually all of the higher and steeper lands, remain as unimproved pasture and woodland. CHAPTER I11

PREVIOUS RESEARCH ON ARTEMISIA TRIDENTATA

The purpose of this chapter is to review the existing literature on the taxonomy, ecology, dynamics and population hi story of Artemisia tridentata. Because the species has been identified as a weedy invader of natural grasslands, and because it has been repeatedly shown to depress forage yields on i nfes ted ranges (Robertson, 1947; Harni ss and Murray, 1973; Cook and Lewis, 1963; Frishknecht, 1963), research has often been undertaken in a search for management practices which will effectively control or eradicate the population, and the existing liter- ature is extensive. The material has been grouped under seven topics: taxonomy, 1i fe cycle and phenol ogy , seed1 i ng ecology , environmental con- trols, a1 lelopathy, population dynamics, and paleobotanical studies.

I. Taxonomy

A. Artemisia tridentata - The taxonomy of Artemisia tridentata is complex and poorly understood, despite a considerable amount of recent work. Two named subspecies are generally recognized (Hitchcock et al., 1955) and several more have been suggested. Artemisia tridentata ssp. tridentata is the name generally assigned to the lowland form of the species, while Artemisia tridentata ssp. vaseyana tends to be restricted to higher and more mesic situations (Beetle, 1960; Marchand, 1964;

Winward, 1970). Marchand et a1 . (1966) have shown that Artemisia tridentata -ssp. vaseyana in British Columbia is phenologically and

ecologically distinct, and with Taylor et al. (1964) state that in

British Columbia it is diploid (2N equals 18) while Artemisia tridentata

ssp. tridentata is tetrapl oid (2N equals 36). Recently, however, Kel sey

et al. (1975) have documented both ploidy levels in populatians of

Artemisia tridentata ssp. vaseyana in Montana, and have suggested that

these earl ier resul ts be re-exami ned.

Winward (1970) has recognized five subspecific groups in Idaho.

Three of these are subdjvisions of an Artemisia tridentata ssp. vaseyana

complex, while the other two, Artemisia tridentata ssp. tridentata, and

Artemisia tridentata ssp. wyomingensis, are found at lower elevations.

Winward's map (p. 33) suggests that these forms may be segregated on the

basis of elevation as we1 l , with Artemisia tridentata ssp. tridentata

being found in the lowest parts of the valley bottoms, and being succeeded

by Artemisia tridentata ssp. wyomingensis and finally by ArtemisTa triden-

tata ssp. vaseyana with transition to higher elevations. These distribu-

tions appear to be adjacent and continuous. In British Columhia, however,

Artemisia tridentata ssp vaseyana is segregated from Artemisia tridentata

ssp. tridentata by intervening forest, and mixed populations are rare

(Marchand et a1 ., 1966). Kelsey et al. (1975) have recognized three distinct races of Artemisia tridentata ssp. vaseyana in Montana, and have hypothesized that extensive hybridization among them is 1imi ted by

some unknown post-zygotic mechanism.

Beetle (1960) has described what may be a further varietal form, Artemisia tridentata ssp. tridentata f. parishii, which is reported to occur from British Columbia to Nevada. It appears to intergrade freely with Artemisia tridentata ssp. tridentata wherever found. Marchand (1964) assigns the low elevation subspecies in British Columbia to Artemisia tridentata ssp. tridentata, but may be following Beetle (l96O), who did not recognize Artemisia tridentata ssp. wyomingensis. No attempt has been made in this study to distinguish subspecies, and the data may apply to Artemisia tridentata ssp. tridentata or Artemisia tridentata ssp. wyomi ngensis , or both. As the study was restricted to low elevation sites, Artemisia tridentata ssp. vaseyana, which is relatively distinctive morphologically, was not encountered. The present distribution of Artemisia tridentata in southern British Columbia is shown in Figure 3.1.

B. Other Species of Artemisia

Several other species of Artemisia also occur in the study area, but only two, Artemisia triparti ta and Artemisia frigida are suffici - ently common to contribute significant amounts of pollen to the regional pollen rain. Artemisia triparti ta tends to occupy somewhat higher and moister situations- than does Artemisia tridentata, and may hybridize with it (Marchand, 1964; Tisdale et a1 . , 1965). -A. frigida extends south to California, east to Manitoba and Kansas, and north to Alaska and Eurasia. The problem of pollen taxonomy among these species is treated in Chapter VI. Other species reported to occur in the area include Artemisia cana, Artemisia dracunculus, Artemisia norvegica, Artemisia trifurcata, Artemisia ludoviciana and Artemisia campestris. Of these, only the latter two wereobserved in the course of the field work. Figure 3.1. Distribution of Artemisia tridentata ssp. tridenta ta in southern British Columbia. 11. --Life -_-_XI.- Cvcle and Phenolcqy___->_

Artemi s!'a 4;r-I 6eni:ata- fl ewers i r: 1att Septembel- and Cci-o!)er i n

British Columbia, and sets sew! in !icveliii;cr. Dzuhennire (1975) has

remarked that in blashingtcn tile plant .f'lowers '1;ef~re the onset of the winter rainy season' . The seed is an achene, 1 - 3 m. in length, with longitudinal ridges or ribs. Goodwin (j.956) gives ail estimate of

335,000 seeds from one plant, but seed production is appa;wtly variable, i

and may bc! qu-ite low in som~locatior~s :3r in sere years (see Fig. 4.13). I I The variation may be related to soil depth or water avaglzhility

(Robertson ind Pea?-se, 1945; hubermire, 1975). I

I Goodwin (1956) fcilx!. that n:ost. seed ti-aveicd iiss th2n 33 rn.

from the parent pl ar:t , but ily~othesized that :,orne 1o,-i$ distance transport

in cattle !.lair hlay rwc-~jy. tdc.l;g;?! e:.' (.19;t: j 1-;as pt-esnntiid s3w evici?!rlce of persistence oT viable secd in the soil for several years. Limitations

I on reproduction due to seed .a,vaflability may thus b? partly redticed by 1 the presence of swd st~rec!fr~iii parids of high productian or nearby seed sources.

Plants flower zt three t? four years of age (Goodwin, 1.956).

Flower buds form ir: June 2r.d deve?op slolfi~'lythrot;rj!:ci~i: the summer when other t~egctittivegrociti: has ;past.? (Dah..tr:;nire, l9?jj, ikxin~~:mages of over 200 years hsve been v.epur.ted (i-'eryusu11, 1!?64j, Sut this ?pp?ars to be exceptional, aid rilants over 100 years of age are re1a:tivelj rare.

L I 1. Seedl i no Es9l oqy _ _ _ d..--

In a species such as .i?rtr?.::isjz --.-.t.;ti:ienta -- ta :.:hi cir r?pro,A.ices entf re'ly fro? see?:, SH<:C:S:~~~:]9rrii:i mi3 or! a~,:~~?::dl -i!n(~ ES t&(L;'!i~f!nic?iil; is a necessary prerequi si f,e for poplrlati on expansi or) or. n;ai nteimncs.

This is a particularly hazardous stage in the 'iife cycle of mny swcies,

for the seedling has low assimilate reserves ar-!d a poorly establisl~ec!

root system, and may msily SUCCW~? tr3 perjods of i~clerlientxeather,, or

to competi tiori f'run: me~:be!-s of the established com~nunjty. F3r these

reasons, the seedlicy has bezn s.ing1cd cut as a disrinct 1 Sfc stage, even though the eract poirit of transition frog1 seediinq to adult may he difficult to identify.

A. Germi mtion-

Seed germi txti on OCCUV'S I R early spr i ng, ai1.l ma:{ be cnha~cedby freeze- thaw condi ti ons (Daubermi re, 1975). G~rmiriati on is enhanced by stratification and I i~iit, and scq;r-i decjree 2.f fi:!frrcerJ dorrwncy has beerr reported (Weldon et a:. , 1959; !/l:i)oi~~u~~h2nd t:arni5s, 197?),

Bare nrinera? soil seedkds nisy tend to enl.iilr\ce gzrmination or subsequent seed1 i ng survival . Jobi?son (1958) hypothesized that poor gemination was related to t!~preserlce of grc;ss 1i tter. Stoddart (1947.) and Johnson and Payw (1968) sug~cstedthiit fo'tiiler grassland may have been converted to sagebrush by pioughi nc and s!:bsequer~t abandonment. Similarly, Sears (1946) arid Emth (1942) r!ave ~irgires'the role of rodent disturbance, and have I f nked -,4r-- - i.w:isia ------k~i --- dentat3 --. .- -. .- -- invasions to predator control programs. Bleak si.jd Mi :leu. (1955 j dcjlcir~istrstnd that mechanical eradication of the shrub, psrticular~lywhen ccnducted in late sumner or fa1 1, frequently leads to at!knc!znt regencr~,ii~:.!, ard argued that the clsariny activity serves to 'scatter and p!;\i~t' ?.he seeds. 6. -.-Growth - and Survival-- ~eediing growth and survi vsl have hecri ral~tedto teqwnture

and moisture supply. Johnson (1358) aml Johnson and Payne (1968) have

reported high mortality in first year seed;ing populatiotis, and have

hypothesized that summer drought may be respr?iisibl e. Dacri:cnmi re (1975)

has rernarked that -Artemisia -. - -tridentata. ------. - seedlings ht?.~arily a liniited

drought tolerance. Several workt:rs haw 6.ttr-ibuted pwr sagebrush

establ kshlrient i r! heavy sod to rnoistut-e conpcti tion wi th the est~blished

grasses (Booth, 1948; Blaisdell , 19119; Johtlsot!, 1958; Pechanec and Stewart, 1.344.).

Harniss and McDonough [i975) h~veexat;,l r,ed swdl irq respcnse tc

different temperatu:-e regimes. It'oi*king wit!; pi-ol/enances from Idaho

under cor;ditinns 't ti tended t;c s'm'late avev.i:!je, d!lo\i~average, and be1 9:::. average spring temperature regin;es they [ourid t,i;,lt gxwtli rates were five to seven tiriles greater ur~rfci-abcve ?vcr;lcje conditions than urjder below average conditions. Usspi tc I-kcse dif iciqencss they concluded, on

the basis of lou seebl-i nq mortal? ty, tha'l I:. . . year to year temperature differences are not cri ti :a1 in -the detcrwi m-Li on of succc!ssful re- establ i shment,. " This c~rlc!us:'!jn rlldy h2 ~ucs-L.~~)i:~d, for it WOU~d seem

that high early growth rates may be crit.irz? in the rievel~pmentof a root systeiii ~dequateto cepe witi? the mrri stuire shi;:.tagc? wh; cfi cornxionly develops later in tt~year.

Marchand --et -- - -.a1 - . (3.966) worl:cd ~i th yctlnq plants of Artenii sia - kirlter -t;r-id~nt?.'iz - --. -. -.- - i i; ~;~pe!-jr~wntalgci%-d~r1s in souttlerrl Eri?.ish Cn! umbia . cr 2ar.i~spr.ini; injtsr-y 1x1 tl.1~p'lar!ts was cbuervzc!, and hi2h nrnrta'litj, in

c;c.u!;i;c?-r; prC-vena,?ces ~J;;-s~ttr-.; kut-c.4 t~isevere w? ntcr w;; tiit?.. Grewth 4 2

rates of up to 61 ca. 51.1 t~oyears were ~bserveiiin these experimental plar~tingsbut field obser~3t-icnssuggest that such r-ates are exceptional, and may be a result of rethccd conpeti tion in the ~ard~rienvi roninnnt.

Plants under 15 c~.kall at ti::-eu yezrs are not ur!coirimon under field conditions. Daubemire (1975) reports qrw~th'aim of up to 5 cm. in the first year.

JV. Env-i ronn:ental Controls of Remi tv acd Ranae _.II__.------i-- --.-

Many studies have attempted .to re1 ate the density or distri bucion of mature -Ar- tanisid-- -- -. .tridentata- --. - - plants to vcvious fzcrors in the enuiron- mental complex. A1 though these s-tudies deal wi th nature plants, it is often unclear to what extent the observed patterns reflect processes which primarily affect tk,e adu'll. nlant, an@ .ihcse vh'ich p,.';~i~zrily affect the seedling. This section includes studies wh.ich deal sprci fically wi th the adult pcpulation, or in which the seed1 i q-adul t distinction has not bwn made.

A. --.--clirxrate l-[le (;o:~r.c1ation b?tweei, ti,? I c\catic,c af sagebrush stands and the cl imati c envi r.::ric;~nt has bee,^ I'CCOCJ~.: zed fgr r!xir?\/ y~ar~. Weaver and Clements (13313) and Stoddart (1941) have rmarked tha.1; (:he areas in which they consider -Artmisia -.- - .- .t;-i- den tata--- to br. I.hc climax domi; nant are characterized by artt?ual precipf tat. ion OF betienil 13 .LO 26 cw. with a strong tendency fo:.. 6 \vi nt~r~fii:;;.imu!~l. They r!:jte;f thrt une'?? the i nf1 uence of overgrazing the rs!xje of f:h:.: ;jfc:.it h.ls ~?xt~r;decltc? arcas with up to

50 cn;. of annuai greci pi ts tior!. While it 5s evident that sagebrush is limi tcd to areas wi t.h high

annual moisture def-icits, the 1 imi ting mecha~?isrnhas received !i ttle attention. Harniss and Murray (1973) noted that both above a.nd beiow average rainfall have been used to account for sagebrush invasions. This

may reflect observations aade at both the xeric and mesic limits of the range. Any mechani s!n which is proposed mast xcount both for the restric-

tion of the populaticri tc semi-arid areas, arid the apparci~tdrought sensitivity of the seedling.

Mature sagebrush have been stmwri to have a deep and extensive

root system, often w.i .;h one zone cf shal SOY root cc~!lcei>-trat.ion,and another zone at depth (Weaver and Clemznts, 1938; Robertsot?, 1943; Cook

and Lewis, 1963; Daubenmire, 19751. Such a pattern may tend to reduce

dependenc~on water withjn the grass root.ing 7one for mature plants.

The importance of deep wter reserves has been shown ty studies of stez wood i ncrerne~t,which have beet-I posi ti ve! y coi-re?atcd w-i ti; the aniount of winter rdin prim to the grnwi nz sedson (Feuguson, 1-964 1 and to soi 1 moisture 1eve1 s i n I ate spri ny (Daubenmi r?, 1975). Ferguson (1554) has

hypothesized thar, severe druuybi; rrqt cdlrse the death of pilrt.s cf the

stem cambi:m resulting in steci 7 2bc t'or!:i:tti~r!. Eli 'son ad ljoolfol k

(1937) attributed nish rnortai j ty in -ArtwFs-ii? .-. - .- .. -- .- -t:rjdeni.a.ta - -- -. -- - stat~ds4 n

Montana to the e.ffects of ifrcugkt.

B. Soils 1959), but there ftVJ?S f~~iixiStat -Artemi;ia-- 'Lriciental3------:~rr:~~-iedor1 the

05 ~f an; of greatest variety SO^ l types the specic: ci' -P,rie!ol:sia ------studied. In idzsh: ,;gt:li, i:w,:ever, Daiiixrirni re (1340) h.i~ cLservcd that sagebrush s tands are i zrgcly coi~i~;?cd to ~.;;nd;l s treati; terraces, and are general iy abren t frw the f-inek- "Lxtur~.-ls~; i5, of the !i?iards.

ksie and Hugie (1962) investjgatcb ii~c: strucwre dnQ produc- tivity of ur~dfstwh~tisagelrush stands over m~chof the Inr thern part of the species' range. The resulting data were pdrtitioned by grezt soil group. It was fmnd that dr-ier sites (Sierozeins , Lithosol;, Saiorie tz) tend to support stards with t,bc cjreaeest mean I; izx 39e, ht .i i; is not clear to what extent these results imply recmc i~milionof nore roes-ic el: sites, or different clean life expectancies OF these soils. m

Eransotl -el - -- -171. - . j.1.970) d6-d Rranso:i end Cham (1975) Ivve dernon- strated that _A_rt>mi~Siitridcnt~t-g is able to utilix sol 1 noisture down to moisture tensions cf 50 to 60 bars. A close i*elatlai~stlip betwen internal plant moisture tcns-im and the minimum xois twe tensf on within the soi 1 prof i 1e was ciemonstrated. The average depth of maximum soi 1 moisture depletion was four;d :o 3.3 50 CK. Whi'le these cbser\mtiuns, coupled with rai nfal i ard sot? moist~re retention chariicteristics , may servo to explain the xeric 1-im;t~aC ttx ~.pr:ies nye, thej: appear to be of less va:uc -in explaining the ~esic::ringe I-irlrit, !d?tlr~such extreme moisture tensl orls are pvzsumbiy less frequent.

Charley and gest (1975) erami: red soi 1 chmi cr;l pstter'ns associ- C. --Grazig and Cc9eti tion-- Effects The topics of grazing and competiti~nare linked here because the mechanisn! by wthich grazirig my promote an increase jn sasnbrush abundance, while obscure, is presumed to relate to the reduction of competition from native grasses which graziy effects. ik~1.1of the data on this topic come frcm studies involving coctrolled srazing regimes in sagebrush stands, or from studies cf reinvasl'x -;f sagebrush fol lowir~gartificial clearance. A third grwp c.f c+cdies has cornpared sagebrush abundance on apparently undisturbsd areas vii th the abundance on nearby heavily grazed sites. The extlns-ive :

The first study of tk1e ;I-Tfccts of iirazi r!ti on ----krteni'si a trider~tata was that of Pickford (1932) Sr! ;ii;ir:l; p:-esnriled relict areas i r; cemeteries and fence corners kcere compared with aearb:! g:.az:.d areas. It was con- cl uded that sagebrush dens$ties i ncrcase In response to heavy grazing . Similarly, Cottam and Evans (1945) and Fiirll and Hull (PW4) examined ext.ensive areas of 'undisturlxi;' $/eg3_3t43ti:)n in L'tah ar;d Idaho, and con- cluded that the low sage densities c~b;::u..~~ed were rcldtc-d to reduced grazing pressure.

Cciopcr (1953) reached c-iri.,iI ai- CO~?C;1is.i OPS on the basis of con- trol led cjrari ng experiwr:ts ovev. ?.:? t?igh-L-yea7 pwiod irl >.!yomifig. We considered that sagebrush was part nf a 'disc1 imzx' vegettztion type in this area, and that ". . . ur;sler7 f~:..~;::;'ilb"ik?i.;.f.!;\thrtu. and grazing eondi- . . tions, cliniax grasses; can ddisp'!;icrt r;;~ saycbr:lsh on "chis site within a d~~~deor *I ~SS." Others have studied sma: 1 areas from ~!$fch ccttle were excfudt2d entirely. Kobertsl::n (i971) reported ail a thi r?y-year exclosure experi- ment in Nevada. Pa'lat3blc gr;s.;;.s i ~cr.r:ast:r! ~onside:~ab!yover the period, bvt production was 'less i;biin ttxt fuiic:d on warby cleared and reseeded areas. Sagebrush decreased < rl height: !wi. may have increased in dens-i'iy duri tlg the experiment. Sii:;i la r res!il ts vier? ~btair;ed by McLean and Tisclale (i.972) from exciosures estab'l.ish;d in the Kmloops area in 1936. At the one sit;! at which -Arterriis.iz ------.- --Irideritaia -- -- ws;s present, sirni lar det-rsities kere fmmd outside and inside the exclosure, a1 th~ugh the outside area was heavily grazed. Cersitics were said to have remained constafit for ten years. During the same period, F\rten;isia frigida densities were found to have increased inside the exclosure, and decl i ned outside, i nrli cati ng scirac decri2iise un&r grazi ng pressure for this species.

Johnson (1969) studied the rei nvasi on of --ArtemSsia .- ---tridentata o~ areas within which the pcpulaticn had been removed by chemical spraying. Densities on grazed areas showed a detectable increase within five years of chemical suppressiori, ard had exceeded densities cn adjacent unsprayed controi areas w.i thz n fourtecii years. On r?ngrazed plots, the population returned to contr~ldens< .ti 2: in sevrrdxcn years.

Johnson and Payne (1968) vepcirtcrl zt; rcir.Gz;icn after mechan-ical and chemical suppression, and en?phasiz:d the importance of seed sources.

Sneva (1972) documented a returr~to ?re-suppression clerlsi ties in about seventeen years, under reduced grairl: ny conditions in eastern Oregon.

Daubenmi re (1970, 1975) has repoi-led cases i n which rei nvasion after fire began ir! one to three years. The most corliplete study is that. reported by Harniss and Murray (1973) who f~lic;v~ecifor. thirty ymr-s the reinvas-ion of an area in Idaho from which Artcnisia- tridcntzta had been removed by fire. The ini tia? succession in the deczde aft,~?b~~rning involved perennial grasses and the shrub Chrvsothan~nus.:!?~rscosus, but

this stage wds apparmtly sera1 to -Artemisia-- -- tridentate,---- -. xiidse reit?vdsion was nearly complete at the end of thf rty years. It was conc;luijec! ttiat "Vegetation tre~lds. . . show the overwhelmingly dorninant role cf big sagebrush" iri this hahi tat.

There are sonz evident confl i cts -in "ii s rnateri a? , betwen

those ~33ilit~rpret the ddta ~s evidence that Artemisiz-a-w tridentata is a normal, or at least established and viable clcnicnt of the commuriities studied, and thewho consider that it would soon disappear, or be reduced to Icw detsities ;I, the dbsenc? ~f yrszing. Part of this diffrr- ence of opf nion may arise from differences in the study sites chosen, but both views dre relatively widespread geographically, and are not obviously related to the clirndx and disciimax regions of Weaver and

Clements (1938). Many of these studies may suffer frcm the difficulties of extrapelating trends frail1 reiat?vlcIy short-term observations to long- term conclusions. G!i th i. lojry-1 ivcd sp~ciessuch dr, --Artemisia ------tuidentala, ----- even thirty years obscrv3+ions may be i~2dquateLC detect real popula- tion trends, for if recrui twnt evetits a!-e rc!latI vely rere, a decline in popalation due to mrtii1.i ty wi thcut rep?ace!i~er,tmay be rr~istakenf3r decadence. Observations of the tine neccsssry for rei nvasion show re~arkcbleconsistency, gewral iy about fifte~nto twenty years, but most of these data arc de1.i v?ci fron: )-elat.< vel y :;:iis'i 1 cl earat~ces, with nearby seed sources. Val:.lcs far. rmrc ex ter~sS*~:c!~1ear;inces may be Iarser. 48

The data obtai~lec!frl.ii1: studies of 'undist-.:.irbedl or 'rcl ict' areas must be treated with caution, fcr the zvidcnw sf past disturbance may be very difficult to d~tectin a gras>la::.: r?n:;i?.c;7,wnt, and there is li ttle agreement about what constitutes 'di s t?:;i\ance1 . An exsmpl e of this problem is seen in a recent papet by Rickard (1975). The study area is described as being i ti ' pris ti re' con:!;: tion, but the i nf 1uence of past overgrazing is inferred from the presence of chcat grass

(Brcimus-- - -tectorum) - -. - - and t!le presence of fire blackend sttrinps of

Artemisia- tridentata is recorded without cornment.

Valtlablc 2s these studies are, !,ht;y have clew 1,ittle to illum- inate the nature of the cornpeti tive relat-ionships betkleen Artenji sia tridents ta and the gther members of the csrninuni ty , Dr. to es tab1 i sf; the role of the species in the cli;iiax grauslaiid; of the study area.

D. -- Fire Several -instances uf erndicatior, of Frten~jr-;a tridentata by fire have been noted above, ad the "&-illty of the species to survive burn; fig has been repeatedly rt?por?ed f Flc,k-ierd, 1932; Da!~benmire, 1942,

1970, 1975; Yoany ei a: . , i972; !-4c!~t3n, 1973; PI 1 i son, 1960; Loope and

Gruel, 1374). This f?itti,t~has loo :il: ~.heextcxive use of controlled burni ny to suppress "i~especi'es c;n ran5el a& (Pechat-!ec ?.,,rid Stewart, 1944). The hyp0tiies.i~that fire is if central ,importance iri the main- tenance of natural grassland is we]? estabit been co~i;!us iuel y damns 1;u.a ted .

Arten~isia tr-identa. ta is read,i ly ki i14 by fire, and ii.ljst reir,vsde by seed after each SUC~event. Uiiiszrl (196i) attr'ibil+rs,, ... at least part of the post-settlement sagebrmh increase to She sup?resslcn of natural fire, and the reinova'l of the inflammab'le grass urtderstory by heavy grazing. h%iie the ability of fir? to suppress --Artenrisia---

--.--tri denta.ta pop~lla ti ons is clear, the question of whether ~re-settlenient and early settlement fire frequencies were suf ficicrit ti? inaterial ly affect the pupu'lat.icr; size i:s mt. This qi,est.i:!ti will be "created at some 1eng th f n the fol l owi rig chapters.

A1 lelopthy, the i n3i bition of gerrr~inction or growth in other plants by the prod~ctionof toxic chemicals, has been recqnized in recent years tn be pa;?. ~f .the corrpctitive stratel;; of a great many

plants (Rice, ls'r?4) a Al tho!?@ %!?ereSs suhst2ntia7 evsdeace that Artem-isia califorrrica is capabie of chemical suppression of other species (Huller --et a1 . , 196q; %li Zgan, 1975), the cvidence with respect to -Artemisia------t~identata .------. - - is quivocal . Kicd (1954) found evidence that water soluble toxir~sfr~i~~ the leaves of four species of

------Artern-isia, one of which was -Artm:sia------.-tridentata, - - - - were abic to iuhihi t germs'n~tionan? growt!r of a ri;.!!nt,er of te~t.~p..xi.;?s , -i r7c: !id{ ncj -i:rc:m;s .. -. -. . .. --

c: -----i nerini s and A~r-o~~r_-r;-- -. ---.trachycau7-. . -- ... .-- wi. - ... Schla-lCei-er3arid T'isdal 1 j.953)

< , found sonic evidence of a?lelcpathi c cf fects fro;-!! !,ytei?i:;? a f-,r-i~ei;tata litter, but cons-idered the effect too s? ighi to be 0.7 iinport~~ncci;:lde)-, field condi tiorls. Daubsn:i17;re (1(;75) used Field ev-idence to argue that

Artern-Isia tridenta.ta h;?s ix ?ifectSve a1 lelotath ic po-t;e?-,ti51, arici noted -- -. .. --- --. . .- that the sagebr-vsh ur;clt.rs.tory represents 6 r:r~"i*i-!*~

VI . Population Dvnanti cs and he Structure

The age of individual sagebrush plants may be deterinined by counts of annual steni ririgs (Ferguson, 1864) adtkf s feature has bem employed in sever.a"l studies af stand aye struct~m-.--ti~enumbers or proportion of the population in particular age classes. Rwth (1948) exaxined age structures of three stands in Montana, and obxrved a dis- tinct mode in the age class frequencies, dating from about 1910 or 1913.

Poor recruitment, and low class frequencies -roll o-,qirig this period were attributed to th;: effects of gmss compe'ci tion.

Roughton (1972) studied age structure of a number of rangeland shrubs in Colorado, and concl uded that recrui trnent; in Artemisia tridentata is 'natc!ra'l ly irreyular-' . Lonasson (1949) used a combiriation of age structure and long- term (thirty years j direct observation to aszess recrui merit patterns in an old stand of -Artewisi;! .------t;-identata - -- . - ir, Montana. The oldest plants ir: the stand adted frxm about 1885, ?,r?d na ilew recr!~itrnerrtwas observed from 1915 to 1935, during which period stand dens;ties declined due to natural mor'i~li ty . Recrui tmeni: duri rig the pericd 1936 to i945 was at'iusi bt;.kcd .to fawvrah! e (rmspeci f ier!) weather' ccndi tions, ar!d decreased i rr.'-,r.s-spxif i c cornpet; ti oil d~rcto s taod thi tmi rt$.

Dau5cr:rrrirc (1970, 1975) ot?st!?vc=l that ~os:: sZyebrcsh stands in

.washi . ngi;o:;i :c::r1e Even zge!;, arid cor),:l !.ici~i<.thzt i'iGs t piants dated from 51 . t the time of the last fire. He hypothesi zed tnat the disti net n.!odal-ity of age class frequency withir~stands reffectcsd the reiatively riire occurrence of favourabl c! estab'l ishiiient conbi t-io;s .

VI I. Pa! eohtcni cal Studies

AT though -Artexis.i;t.- - pollen tias been reported From a 9rea-t many deposits of Wolcmne sediments, relatively Fw data are available frcm areas pr~esentiydorl,i natec! Ly _Pirtei;ii-- -- s ?; a-- ---tri - - - --ts . The ear i i es t pal y- nologicz? work in the ficle al.ea ~ZStb~t ~f ;-lttqsen (1355) but

Artemisia-- . pol i cl;s were r~ct tiisti~;g:*is!redi r: $I]is ~i~dy. Bright (1966) prodilced a pollen ciiagram frun a s5tc in south-

eastern Idaho, covcri ng rmr;L; o-: ;he !lo1 r~ceriepwi oil .. Art~rnisiAC: po l: er; is present at the sot to^ cf the ~rof-i!~.fladixarbon dated st abxi

12,03C years h.P. Bright c!sn~n,en",d 3,: ih? hdL that there is no detect- able increase in Prteiiiisi~"crllcti in the upp~~rmost, recent part of the profile, and that this dppw;-'eCl tr3 cotit'i"zc!i~I-". . . the opinior; that the widespread di s tr-i buti xi of tile shrubby speci'es of Arteriisia is the resul i; of over~!-dring a~';r,teiaf~renr,e by man. ''

Ander;or; (1973) pr-2: ?n:>~! a po'i 1 cr, djigi.881 from OSCJ~DUSLake, within the study area. i!,d da:,-; are dtrived frm analysis of a short core in the surface lzkebcttwi sedinents. No &t?s were obtajned, but

P,nderson bgl i eved that tt:e core covered most of the nis toric period.

ila ta are apcarent:ly 1n.i ssi ng . Alley (1976) has presented a pollen diagram from a site near

Kelowna, just north of the field area. Artemisia is poorly represented over most of the length of the core, but shows a prominent peak at depth. The zone commences well after a radiocarbon date of 8,140 years B.P.--perhaps 7,500 years ago--and ends shortly after being interrupted by a stratum of volcanic tephra from the Mt. Mazama eruption of 6,600 years B.P. It was on the basis of these high Artemisia levels, as well as a corresponding peak in Gramineae, that Alley inferred Hypsithermal condi tions at this time. Above this zone, the record of Artemisia is spotty, and there is no clear evidence of a recent increase. However, the upper 5 cm. of the core were discarded. There is an increase in the abundance of Grami neae pollen in the upper part of the core, suggesting an increase in the area of natural grassland in this part of the valley

during the past one to two thousand years, but this increase is not paralleled by a corresponding increase in Artemisia. These studies do not appear to support the proposition that Artemisia tridentata is part of a grazing disclimax in this area. If Artemisia tridentata was present in this area through much of the Holocene at densities as great as those of the present day, it is necessary to account for the widespread impression of recent invasion. Alternatively, the invasion may have taken place, and interpretation of the pollen evidence may be in error. The most probable source of such error lies in the realm of pollen taxonomy, for there are several species of Artemisia in the area, and the Artemisia grains recorded in these studies may not derive entirely, or even principally from Artemisia tridentata. Even if this speculation is correct, however, and most of the pre-settlement Artemisia pol len cmes fron: :;g:xics other than

--Artemis-ia -- -- -tridentata,.. - the species most prrobal?lj involved, Artmi s.i?.

-trbaarti ta and Artemisia -frigid~ are t.hernse?ves either shrirhs Gr prominent perenniai herbs whose abundant preseiicc! carlnol; readily be reconciled with the commonly hypothesized 'virgin grassland'. These problems, including pol 1en taxono:ny within 5he genus and the t$jm of environmental change which might lead to a shift in species dominance, are treated in subsequent cha~tzrs. The purpose af this chapter is .to descrihc the invesi.fgat.ions

2 tridcntata in which were undertakerl cn the preserit -Artmisi - - - - . .- -.- -- ~,~?ulatior-r the study area. The principdl objective of t!?ese investigations was to identify those factgrs which control -Artemisia- -- -trj?entat,a------ratye and density at the present time, and whxe v.?!iatioi~.;ver t.irrie ci3.y have resulted in changes of populat5~nsize. On the bdsis of fkexisting

1i terature, and prel imi nary fio ! d observations , the research was f ocrised on four potential mechanisms of population contrcl:

(1) Clirniatic---- fact~rs--The present population in this ?re&is largely confird to the \la1 ley hottors, apparertly by unfi,v~urilble c'ljmatic conditions at higher elcva ticti.. If the specific cl im=t;ic cletnenls i nilolve;! can be icier:ti f-red, th;l probat1 e irnpac t of cl in~dtic change on "Lhe species range and density might i)c es tir,~atcd.

(2) ---.-Inter-=J ----Afic com~~t; ---a-i tion--A1 - %hou;!i competition fronl perennial srasses hiis been advanced sc, c factor control 1 i ng Ar?cmi:sici- triggntata ramp and dens? ty (Chapter ZII), no clear demonstra-cion of the relevant ~-rechan.ismhas yet been n~adc. The demonstration of such competitive control , and the identi f icat,io? of the rricchani sm i~il01 ved would permit some evaluation of the sensitivity of the populntiun to

changes in grass competition. Such changes in corrlpeti tion may rsesult from overgrazing, cr other causes.

(3) ----Intra-snzcific cor~lpetitiorl--Pi.escnt p3pnlat-iot-I dens7: ties may be limited by sbppression of seedlings by the established population. Although such suppression is unlikely to have directly deterrrlirred changes

in range or density in the past, it may influence present rlensi ties or account for the irregular reproductive pa?-.terns described by Roughton (1972) and Booth (1348).

(4) -Fire--Although-- fire is not now a,~importarit deterirlimnt of

--Artemisia -tridetitafa ------range or dcnsi ty -in this art.5, it may brave been so in the past before the introduction of sysicrnatic Fire suppression. Cha~gesin regional fire frcqueiicy are trcdted ir! subsequent chapters. The focus in this chapter is the ecclogical chal~gswhich rc"s.ult from burning stands of Artemisia-- -trickntata.- - -- -

I 1. ------Research Stra tg-

Any explanation of the present range and density of the

Artemisia-- ---.tr-ide~tata -- pspr~: atiun in this area, and any expl anzti on of past changes in thatppopula-?ion, must r;xl:e reference to the factors which control popui at'l OK r-eproducti on a:-id iii~~ki'ii ty fa!.. a stable population impl i cs a dyriamf c equi 1i bri ~!i!betweel? rewoducti on and mortality, while ppulaticn char~geimpl ies 8 departure from that equi 1i bri um, a ptrri od of di seqlii 1i bri ~ri-il, 2nd pcrhips the es tabi i s hinsnt of a new equi ii tr3 un; cortdi tion. St~hchanc;~; i:it,s t rLesult froin changes

in reproductic;n, mortal i iy , cr both. 'To the ex t?r:t that reprodocti on and mortality are determined by environmental factors, the reproduction-- mortality equilibrium is the operational and dynamic equivalent of the environment--population equilibrium discussed in Chapter I. Environmental changes may affect both the reproduction and mortality rates within the population, but variation in reproductive success has generally been assumed to be more variable, and thus more important in producing changes in population size and distribution (Roughton, 1972; Payette, 1976). Mortal i ty patterns in long-1 ived perennials have usually been found to be relatively stable--i.e. morta- lity rates are either constant or change systematically as the plant ages (Hett, 1971; Hett and toucks, 1976; van Valen, 1975), and in general the assumption appears to be a reasonable one. The process of recruitment to a plant population has been summarized by Harper and White (1970) in the form of a schematic model in which a set of environ- mental 'sieves' remove incremental portions of an initial seed cohort at various subsequent life stages. The sieves may represent environmental factors such as weather conditions, seed predation, or competitive factors. The plant losses which these factors effect are cumulative within a given cohort, and may vary in time and space according to the - environmental conditions prevai 1i ng , resul ti ng i n correspondi ng varia- tions in recruitment success. In accordance with these ideas, the research described in this chapter has focused on the recruitment process in Artemisia tridentata, except in the case of fire, which is primarily an agent of adult morta- lity. In doing so, it was initially assumed that adult mortality was relatively stable in the absence of fire, and that most recent population 57 changes and much of the present varidtion in population de,~sity \ids due to temporal and spatial variations in recruitment success. The val idi ty of this assimptfon is examined in Section 111. If this assumption is substantially correct, recrui trnent success m2y be exarni ned in several dif ferer;i: ways. Present plant dmsi ty pro- vides an integrated index of relative recrui tn~entsuccess in the recent past. Densities in different situations may be compared, and inferences made about the effect of cnvironnlental diffsrences on past recruitment success. The method is stren~thenedif the cijrnparisons can be lirnitcd to similar restricted age grouas (see for example, horn 3971, p. 39). This approach has been used in this study to investigate the effects of grazing disturbsnce, by comparing densities on grazed and ungrased sites, and the effect of jntra-specific co~petition by cclnparing seed- 1ing densities under di fferent adul t densi t.y conditions . Density corn- parisons have also been used to cxarnine adult mortality resulting from fire. More detailed measures of temporal variation in recruitment success may be obtsined from direct monitoring of the population for seed production and seedling rrlortali ty, cither in tha fieid or under control led laboratory concli tions. Fie1 d r11on.itori ng oftm pi-ovicies detailed and reliable data but is usually possii)l;. or~?yfor l'rnited time periods, and thus samples only a iimi ted ra:ige of the potential environmental variation. Eeca~seth~ climatic environnect, was kno!m to vary widely over extended time periods, this approach was rejected as unsuitable. A wide variety of ewir-urmentzl conditions inay he simulate3 in the laboratory, and the ef%cts of reinyle e~vironwnLa1 factors may then be is01ated. Pk,i s ej-zen {lsed

to examine the effect of grass co~pctitioncul --Arteaiisia -. - - -.tridentata -. -- seed: ings, and to test for the effect~of .I: nt!-a-sp,xifir: co~l~~ti-tion.

Past variation in I-ecruitment scicccss may he inferred frm the

age structure of the existinc, r~cpulat-ion. If the assump.tio:i of stable adult mortality is correct, the numbers of plants in particular age classes in .the populaticn should reflect the clcyree of recru-itrnant sriccess

at the time of dni tiation of those iigr classec. :f such a series of age class frequencies can be corrected for the effects of adult, mortality,

a quantitative index of past recr~ritrnen",~~~~~~.'~~.wj'l? sl. Such an

i~dexis analogous to the more familiar indices of tree ring widih,

corrected for the dccl ino in riny wjdth which accoir:psnies advancSnrj tree age. As in the case of ?:rw rf ixlice., the corrected ;ige class w'lries may be used l:n an analysis tc: determine the effect of past erwironmental variations, if these are knoxn jc;ee for exampie, FY! tts et- . sl.,. .- -. 1971).

The need to correct for adult n~ori;aIiiy is a serious weakwss of this procedure, for past m~rtality yates are cii f'f i cul t to deter111-lne, but several models of morta?ity in perennial plant populations are now available (Dewey, 1947; Hett arid Loucks , 1976). -he p-4 nci pal advantage of the method is the opportucity to eica!il*ne an extended record of recru i tment success under f3 el 6 condi ?,ions . ?ccwi trnerlt records der-i ved from the regional popu l2ticn ays structure have Seen used tc examine the effects of climatic control on vecruittnent si:ccess, and indircctly, to

examine the effect of cornpe l.itSai on seed1 i mj survival . Section III below de;cr iles Ihc sacip-i c rrcr~dlicl? the regional age structure was derjved. In adcii Lion to pvw; di17s ckta or, age class frequencies within the population, the sample yicl (id ctiita ori pl dqt densi ty , and was str?teified to permi t compa t-ison of grazed and i~i;grazcd stands. Thesz d;l ta have been cvployeci in 5cctions IV, V and VI to examine the effects of climate and competitiori on :-eproductfve saccess, and have bcen suppl enentad with further iief d or experimental dat.a, where r,ecessary. The origins of these further da La, and of the data used to exanline the effects of fire, wi 11 be treated in the appropriate sections .

III, --Population Age Stl-uct::i-e in --Arteniisia tridentdta

A. Method

The sarnpl e from which popul s ti on age 5 truct;ure was determi neti was desigr;ed -lo fulfill three requirements: to provide a profile of the age structure of the krten~isia-- tridentati? population within the study area, to prcvide data by which 2rQazeciad ungrazed stands might be cornpared in terms of age str?ici!~reand density, and to assess the impact of grass competi tior! 01-1 recent recruitment. \.ii ti~ir, Artemisia tridentata stands. The sa??piewas desi yxxi to cover a nwher of stands at differant elev'ations, from ~'a!ley buttoin 1.9 the pr'esect range limit, a11d t.u include thveil s'ites wh'ict! ww knwa to have bcen I-eceritly pro- tected from grazi ng, and three ail.jace;:"i Si t.e5 wh': ch liar! recently been subject to grazing disturbance, A ?~-c",::mitizry smple iri the fall of 1973 (Sites P, and B, iate:- con:!:iwd as S-itc- A) d~mnstratxithat the poptrf atifin age st;ruc.t;tr!-e was f i*~*e~u;zr, wf.t.k son;:- a9e groups much more frequent than othe:-5, al?d therefore .tii3",

and topography, separated from adjace~;.l stands by chiingi:~ ir, r;uSst;rate

Gi- topography, by fertce li nes which wight i:i:pl.:/ sow differtr~cc;f n

grazi rlg hi story, or. by marked changes in Artmiisia tr-identat;;-- . si ze or

densi ty . Sarnp? i ng was confined to 1eve' , we1 ? - dra ined sul-f aces to r11; ni - mize the effect of slope, aspect and soil type, and t.c stands which

showed no evident::, of recerrt, severe ailul t ~r~ortaii ty. S-i tes D, 9, and

K were ungrazed, ;ria were paired with griized Sites E, J, and A, respec-

tively. Grazed Sites C and G were chosen as representat;ve of range

edge coidi tions, and cpzed Site F was -: ocatcd at an i :~tewc!d-iat;eelejta-

tion Oetwecn Sf tes E aiid G. Stand location is shown in Figure 4.1

On the basis of' the i~itia;sample, it ws estimated that a r~inirnunof about ICO stcn~sf'roiii tach st.;lud wuld b? ..necessary to acie- quateiy characteri ze stand zgc. ~-irti~tttre,The sairrpl i ng was ?e:-formed by cutting all plants within a seri5s of random quadrats, and rctaini ng a basal stern seg~entfroin each fcr later age: determination, +~ziArat sizes of two metres and three metres square were employed, &pending on stand density, so that between sewn axi fifteen quadrats were enumerated in each stand. Quddrats were ?:xatetl by a 'random walk' procedure, illustrated in Figure 4.2. In low density stands the quadrat sample was augrnerited by a furthw callec-tior; of stein segments chosen by a random quarter-pci ~t procedure (Griecj-SmE .ti;, !!%4). The total samplc cor,sisted of 85 quadrais Sn nine stands, and a tot51 of 1,276 individual stems.

The numbers of other shi-ub species were ;?:so recotxle2. Standing herb bioriiass was estimated by clipping and we.ig!!ing

The results of the sample, o!? a qu.ilt.at--by-qt~;ld5~~t his-!~, are

given in Appendix II. Age structure; a-t: i-ndiv;dva'i sitc, ai-o sI;awi~ in

Figure 4.3, and dcnsi ty, 0th~~shrub derisi ty, hevb bicj:lirzss, irid levati ti on

data zt-e shown in Table I!!. 1. Each year's aye frequency is show as a

percentage of the total sanple at th3t site. Tke regio~alage structure

(Fig. 4.4) was deterwined by astera??'ngthe p~rwtita~eva !cw for all

sites except Site K, which was very small, and yi2lded osly a very small

sample, well below the 100 stems set as the mn?inal ~n-!niw~:n. Each s-i te

d thirty and forty-flvc year ; (sf age, hnci unothrr b?r,~~cn 2'i,.i;: ?cur ;;;d ridR twenty years. These modes are inierspersed with pet- icds of v:4r>r- j *;j , ' representation, from about 1944 to 1954, and dbclut 1'370 to Y/'+. , ,!$ a* r[ m A? though there i.; subs tar~t.i.a?si te- to-si $r? variation, rr~iist. stands shcv! F P the main features of this patr.cri1, particular7y th? high recru-i twnt phase irl the late lfJW1s. Sclne af the var-iacian hc-twezti sites mi; Se due to sniall sa:i:plc size; nmt of the yo:lnqcs-r: plants in tile r;zlr;p7ie 24,

Site H were fou~din a single quadrat. Nost of the su5sequctit ac3:ysi; has therefore been performed on pooled data sets, ir, order tc achiede greater statistical sfabili ty. A1 tllcdgh fire (Daubenlnire, 1975). insects (Yourig et a1 . , 1972), rodent damage (@ueggler, i9671, and drought (E I1ison and Woolfol k, 1937)

have all been cited as causes of mortality ~n inarure Artxi-isia- --tri-

-dentr~ta- -- , none of these inc.cn3ni sirs would rr'!3i~icsmb? c of sel c;ct i vcly Site . I?-LZ .r"l -< m1.v st- .r. X &-' t/m a:, E 't-o rentovirq partrcu:;li- adul t acp CJI'OL~~S, ihj7i" leaving a6jacerlt aye groups behind, nor of doi ng so syncl':rcr!c~~s?yover 2i.I cxtl5ntlcd arm. Si:~iilarly , only recruitment fd-i 1 :we can ~ccGL;~!~For thc zoir~~lztcz'ssel.ic? of first year seedlings in the sample. It inay b;l: cc~xludadtkat liiQSZ: cf the observed varia~ccin rotmrt at;urdaricr rcs~rl'is frws irc7ri~.i:ion -in recruit- ment success, rather than adu'l t nmtai i ty: and .chat the orsg'inal assumption of stable !nortai ity patt.er;~snzlj i~cacceptsd. Iiowever, adult mortality 2r i.ecent 'Ir,vas-!or In;.!! accwnt -'or the absence of very old plants at sonic s-ites, and actual mrta?i.tj~*i.?tes may net be as high as these dam ilnply.

of ishment C. -Derivation -- the-- -- Est2b:-- -- .. -- .-- -Record .. -. . - - In ordzr to extract frm thest? ii9c s;".ructr~i>edata, an index of past recruitment srrtcess wh-ich fs co::;parab'lr:- bi?t\~:'i?t?d4.?1:?.;i"~nt as@ groups, it was necessary to correct the raic age class yroprt-icns for the general decline in frqucncj w-i th c'las:; zge \ciiic;h results from mortality wi thi r? the poptlat-ioi-!. FoI1 owing the ay,proach of Deevey

(1947) and of Hett ard Loucks (197'6), t!,is c.crrx+:!'on was performed by fitting curves re1 ati ilg age class 1'w!:!~r1cyKO cl tiss ase, a!td uzf ng the residuals from those ciiwcs a5 ~h;?\*ccjuirf?d ;-ccruittaent indices. Two models appe2r appropriate tor this purpose. The Firs!; (Model 1) posf;u- lates that the le~arithmof cf ass Freq~e~cyis a 1 inear fcnction of class age, implying that the prr~babilityof mortaljty is cmstarit with acjt?.

The second (flciciel XI relates the iogaritt'!rr: of class frequency to the logarithm 0f class aye, and ic1lilii.s ihi; t:ie pvcbability of death decreases wi th acivanci RCJ age. P,l thoi!(r,i;?these rela tiocsbi ps were or'gi n- ally propcsed as rr.,ode;s of mortalit.zr ip s';i-:b!e popirlaticris (tiett 811d Loucks, 1976), this narrow interpretation is not vaifci ji7 this case, for the population age structure is manifestly unstable, and dny fitted curve will reflect not only mortality but also any recent population increase or invasion which mzy have occurred. In this study these models have been used to remove the most obvi~ustemporal trend from the data, much of which is due to normal morta1it.y withirl the popu~a%ion,but some of which may be due to ether calises such as catast.rophic t~io~talityby fire, or rccmt population increase due to invasion.

Figures 4.5 arrd 4.6 show these two curves fitted to the pooled age class frequency data. Goth models yield correlation coefficients significant at the .01 prob3bili.l-y lev21 , and may be considered to pro- vide a satisfactory 'fi ti to the observed data. A1 though the models enibody different assumption: about the piittern rtf' moytal i ty in the population, there are not at. present any s trorg groutds for adopting oce over the other as a means of correcting the age structl~reseries for the effects of mortality. It was, therefore, decided to employ both models as a1 terna.tive correction schemes. The residuals fro^ these mortality mode7s form the recruitment indices used in subsequmt analysis (Section V). In the case ~f ilodel I, these residuals were found to have non-ho~ogeneous variance, and were subjected to a norr~ializingtransformlion of the fwn~Y-RiE where Y is the transformed vzrishle, E is the expected age class freq12ncy given by the mortality model, and K is the residiral from that estimate. In the case of Model 11, this problem did not arise, arld the residuals were extracted as the first step in the analysis.

It was hypothesized that if the ohzerved vdriaticrns in ?stab- lish~~eritsuccess Nere due to variations of c1 inate or other eiwironmenta?

conditions at the tfme of estziblishment, it would bc possiblc to obtain significant correlations between the es lab1 ishinerrt indices and approp-

riate environmental records. Such currelations should serve to identify

the environmental variables involved, anc! to prov-ide sow measur-e of

their relative iiyortancc iri det.emi ni ng recruitment success i n PA--Artemisia tri dentata . The envi ronmcntal fsctors chosen for this analysis were those related to the regiorta: clknate, as described in Secti~nV. Before proceedi ny with this analysis, the role of i nter-specific corripeti tion is exarc-i ned in order that these res~ilts mi yht be i ntecya ted wi th the analysis of climatic effects.

A. jrnJrodw3ion Two hypolheses have been advanced to explc.?n thc increase in

--Artemisia -triderltata density which way result from grazing disturbance.

The First is that ,4rtefi;isi~------tr'detltat; .------seedlings xn~et?with esi-abl ished grasses for soil moisture, and that grazing reduces the hater demand of

the grasses and increases -Arterllisia --tridenf-am sedling survival (Booth,

1948; Johnson, 19"). The principle objection to this hypothesis in this area is thdt Artemisia gidentata is cownonly absent from those

mesic situations in which .chis form of conipet-ition sho~lldbe last.

The relationship between ixoistur-2 availability and recruitment success -- 'Is treated in the section or, cfinxitic effects. r he second hypoth-?sis is that Arternisia trid~ntatarequires bare mineral soi 1 seedbeds for successful germi naticn arid growth, and that grazing disturbance increases

---Artemisia tridentata- densities by increasing the supply of such micro- sites (Johnson, 1958; Johnson and Payne, 1968).

The failure of the aye structure sample to provide da.ta suitable for testing this hypothesis led to the adoption of an experin~ental approach in which germinatim and seedling survival were examined under differing conditions of bare soil microsi te availabi 1i ty. This experi- ment is described in Subsection B belmi. Subsection C examines the effect of grazing on reproductive success under recznt field conditions, using the grazed-ungrazed replicates fro^ the age structure sample. Subsection D exami ncs other possible controls on bare soi 1 microsi te availabil jty, end attempts to show that, some portior, of the existing population age s truct~remay be a consequence of past variations in this corrdi tion.

B. --An E~erirr~cnial-- Stue of Grass Ccmpetition The purpose of this experiment was to evaluate the effects of bare mineral sci 1 microsi te qreqdcncy on ger~inctionand subsequent growth in Artenifsia --tridentata. -. Seeds gathered iti the fall of 2975 were sown in the laboratory under conditions intended to siinulat~three levels of grass connetition and nicrosite availability. The three seed- lirig populations were cospilred for gerniination rate, seedling survival, and seedling growth rate.

(a) Method Sods were cut f;-on an o;)en, grass covered area in the ungrazed stand at Site H in the late surliii.ei. of 1975, prior to the production of the --Artenisia --tridcntata ------seed crop. The sods were ccrnposed of Aqropyron - 4. spicatum,- with an understory of moss (Tortula cf. rural is) and a); uniden-

tified Ifchon. The sods rrere tsl:e:i from a small area free of --Artemisia tridentata, and were chosen for their high degree of ground cover. The sods were c.ct tc fit plastic pts 8 crc. square, and were then classified and scarified to produce thw levels of ground cover--near total cover, an intermediate class c~itb abouc 50 percent bare soil, and totdl bare soi 1. Tkpots were sown in December vith 25 -A\-temisia -tridentat? -- seeds each. The seeds were so vn throiigh a p7 6s tic tcnp'i ate, with holes in a five by five grid so that each seed and seedling could be identjfied by location. There were six pots in each treatment, and a further ten unsown replicates as a check on viable seed residual froiri previous seasons. The ?ots were rr~oisterw! from bolo!.: an3 held ill a darkened refrigerator for 31 day5 6.t ;err) wgrees C. They were then removed to an incihator se~for an eight-hour photoperiod, with a maxinium daytime temperature of 20 degrees C. and a minimum night temperature of 8 degrees C. I1 l umiiiation at the soil surface was app\xximately i ,250-foot candles or 13,455 lux. Germination (radicie emergence) was observed on the day following the start of incubaticn. Plants were cour~tedeach day for the first seven dzys, and at two and three daj intervals thereafter-, for a period of 56 days. 1he pots were keu t we ll waterxi. At the end of the experiment, the plants were cut at the soil surface, pressed, and the air dry weight recorded.

(b) -Results-- -- and-- - Disciission--

The resul ts are shown in F-i~ure 4.7 and 5 !I Tab1 es IV. 2 and

N.3. A11 of the seeds in the bar.? sdi1 treatn~entgerc~inated, as against

TABLE IV.2

Germinatior; of Artemis-ia- .- - - tridmtata,------.-.-. at Three Levels of Grass and Littsr Cover

Rep1 i cate Sod Intem~ediats Bare Soi 1 c/ # # /o --- X -- -- -. -. - -# %

TABLE IV.3

G~rmination and Seedl i ng Survival in ---Artemisia tridentata, at I-hree Levels of Grass and Litter Ccver

Rep1 icate Sod Intermediate Bare Soil iF Sd_ # '% -# X in the intermediate tri.at!r.c-nt and 70 percent in the urtclisturbed sod. As the seeds were merely dropped upon the surTace, and the standing grass rnateriz! had been clipped before sowing, these d-ifferences are ~otbe1 ieved to reflect differences in i11 umi nation betweerl the treatnents. Gerrd nation was virtudl ly complete by the eleventh day from the start of the incubation period. Seedling morta- lity ir! the sod treafment was observed after six days, and by the seventee~thday the number of plants had been reduced to 12.5 percent of the seed input. SimSlar, but lower mortality was observed in the intermediate treatment, while mortality in the bare soil treatment was very low. k few plants showed syniptorns c.f attack by a 'damping off' fungus, but in most cases death was preceded by blackenf ng and necrosis of the cotyledon.;. Most died before true leaves were produced.

The pats were kept we71 watered, and mnis ture competition may be diimissed as a cuntr;outory fdctor. Although the pots were watered from the bottom, a practice which should have tended to zonceiitrate soluble nutrients in the upper layers of the soii, the symptoms of the seedlings sugyes t a mineral deficiency, perhaps phosphorus or nitrogen. This hypothesis is supported by the data shown in Figure 4.8, in which the total standing bioriiass of Artenisia--- tride~tataseedlings is shown as a - function of the pH of the surface soil. here is a significant positive relationship between total plant weight and pH, in the range from pH 5.4 ta pH 6.5. There was no significant difference between mean plant weight in the treatr~ents, and the total weight data reflect plant ni;r,,tc?r rather than plar;t size. Lm pH in the sod treatments is probably

Suc to the influence of the grass ii~ter. Phosphcrus has been shown to Bare Soil o Interrr~ediate D Sad

Fig. 4.8 - Total weight of Artemisia ---tridentata standing biomass 8s a function of pH of surface soi 1. Weight values reflect seedl iny survivorship. be most available at about pH 6.5, and to decline with greater acidity due to the forination of insoluble compounds of iron and aluminum (Black, 1957; Eucklnan arid Brady, l96O), ard the symptoms of phosphorus defici- ency may stern frorn this source. The reduced germi~ationin the sod treatrnen ts niay resel t from a1 lelopathic srrppressi~n. Schlatterer and Tisdale (1965) tia\~ereported some evidence of germi natioti inhibition from the litter of an unidentified species of --Tortula. It may be concluded that bare ,nineral soil microsites do improve germinatf on and establ ishent success in Artemisia trjdentata, and that the absence of such sites may severely lin~itestablishment. Seedling establ ishment under field cortdi tions appcars to reflect the availabi 1i ty of such microsit2s. Rodent castings and cow path edges often support high seedling densjtics, or higher densities of mature piants. All of the 25 or 30 seedlings found in an intensive search of a small area near White Lake in 1376 were rooted in patches of bare mineral soil. Some examples are shown in Figures 4.9, 4.10 and 4.11.

C. Field Strndies of Grazing Effects The importanct. of bare min2ral soil microsit~sin the successful estab'l ?shn~er:tof s\rtmisi a tridentata provides a mechanism by which overgrazing, or other fcrm cf disturbafice, might be expected to improve reprcductive success and lead to increased plant densities. The question of whether overgrazing is the primary source of such microsi tes and is thus a prerequisite to --Artem.is-ia tridentata- establish.irrent in this area remains. Ari answer to this ques tiorr has Swn sought first by comparing grazed and unyrazcd stands in terms of age st!*ucture and density, and Figs. 4.9 and 4.10 - Arternisia- tridentata-.- seedlings on bare mineral soil sites. The seedlings in the upper photo are yern~inatirig on the casting of a small rodent burrow. Those in the lower photo are on a spoil bank. Fig. 4.11 - Arteniisia-- __iridentata seed1 ings in a patch of bare mineral soil at Site G. 8 2 second, by attenipting to measure the abundance fif b~rcsoil sites in ungrazed areas. The age structure sample was designed to include ihree pairs of adjacent grazed and ungrazed siands, divided by fencelines. At site pair A/K the feweline could !)e dated to 1964, i ndicat!ng ten years of differun.tia1 treztinent at t'7e time of sampling. No fir^ dates were avai lab1 e for the other fence1 i nes, but 1ocal 1andowners i tidica ted that grazing protection had continued for at least ten years, and possibly as long as twenty. it was hypott,esi zed that if the increase in ab~indance of bare soil microsites caused by grazing is critical for sagebrush establ f shmmt, plarits under ten years of age should be significantly more dense on the grazed st tes than on the adjacent ungrazed si tes. Data from the three pairs of sites were pooled to form a si ngie grazed and a single ungrazed populatioti. These data were derived from the age structure sample in the form of quadrat densities uf plants ten years old and crnder, and were examined for diff~rencesin mean density between the grazed an3 ungrazed populations. Because the pooled distri- butions tended to be mu1 ti-modal , the test was nade using the non- parametric Mann-Wlii tnq U statistic (Siege1 , 1956). Densities of plants ten years old and und~rwere found to he slightly higher in the grazed stands (.468 plants per square metre) than in the protected stands (.332), but the differences were not significant (i equcls 1.075). The fr2quencj1 of young plants was found t~ be slightly greater in the protected stands (.48) than in the gr2zed arms (.44). Grazirg disturbance does not seem to have significantly increased the density of recruitme!~tin these starlis daring the past ten years. However, .total h*temisia ----tridentata density is sign-ificantly greater in the srazed stands than in the pro- tected stands (7. eqiials 3.26, p less than .002), and this difference may reflect grazing hjstory prior to the geriod for which protection is certain.

The faif uv? of grazing to produce s significant i11crea.se in recrul't!~:ent dewity during the past ten years rnay be due to intervening factors, such as unfavcurabie climatic conditions, or suppression by the older -Arternis.ia --tridentata p.~pulation,as discussed in the fol lowins sections. Becal,rse of these unceu.taint3esY it would seem unwise to dis- miss the possib i 1 ity that grazirig distui-tance may i:ncrease sagebrush dens-it:l es by < nc:.~-asing the avai lab!*i i ty of bare soil microsi tes. However, it would appmr that grazing disturb.;~ce is not a necessary condi tjon fcr. successfu: sagebrush establishment ;n this area, for there is Clear eviclcnce tl~t:.c?prcdilctior~ in uqrazed stands has continued at rates close t3 tiwse cF.scrved el seullhere. These results suggest the existence of a moderate supply of bare soii micrositt?~!'?-I irngrdzed stands, at '!east during the last deca.de.

Measureme~ts of the area covered by such microsites in ungrazed stands yielded the r.es~7t.ssitown ii: 'Table iV.4. The data were derived from a series of point sa~r;p?esspaced at iO cm. intervals a1or:g tramects thrcugh the stands. The stand at Richter Mountain had been cleared of

----Arten2isia tridentat3... - by fire -in the previous year, while in that at White Lc:ke the s;lgefiwsh had been suppressed by periodic clipping . Bare soil com'i-i iuies 36 and 64 percent of the total cover in -- the two star~ds. i hc differences appear to be due largely to the reduc- tion of litter cover by ?.ire at the Richter Mountain site. The values TABLE IV.4

Grass Cover Values on Ungrazed Sites

Poi nts Percentage Soil Grass Litter Soil Grass Litter

Rich ter 131 52 21 64.2 25.5 10.3

White Lake 112 63 134 36.2 20.4 43.4

are comparable to the 40 to 50 percent bare soil cover reported by

Tisdale et al. (1965) from an undisturbed Artemisia tridentata - Aqrop.yron spicatum - Festuca idahoensis community in Idaho, and appear adequate to ensure recruitment sufficient for population growth and maintenance if other factors are favourable. Again, it may be concluded that provision of bare soil microsites by grazing disturbance is not a necessary condi- tion for Artemisia tridentata recruitment in this area.

D. Other Controls on Microsi te Availability

The availability of bare soil microsites may be determined by factors other than grazing or rodent disturbance. Agropyron spicatum tends to become rhizomatous under more mesi c conditions (Hi tchcock et a1 . , 19 55), resul ti ng in reduced proportions of bare soi 1 (Stoddart, 1941) , and drought has been shown to drastically reduce the cover of many grassland communities (Weaver and A1 bertson, 1939; Tomanek and Hul ett,

1970). The measurements of bare soil cover described above were made after a series of relatively dry years, and may, therefore, be abnormally high. Such direct effects of drought stress may be increased, on grazed areas, by close cropping and increased disturbance during periods of

drought and low forage production. Accordingly, we mic~htexpect that

periods of i ricreased -Artemisia -- tr.identata reproducti on ciould show some correlation with per-iods of increased drought stress, subject perhaps tc some Sag while the grass cover responds to the changi~ymoisxurc environment. This hypothesis was tested using the data shown in Figure 4.12. The solid line shows the artnuai water. deficl't frjr Keremeos, smo~thedby a seveir-year running mar to siniulate r121atively long-term changes in the moisture enviro~mentarid to t!cccmn~odate the possibility of &lay& response from the grass community. The derjvation of these water deficit

values is treated in Section V. The two rows of symbols along the

abscissa are derlved from rigwes 4.5 dnd 4.6 in Section 111 above, and represent years in which recruitment success was greater than average,

i .e. years of positive deviations frm the two r!iortality models. The

water deficit values k!ere converted to 2 series of positive and negative deviations about their own mean, al:ot.ling the two sets of deviations to be compared by means of a simple sign test (Siegel, 1956). If an association exists hetween reproductive periods 2nd drought periods, psitive reprcducti ve deviations should be paired wi th posi tive water

deficit deviations (and negative with negativ2) more frequently than would be expected by chance alcne. The results are shown in Table IV.5.

TABLE TV.5 Test of Association Between Periods of Drought and Arteniisia------tridentata- Establishment Deviations in Deviations i n Bi nomial Sariif! Direction -Gpete Direction Probabi 1i ty Mortality Model I 2 9 16 .036* Mortal i ty Modci I I 3 1 14 .008** "Significant at the 52 level . **Significant at the 1%level. Deviations in sim! lar directions pair tilore frequently than would be expected by chance alone, and the hypothesis that an association exists between drought periods and periods of increased Artemisia trjden - ta -- ta - reproduction may be accepted. The mechani sni i nvo? ved is probably an increase Sn the frequency of bare soi 1 micros-i tes during periods of drought stress. This mechanism may also play some part in res tri cti ny Artenisia-- .tri'dentata- - - -- to the driest portions of the study area.

V. -Direct Climatic- Ccrntrols on -----Recruitment Success

A. -introduction Of the various environmental factors vhich have been proposed as controls on --Artemisia - - tridentata-- range and density, only those associated with tk regicnal cl ima te appear to be capable of suppressing reproduction simultaneously at a number of dispersed sites in the manner suggested by the age structure sarcple. Climatic effects may be indirect, through control of the cumpeiitive environment as hypothesized in Section IV, or may directly affect such physiological processes as seed production, gez,ii rr~tic~n,st~:dl iny grodth, dnd seed1 i ng survival .. The purpose of this section is to present evidence for the existence of such direct controls, and to identify th;! cl imztic elen~entsand mechanisms which appear to be involved. The procedure adopted bas been to search fcr siynificant cort elations between particular climatic elements and recruitment indices deriv2d from the rcg ional population age structure, under the assu:~lption xh5 t the ex-i s tence of such correlations provides at least przswptive evidence of th,e existence of a cause and effect relationship. The following subsections deal w.i th the choice cf potenti a1 cl imatic controls (the independent variables), the structure of the analytic procedure used, the results of the analysis, the eco- logical interpretation of those results, and an attempted validation of thse results by cort~parisonwith the present spatial distribution of the species .

8. -- Derivation of the Independent Variables---

The a1 titudinal range limit reached by -Artemisia------tridentzta in the field area at the present time appears to be climatically induced, and a first hypothesis was that those clirnatic factors which restrict the present spatial distr;btitim of the species might also be responsible for some portion of the observed temporal variation in recruitment success. By analcgy with the present spatial distribution, it was expected that those years in which weather patterns were similar to the average conditions at low elevations would show higher indices of recruitment success than years in which conditions were similar to the averages at high elevations. This analogy between spat ia: and tcinuorai pr~cessesserves to define the expected directicn of any climatic controis, but is of little help in isolating the important climatic elements, for there are few features of the r=gionaf climate which do not vary with elevation in this area. 60th tenperature and moisture conditions appeared to be potentially inportant. Low spring temperatures (Harni ss and McDonough , 1975), summer drought (Johnson and Payne, 1968) and low winter temper- atures (Marchdnd, 1966) have been suggested as causes of reduced growth or seed7 i nr; mortality in ---Artemisia tri:dertta ~a,but 1i-ttle supporti r~g evidence linking such factors to actual recruitment failure has been

avai 1able.

In the absence of clearer hypotheses about the details of

climatic control, the analysis was performed by specifying a large

number of potential climatic predictors, and selecting from those the

elements which showed significant temporal correlation with the estab-

I lishment indices derived from the age structure sample. The initial

data set included the twelve monthly values for each of temperature,

precipitation, actual evapotranspiration (AE) and moisture deficit (D).

These 48 variables were subsequently reduced to 42 by excluding the

December and January AE estimates, and the November, December, January

and February estimates of D, all of which contained many zero values,

and closely ref1 ected temperature conditions during the cold months.

The water budget estimates were included in the belief that they

would better characterize the moisture environment than precipitation

values alone. Calculations were based on the formula of Thornthwaite

(1948), an assumed soil moisture capacity of 14.0 cm., and the declining

soi 1 moisture avai 1abi 1i ty model of Thornthwai te and Mather (Baier,

1968; Chang, 1968). The calculation was continuous, from one year to

the next, yielding a continuous record of water balance conditions over

the period for which data were available. It was this calculation which

produced the water deficit estimates used in Section IV above. A1 though

the Thornthwai te formula is known to underestimate potential evapo-

transpiration in arid areas (Chang, 1968), the method is in common use

and may be employed when only temperature and precipitation values are

available. It was felt that the direction and relative magnitude of any past fluctuations would be reliable, even if the absolute values were

in error.

A1 though several climatic stations presently exist within the

study area, only the record for Keremeos is of a length comparable to

that of the establishment index series, and derives from a central

location within the array of sample sites. It is on the record from

this station that the above calculations and the subsequent analyses

are based. ,

C. The Structure of the Analysis

The analytic procedure used was that of stepwise multiple

correlati on-regressi on (Draper and Smi thy 1966), using the above climatic elements as independent variables, and the recruitment indices from Section I11 as dependent variables. The procedure provides a means of selecting from a large set of potential independent variables those which have high correlations with the dependent variable, and provides a solution which conforms to the mu1 tivariate and additive properties of the sieve model proposed by Harper and White (1970).

The strengths and weaknesses of the stepwise procedure have been discussed by Hauser (1974). Among the latter may be a failure to provide unique solutions, especially when the independent variables are not mutually independent, and a failure to identify those variables which are ecologically, rather than statistically important, due to coline- arity among the independent variables or non-1 inear response of the dependent variable. The problems induced by col ineari ty among the independent variables may be avoided by f irs t rendering the vari abl es truly independent by means of an ini ti a1 principal component analysis , but this approach, while technjcal iy elegant, serves only ta compound the problerr, of identifying those factors which i nfluetxe particular physiological or competitive processes. In an attempt to overcome this problem, the results have been presented as a set of primary variables-- those i ncl uded in the analysis by the s tepwi se sorti ng pro- cedure--and a set of secundary variables--those hhich at some stage of the analysis had partial correlations adequate for inclusion in the final modal, but which were rejected in favour of another variable due to col i neari ty. These secondzry varicb; es were then inspected to deter- mine, -if possible, the-i r relationship to primary variables chosen, and in one case were substituted iilto the analysis, in an attempt to arrive at an ecological ly more real istic sol uti on. This procedure appears to retain mlrch of the selective power of the stepwise solution, and-allows the r~sulf to reflect ecolcgical as wel? as purely statistical logic. In performing the regression-c~rrelatio~andlysfs, it was necessary to match tho drzpenrlent and indcpe!~dontvz..riat;les so that recruitment success in a given year was predicted by the climatic variables for an apprcpriat;e time period. it seemed probable that recruitment success during a particular year would be it?flucnced by weather conditions not only during th;:t yar but a;so &ring the previous year when the seed w~sproduced, and perhap during the following year when the seedling wa; stjll relatively mall and vulnerable. Accord- i ngl y , the i ndependefit mriabl es wer? smoothed wi th a three-year movi ng averac;e, so that the predictors Decme the mans of three consecutive years. A further pr~ble:ilarose froi.;; the p~ssibility of errors in the entire establishment series. In several tria.1 znalyses in which the independent variables were lagged against the dependent variable, maximum coefficients of determination were obtained when the establish- ment year was lagged one year behind the midpoint cf the three-year average predictor--i.c. when the establishment index was predicted by the mean of the climtic conditions of he cstzbl isbment year and the two years preceding, and thjs solution was adopted for analysis and interpretation. This result suggests that some consistent underaging of the sample stems has taken place.

D. Results and Discussion

The rzsults of the stepwise correlation analyses of the two establ ishmcnt. i ndi ces (one ~rsiPCJ the negat?ve exponen tiai mortal i ty correction Model 1 and the other the power fur:cf!otl correction Model 11) are shown in Tables IV.6 and IV.7. The tables show the primary variables included at each step in the analysis, with the cwfficient or" multiple 2 correlati~tt(R), the coefficient of determination (K ), the 'increase 3 in explanation' (ciRL) , the Beta value (6) , and the corresponding individual F rat'o. Appended are the secondary varf~bles. All of the primary variables are significant at the 1 percent level or better. In Model I, four el imatic mrisbles account for 53 percent of the variance of the estiblishment index--the variance remaining after extractSon of the temporal trend. In Model I1 nearly 70 percent of the uncorrected age class frequency pattern is explained, 32 percent by the age of the frequency classzs, and the remainder by three climatic variables. In this ciise, October ten!perature is .tirst included, and TABLE IV.6

Mu1 tiple Regression Resul ts: Age Structure (lksztive Exponent.ia1 Modal I) and Climatic Variables

Step No.- Variable -R --- R~ gy -- B i 1 December terop. .4797 .2302 .2302 .6750 34.42**

2 June temp, .5543 .3073 .0771 .5568 19.65** 3 Noveil~ber l;t?mp. .6525 .4258 .I285 -.4799 18.27**

4 July preci !I. .7305 .5336 .lo75 -3835 10.41** Constant -8.297

Final F Ratio = 12-87; D~greescf Freedom = 4/45; p less than .01. e. Secondarv Variables

Corre'i a ti on posi ti ve June przcip. pos i ti ve October D nsga tive .July AE positive

** Significant at the 1%level. TABLE IV.7

Multiple Regression Results: Age Structure (Power Function Model I I) and Cl inlatic Variables

A. --Primary ---- Variables --Step No. Variable I? 1 LOY]~P.Y~ .56,77

2 December temp. .6743

3 October tenlp. .720J 4 October precip. .7707 5 October mois turc deficit .6346

6 Gc toher temp. .8346 .6966 ,0000 removed Constant 4.927

Final F ratio = 25.8; Degrees of freedom = 4/45; p less than .01

B. ---.- SecondaryVar-i-- ab! es--

--Vari ah1 e.- -Correlation Apri 1 D pas iti ve May D positive April temp. positive October AE positive

** Significant at the 1% 1evei. then deieW from the model when th? addition of further variables decreases 7ts contribution to the variance e>iplair.ed below the level of significance.

In hth models, four secondary variables appear. In most cases these variables are closely related to those which actually appear in the models, ei thw by season, as i n the case of May and June temperatures in Model I, or fvnctiona lly, us in the ca;e of October AE and D in

Model I I. The s imi lai-i ty betwen the V,vo models is niore pronounced if both the prirnary and second~i-yv2riab:es are considered; October D appears as a secondary variable in Model 1 but as a primary variable in Model 11. Spring temperatures are repwseiited as a primary vari able in Model I (June temperature) but as s secondary variable in Model I1 (April temperature). Apri 1 and May moisture deficits, which appear as secondary variables in t%xiel*I: iTiaL1 be functional 11 relaxd to temperature, or have soine indcpeident ecolqi ml significance.

Table 1'1.8 shows an a1 ternate version of the results in Model 11 (Model IIa) in which an attempt has been made to test the significance of spring ternperature as a primary variable. Apri 1 temperature has been 'forced' into th? ara13sis as the first stzp, and is found to wake a significant contribution to the total variance explained, while causing slight ctiangcs i 11 the other varidbl es chosen. The total variance explained rises slightly, to just over 72 percent, and in this sense

Model IIa is an improvement 9i-1 the original Model 11. Clearly, many such al ternate models are possible, and the simp?e stepwise solution is nei they tlnique nor optimal, as Hauser (1974) nas expldi ned. However, it seems unlikely that any such alternate models would reveal a fundamentally different strticture from the three which have b2en presented. TABLE IV.8

Mui tiple Regression Results : Age Struct.ure (Power Functi on Model Iia) and Climatic Variables

Step NO. Va.rizblc -R - -dfi2 -e F 1 April temp. .0012 .0000 -0090 .21% 4.35**(Final)

2 Log. age .6015 '3615 .3618 --.4C56 1E.36**

3 Flecember temp. .ti873 .4724 .I106 .4632 25.41** 4 October tenip. .7457 -5560 .0836 -.3431 13.98** 5 October preci p. .8211 .6742 .I182 -1.0147 17.62"" 6 October zctua.! evapotranspi rztion .8498 .7222 .(I481 .7179 7.43** Constant 3.9318

Final F Ratio 18.6 Degrees of freedom, 6/43 p 4 ..ol **Significant at ihe 1%1 evei .

The analyses indicate that climatic control of reproductive succes; of ---Artemisia ------tridentat3 --- - in this area is considerable, accounting for 36 to 53 percent of the establ f shment index varjance, and mu1 ti- variate. The analyses probably underestimte the actual degree of climazSc control, far they do not include long-term climatic effects such as those suggested in Section IV, or any non-;incar relationships which may exist. The rer;ioval of temporal trend as a mortality correc- tian may also disguise some climatic effects, because any recent population increase due to sccular climatic variation would have heen removed with the temporal trend, prior to analysis. The averaging procedures used impose a iurtkr restriction. F:)r the three year average prezl udcs the possi bi 1i ty of accura tc rconthly val ucs. lhe choice of individual variables is assumed to reflect the control of physiol ~gica1 processes by cl imate. The posi ti ve correlations between the es tab1 isliment indices and December temperature imply 1ow temperature damage to seedlings. This inference is supported by the ohservati ons of winter seedl i ng damage i n experinient.al gardens by Marchand et a1 . (1955). The negative correlations with October and November temperatures may reflect a requirernent for a period of harden- ing before the onset of severe winter weather. The positive correlations with spring temperatures appear to confirm the findiqs of Harniss and

McDonough (1975) on temperature dependent growth rates i n Artemi si-a tridentata, hut argue against their conclusion that spring temperatures have no effxt on seed1 i ng survival under f i el d condi iions . Daubenmi re's (1975). observation of drought semi tivi ty in first year seed1 i ngs is supported by the positive corre1ations between the recruitment index of

Model ! and early summer precipitation and evaporation rates. The suite of fall moisture conditions shown as significant predictors include a negative correlation with October precipitation, but also a negative corrzldtion with October moisture deficit and a positive correlation with October AE. Arternisia tridentata- blooms in

October, and these corwlations may relate to the process of flower and seed production. A1 though adequate soi 1 moisture may be necessary for flower and seed production (see Figs. 4.13 and 4.lk), rain during this critical period may dam2ye flowers, or interfere with pol 1i nation, leading to reduced seed crops and lower recruitment success. Figs. 4.13 and 4.14 - -Artemisia- __ tridentata _ _ _ -___ at Site D. The roadside plants are in heavy bloom, while the plants behind shov little or none. This appears to be a response to the extra water which drains off the paved surface. F. Validation These models relate temporal climatic variation to temporal vari- ations in reproducl~vt? success in Arteinisia tridentata, If the models are valid, they should also provide some explanation of the spatial pat- tern of the spxi~s,For the species xi1 1 persist only where the mean recrui taent index exceeds some critical value. If the n~odelsare used as predictors of the recruitwnt index, using medr~ climatic data from suit- able stzti cns , the suatia'l pat ley cf reproductive success may be estimated. These calculated establisment i~dicesshc~uld ted to discriminate betweer: staticns wiihS 11 the presmt ransc of Artemisia tridentata (high index values) and those outside the present ratlge (low index values), and in general the index should tend to decline with increasing elevation.

figures 4.15, 4.16 and 4.17 show such calculated index values for

Models 1, 11, and IIa respective;y, plotted dq a 4uwt?or! of station ele- vation. Stations wt thir! the present range of Ar---eiiiisia tridi?rdata are indicated by closed circles, and those from outside the present range by open ci rcles . The abil i ty to discriminate between stations within and outside the present range, tind the degree of correlation with elevation have been used as measures of model performance. Under these criteria, Model I gives the best rest!lts, providirxj both clear discrimination and a high negative correlation with elevation. Model I1 is the worst, with geneim- a1 ly poor discriminating abi 1i ty , and a 1ower correlation coeff i cient. Model IIa is nearly as good as Model I, both in ability to discriminate and in the correlation achieved. It may be cocc!uded that in general the models do predict establishnient indices w!lich are reasonable in light of the present spatial distribution of -----Artmisia tridcntata in this area. Fig. 4.15 - Predicted recruitrnmt index values, Model I, as a Function of elevation. Closed circles are stations at which -Arteml's-- ia- trider,r,ata is present; open circles are those at which tile s:.vzies is rare or absent. Stations are: (1) ticdl?:~, (2) Kelowna, (3) Keremeos, (4) McCulloch, (5) Okanctqan Ccntre, (G) Oliver, (7) Osoyoos , (8) Penti c tzn , (2) Vernon, (10) Merri tt , (11) Joe Rich Creek, (12) Princeton. --- - I 10 ZG 3000 feet 4000 Elevation

Fig. 4.15 - Predicted recrui tmen t index val ms, Model I I, as a function of elevatio~. Station nu~5ersare the same as those of Figure 4.15, Elevation

Fig. 4.17 - Predicted recruitment index values, Mode! IIa, as a function of elevation. Station numbers are the same as those of Figure 4.15. G . -- Smnaty Correlation analysis of the establishment indices derived from the regianal age structure of Artemisia tridentata-- indicates tha:: a substantial porti~nof the year-to-year variation -i tl reproductive success may be attributed to climatic co~trol. High establishment rates arc correlated with relatively low fall arid high winter :imper;tures, high spring temperatures, 1imi trd sunmer drought, and low rai nfa'l l and high sail moisture reserves duri ny the fa7 7 f loweri ny period. The cornbi nation of these controls appears to provide some explanation cf the present spatial pattern of the species in this area. If the prssent range, and recent fluctuations in derlsi ty within that range can be explained it: terms of climatic variation, it is possible that changes -in ranye or density in the nore distant past nay have had similar C~LIVS, but the cmqlex nature of the cl ivratic centrals on this species must aake any sinnple cl imat-ic i n~erpretationof paleopopulatiorl azta u!lccrts l n,

!!I. ----The Effects - of Intra-specif ic Co~n~r'iition

The purpose of this section is to explore the possibility that i ntra-specifUic i nteractiofis betwen mature and seed?i ng Artemi sia tridentata inf1 uence the temporal or spatial pattwns of recrlii tnlent within stands. Because space and resciurces within the stand are finite, there must be some upper 1imi t to stand density, beyortd which suppres- sion of new recruitwent, c)r increased mortal Sty of adult plants wi 11 occur. Fowever, dw to otkr form of pop~ilationcontrol, actual stocking levels may seldoni or never reach th~seat, which intra-specific i nteractions become inpor tant . Suppression of offspring by parent, or of one seedling by another, may occur through competition for space or other resources, I through infection by pathogens or herbivores (Janzen, 1970; Connell ,

l97l), or through allelopathic inhibition (Rice, 1974). The action of such mechanisms wi thi n stands may contribute to the irregular population

age structure described in Section 111, if successful establ ishment in one period leads to decreased establishment in a subsequent period.

A. Evidence of Intra-speci fic Competition in the Age Structure Sample A demonstration of density dependence requires that recruitment at time period A plus 1 be a negative function of the density at time A, at least for high density situations. In order to test for density dependence in the Artemisia tridentata population the quadrat data from the age structure sample were examined for the existence of such a relationship. The test was performed by regressing the density of plants less than ten years old on the density of plants greater than ten years. The set of all quadrats was divided into groups on the basis of the density of plants greater than ten years old. The limits of the groups were determined arbitrarily so that the quadrats were distributed relatively evenly among the groups so defined. Thus, the subdivision at the low end of the density scale, where many of the quadrats fell, was in units of 0.25 plants per square metre; 0 to 0.24, .25 to .49, and so on, while at higher densities larger groups were used, the last combining all quadrats with densities greater tham 4.0 plants per square metre. The 1arges t group contai ned seventeen quadrats, and the small es t one five.. Within each of these groups the mean density ~f plants undsr ten years old was computed. This grouping procedure imparts to the data a

statistical stabjli ty which is absent if individual qdddrat values are

used, and avoids the problems caused by many zero values. The density dependence hypothesis imp1 ies that there shou! d be hish dasiti es of young plants in low densitv groups, a~dlow densitfes iri high density groups. Because of the irregular group size, Spearman ' s coefficient of rank correlation (Siegel, i955) was ure3 as the test statistic. The results are shown in Figure 4.18. Establishment densities do not appear to decline systematically in response tc increased densi- ties of mature plants. A similar test (Fig. 4.19) was performed using the frequency of plants under ten years old as the dependent variable. Again, there is no systelnatic decl it?€ with increas; ng de:lsity It m3y be concluded that, at least at the densities commonly encountered in the f-ield area,

the density of ~ldplants has little effect on t-ecrui twrlt success in

Artemi sia tridentata.

It was suspected that these results might have been biased by

the pooling into single density classes cF plants of rsany differen-t ages

and sizes. Accordir,~ly,a further test was devised in which the estab-

1ished populat-ion wds represented by a density index which combi ned both simple density ana plant age as a surrogate for size. This index, 'sage years per square ~etre'was calculated as the sum of the ages of all plants over teo years old in c3ch quadrat, divided by the quadrat area. The set of quadrats was a~ainstratified irtto groups on the basis

of this index, and recmi tmen t f!-e7:iency cal cu! a ted for each group. Density 2 plants (10 yrs

1

0

0 0 1 2 3 4

.$ .7 Frequency .6 plants t10 yrs e5

.4

.2

Fig. 4.13 (above) and 4.19 (hc?ow). Test for density dependent re~riiiWent i I: .Art& -. --. . - - - -. sit1-. --tr.identaii;a. -- - Density and frcr;:r?ncy of planc~less tkin ?;en years old, as a function of the dws.I ty of olc!er plants. Neither correlation ::oeFf icient is si2r!i f icant, Again, it was expected that recruitment frequency wxld decline with increasing density index values. The results are shown in Figure 4.20. Tkre is a significant negative correlation between recruitment frequency and this index of pre- recrd?tmnt dens i ty . If a composite irdex of density and agz appears to affect recruitment success while si~p'iedensity does not, it may be hypothe- sized that the observed relationship is due to the effect of plant age alone. In order to test this hypothesis the set of quadrat data was stratified into groups defined by t$e presence of plants of a particular age. Thus, the first group consisted of a I1 qbadrats containing plants betweec ten and fourteen years oid, the second of quadrats with plants between fifteen and nineteeri years, and so on, R.xruitzent frequency was again calculated in each group, a procss equivalent to calculating the probabi 1ity of finding a plant less than ten years ole in a random quadrat also containing one or more plants of a particular age group. It was hypothesized that recruitment frequency would decline in the presence of older individuals of the same species, as a function of the age of those i ndi vidual s . The results are shown in Figure 4.21. There is a highly signi- ficant r,eqdt-!ve re1 ?tionshi p between recruitment frequency and the presence in the quadrar of older individuals. it may be concluded that it is the age, rather thar: the density of the establ-isbed population, which is the principal fzctor in popl-ilation self regulation in

Arternisia tride~tsta.- Fig. 4.20 - Test for density dependent recruitment .in --Artemisia -----tridcntat3. Frsquency of p?h~tsless tlxn tt:: years GI~as a function of age-derls-ity i:~d$xaf older plants. Correlation significant at the 1%Icvel . ln S- v- a r- -u -C? r-. 5 C) i-\ ln + LL! 0 Nhat is the mechan~smwhich produces this effect? it is appar- ently not competition for resources, for this should be reflected as density rather. than age dependence, and there is 1 ittle evidence that the effect declines or levels off for plants older than fifteen or twenty years when full size is normally achieved. Seed prctiuction may decline wit.h age, but all of the sites sanlpled had iarge and well disper- sed popirlations of yomger plants in the ten to twenty year age group, and seed availability does not seem tc be a probable cause. Attenipts to correlate thc presence of y0ur.g plhnts with the preserrse 3f plants of the ten to twenty year age class ie a two by two contingency table yielded insignificant results. It is uclikely that the effect is due to infectim of the young plants from the old, for the probability of infection seem unlikely to Sc related to the age of the ccrrier. Some form of allelopzthic interaction appeared more likely. The inhibition of geraination in seeds of test species by water soluble toxins in the leaves and litter of Artemisia tridentata has been reported (Ried, 1964; Schlatterer and Tisdale, 1970), but the test species used appdrently did not include --Artemisia tridentata itself.

Because the tox l c ~gentsare water sol ubl e , under ser,ij -arid condi tions they may accuminuiate in the soil over time, and so acCoili71r; for the age dependecce obcers:led. The fo! lcw'n? section cfescrihes an experiment designed to test for evidence of auto-allelopa~hy in Artemisia tri denta ta .

0. A Test fcr A~1b-al1e1op~tky

A1 'lelopathic effects my be investigate4 by watering the seeds of one or nmre test species wjth an infusion of the leaves or litter of the species rmdw study, but this procedure n~akes .it df fi'f cu1.t to match toxin concentrations with those which rnay be present in the field and does not allow for possible destruction of the toxin by soil ~icro- organisms. Ir, order to avoid these prcblens, an experiment was conducted in which gerrr;ir:zt-i:onand survival of -Artemisi'a -tridentata -- on a control substrc?tii was cornpzrcd to values obtained from seeds sown or; a substrate of surface soil collected under large old -Artemisia tridentata-- at Site J.

The experiment was conducted in "Le same manner as that described earlier for the effects of bare ntnerai soil sites, and the bare soil treatment in that experiment was used as the control population in this one. Some unsown replicates of the 'sage soil' treatment were retained as a check on residual seed. The results are shown in Tables IV.9 and IV.10. Germination was defined as radicle emergence, and germjnation rates in the 'sage soi 1 ' treatwent were found to be relatively high, ranging from 88 to 109 percent, only slightly lower than those observed ill the control pots.

However, seedling development on the sage s~iisubstrate was poor. In many cases, the radicle became blackened and withered, and failed to penetrate the soi 1. Many failed to expand their cctylecons, and ul ti- mately died. The pots were waterea fr~mb~iow, and it was observed that a black tarry substznce, apparently derived froin the sagebrush 1i tter, accummula ~edat the soi 1 slirface in the experimental treatment.

At the end of 56 days 1 ivi ng plants in the 'sage sojl' treatment amounted to 56 percent of the seed input, as against 95 perreat for the control. This Figure includes seme extra seeds beyond the 25 sown in each pot, which were apparently residi~alfrom a seed crop of a previous year. TABLE TV.9

Germination of Artemisia------. --tridenti..ts - .. -- -- .. . - - or; Surface Soi 1 Froin Under -.ArtemS .- -.- si -- a --tri -. den-ata------Canopy

Sage Soi 1 Treatment Coritrol Rep1 i ca te ----- # % -- ff- -- - -'!

n .. 1 2 2 88 LS 180 2 25/26 9 6 25 100 3 24 9 6 2.5 100 4 25 10C 25 100 5 2 4 96 25 100

TABLE IV.10

Seedl -ing Survival in --Artemisia -trfdwt8 -- - -- ta - - on Surface Soil From Under Artemisia- tridentata Ca~opy

Sage- Soil Treatment Control Rep1 i ca te Number A1 i ve Number Al i ve # % ----- # X 113

These are marked in Tables IV.9 and IV.10 as germ i nation and s~rvivzl rates out of' 26.

C, Discussion It may be concluded that there fs evidence cf allelopathic suppression of recruitment in -Artcmisia tr-i dcntata s tards by the mature plants, and that this suppression is probab1.y responsible for the observed patterns of aye dependency, This 1n2chanisrn may be expected to affect the spatial distributior, 9-f seedl in95 within stands, for the probability of seedling survival should tend to i~creasewith the dis- tance from nature plants. The degree to which this mechanism may be respons.ible for the modal , non-reproducti've age s truc ture pattt2rns observed in m3r1y

Artemisia- .----trider~tatd stands is !wre uncertai n. It might be expected that successful establishment in we period nould tend to reduce the chances of establishment in a subsequent period through allelopathic interference. Such an effect may be present for a time aftcr the crea- tion of an even aged stand by invasion or succession, but continued adult mortality and replacement as th2 stand ages should ten3 to result in a wider spread ii? age classes over timc., ait!~o~.ghallc;f~pai,hic sup- pression n:ay still be important at a local scaie. Ry itself, then, allelopathic suppressjon is probably incapable of maintaining strongly modal age distributions over more than part of a generation in time, or over any great extent in space. however, it may be able to accerltuate a modal age structure which derives init-iaily from some other cause, such as a periodic establishment 'window' coqtrol led by climate, or periodic destruction of the population by firc . VII. The Effects of Fire

The existing 1i terature on Artemisia tridentata (Chapter 111) indicates that fire is capable of destroying stands of this species, and that successional replacement of these stands commonly requires periods of fifteen to thirty years. Consequently, periodic burning may be capable of suppressing the population over wide areas and for extended periods. This long-term effect is treated in Chapters V and VI.

Artemisia tripartita and Artemisia frigida are reputed to be more fire tolerant (Hi tchcock et a1 . , 1955) and may stump sprout after burning. Periodic burning may therefore provide these species with a competitive advantage relative to Artemisia tridentata, and thus promote a relative increase in the abundance of these species over that which exists in the unburned stands at the present time. Historical data in support of this hypothesis are presented in the following chapters.

The purpose here is to investigate the relative changes in species density which occur when modern stands of Artemisia tridentata are burned. The hypothesis tested was that fire in this environment leads to an increase in the abundance of Artemisia tripartita and Artemisia - frigida relative to Artemisia tridentata.

A. Method

Data with which to test this hypothesis come from the site of a recent burn near Richter Mountain, Site M (Fig. 4.1). Part of the area had been burned five years before, and the edge of the burned area was easily recognized as a sharply defined line on the landscape (Fig. 4.221. The site was the oldest of four recent burns known in the study Fig. 4.22 - Burnt sample Site M at Richter Mountain. -.Artemisia .-tridentata -.- -- has been removed from the clear area in the distance by fire. area, and the only one in which successional pattcrtir were evimnt. The area had.been grazed, and grass cover was lovi at the tix the saniple was taken in the fa1 1 of 1975. The area was sampled by two line transects laici at app:f~..c-imtely

right angles to the burned-unburned boundary. The sample consisted of 76 two by two metre quadrats, 50 in the burned area, and 26 in the unburned area, spaced in pairs at five metre intervals along tk tran- sects as shown in Figure 4.23. The numbers of old ?,i-temisia --.-trl;dentata,

young (less than four years) ---Artevisia trfden tats,- -Artemisia--a- --Wparti ta, and ----Artemisia -frigida - in each quadrat were recorded.

B. Results md Discussion- The results are sham in Table IV.11. A few old Arten-;-isia triderrtata individuals remairl in the burned areq, tcl the chs

-Artemisia - -- - - tri- parti --- ta densities have a1 so redijced subs tanti- ally, indiciiting that this species mdy be less fire tolerant than previously reported. There is 1i ttle difference in apparent Artemisia frigida density, but the sample size for this species was very small. A1 though -Arterni sia tri parti ta densities have been reduced by burni ny , only a relative difference in mortality is necessagy to produce a shift in species dominance under a regime of repeated fire. A test for difference in relative mortaii t.y was conducted by coxparing the nwnbers

TABLE IV.ll

Shrub Densities on Burned and Unburr,cd Areas, Richter Mountain

2 Standard Densi ty/m (4) -- Deviation' -- -- - 01 d Artcm-isia- trjpartata Burned Unburned

Young Artemi si a tri partata Burned Unb~lrned

--A-Artemisia tripartita Burned Unburned

Artemisia frigida Burned Unburned

* = ~~0.01 ** = p 5 0.05 N.S. = not significant i 119 t

of Artemisia tridentata with the numbers of Artemisia tripartita and Artemisia frigida, on the burned and unburned areas using a Chi square contingency table (Table IV.12). The proportions of the two groups were found to be significantly different on the burned and unburned areas, with Artemisia tridentata dominating the unburned stand, and the other

species relatively more abundant on the burned area. It.may be conc uded that fire in this environment tends to shift dominance of the shrub community away from Artemisia tridentata toward Artemisia tripartita and Artemisia frigida. It is likely that these data underestimate the extent of this dominance shift, at least at this site. The burned area contained several large clumps of Artemisia tripartita which did not fall within the planned sample array. A further sample from one such clump indi- cated Artemisia tripartita densities of 5.7 plants per four square metres, and Artemisia frigida densities of 0.87. These clumps contained many burned Artemisia tridentata stumps , at densities comparable to the rest of the burned area, and are believed to represent post-fire expansion from a few individuals. No such clumps were observed in the unburned area, or at any other low elevation sites in the study area. The relative rarity of Artemisia tripartita and Artemisia frigida at low elevation sites at the present time may limit their ability to achieve dominance after removal of Artemisia tridentata by fire. If fire were to become more frequent, the effect of this dominance shift would probably increase, for subsequent fires would burn areas with lower Artemisia tridentata, and higher Artemisia triparti ta and

G Artemisia frigida populations than generally exist today, and succes- i L sion on such areas would tend to reflect these differences in seed TASLF IV.12 - Tcst of diffei-ential fire semf tivitj in

-Artemi-- sia -tricientata -- - and other hrte~isi a- species. ?he other species are -A. frigida and -A, -tripartita. Cell frequencies are total pla~tsin burned and unburned samples. Figs. 4.24 and 4.25 - (above) Ssrnple SIte H in the summer of 1974. (belcw) Site H after f ire in 1975. The skeletons of the --- Artemisia trldentata- remain, but are not resprouti ng . Figs. 4.26 and 4.27 - Arteai si-a tri parti- ta (a bow) and Chrysothamnus- ---nauseosus (below), resprouting after fire at Site H. Fig. 4.28 - --Artemisia -_tripartita resprouted and in bloom four years after fire at Site M. The shru?s in the ~liiddiedista~t left are Artenii'sia tridentata. - -- -.-. --- .-- availability. It may be hypothesized that the ncrmal succession in this area is from --Arterni si a tri parti ta and tlrtttniisia -frigida -- to .---Artenli sfa - tridentata, provided that initial seed sources are available. In addi- tion to initiating this succession, fire may serve to maintain the shrub community at a particular successional stage, depending cn fire fre- quency; an Artemisia tridentata dominated cummuni ty under low Fire frequency conditions , communi tias i ncreasi ngly domi as tsd by Artemi sia tri parti ia and Artemi s ia Tricjida. as f i !.e frequency i ~creases,and communities from which both --Artemis.ia - tridentata- -- 2nd ktgmisia triparti ta are largely absent at high fire frcquencfes. Data with which to test these inferences are not available on the present landscape, and further evidence on the role of fire must cow frcn the historical record.

VIII. -Sunmar-y--

Exafi.ination of the present Artevis ia tridentata population permits some assessment of the factors which control the range and density ~f this species at the present time, and which may have deter- mined any changes in range or density which occurred in the past. Climatic fluctuations appear to play an iwportant part in determi ni ng recruitment success, influencing bcth the range and the age structure of the population. Climatic influence may be direct, as when seedlings succumb to low spring temperatures, summer drought, or low winter temp- eratures, or indirect, as in the proposed linkage between prolonged drought, bare soi 1 n?i crosi to avai 1abi 1i ty, dcd seed1 i nq survival . Past population changes may therefore ref 1ect cl irnati c chafige , a 1 though the complexity of the cl iniatic coni;racis will mkc interpretation of such nopulation changes di fficul t. It has becn demonstrated wder 1aborzt.cy'y conditions that

seedling survival is related to the availability of suitibla bare soil microsi tes. The avaiiability of such microsites in the field may be determined by c'l iniatic condi t-ions or animal ai sturbance, ar!d a7 though grazing disturba~ccdoes n~tseem to have becn an fn~pc~rta~tinfluence on estdbl ishn:ent success in the recent past, 'it may have been so at other times. Grazing disturbance is not a prerequisite of successful

recruitment for this specis in the areas exzmined, but such disturbance may serve to increase the temporal fr~qcencyof successful recruitment, or the density of recruitment ciuring such periods. Zn areas where the natural frequency of bare soil microsi tes is insufficient to maintain a viable population of Artemisia tridentata,- the introduction of doxes tic 1 ivestock my have provided the necessary condi tions for invasion. The proportion of t!?e present range which consists of such 'sensitive' areas .s unknown, but is apparently t:ot large. Such areas may be concentrated near the upper altitudinal limit of the present range, where the natural frequency of drought conditions is lower, and grazing disturbance in such areas may be of greater inlportance in the establ ishxent and maintenance of the population.

The effects of intra-specific competi ticn are detectable in the stands studied, and appea:. to be due to sorne forn of allelopathic suppression of seed1 i ngs by the established population. This inter- action may be responsible for the absence of discernible grazing effects over the past ten gears, or for other fzatures of the age structure of the present population, but is probably incapable of exerting a signi- fjcant influence on the long-ter~dynamic: of the gopul ation. Such a mechanism cannot account for the absence of the species at particular times and places, nor for the subsequent invasion of such areas. Fire is not now a major element in the population dyr:antics of

Artemisia------tridentata in this area, but may have been SG in the past.

The 1imi ted e8~idenczavai lab1 e from the present 1 andscape suggests that recurrent fire would lead to much lower equilibrium populations of this species, and perhaps to rep1 acement wi th other, fire to1 erant species of the genus. 'The impact of fire should depend, in part, on the time necessary for reinvasion. Reimasi'or; rates after such events may be slower at high elevations due to the lo~lerfrequency of favourable climatic conditions, and the impact of fire may be relatively greater in such areas than in the valley bcttoms.

Cl imati c f 1uctuati ons , grazi ng di s turbance and fire a7 1 appear to be potentially capable of influencing the dyna~ic~qgi libriurn which determined Artergisia ------trid~ntata abundance in this area. It remains for the historical record, to which the following chapters are devoted, to indicate which of these factors have actirally beet) important in the past, and which have not. If the inference that grazing disturbance is not a prereq2ssitz to successful reproduction in this area is correct, it might be expected that the introduction of cattle after 1860 would have little effect on zqsi iibrim krte~13ia t.r-i$ai~tata population size, except perhaps near the range margin, If past fire frequencies can be determined, it may be possible to examine directly the effect of differ- ent fire regimes 91; the size and composition of the Artemisia-- populatio~. In more general term, pal eo-populati on data may answer the central questicn of the role of Artemisia-- tridenka& sn the grasslands of this area prior to, and imediately fo1 lowing Eurapean settlement. CHAPTER V

DOCIJMENl'ARY RECORDS

I. Introduction-

This chapter attempts to draw together a body of documentary evidence related to the Artemisia- trider~tats,population of the study area during the early settlement period, rol~ghly1659 to 1920. Prior to this period, documentary sources are absent and inferences about vegetation type and vegetation change must be made on the basis of the fossil record, ~hichwill be treated in Chapter VI. The material to be treated here consists of the cou~mentsof early travelers, batanical records, and early photographs which deal with the distribution and abundance of Artertiisia tridentata, and with the frequewy zcd Snpact of fire, in an era before effective fire control was introduced. The use of documentary records to determine vegetation change and environmental history entails several problems. The qua1 i ty of written records is variable, and depends cc the care with which the observations were made, the time spent ir, the area of interest, and the proportion of the area observed, as well as the training and biases of the individual observers. Observations in the area by trained botanists or other scientists are of particular value; many early observers of the landscape ;n the study area were not scientifically trained, and their observations are of correspondingly less valde. This lack of botanical expertise is particularly widest in the often conf~lsirlguse of common names, or abbreviated scientific names of species, making prcci se tax~nomicinterpretaticn difficult. In the following extracts the terms 'abs i nthe' , 'wormwood' , 'artemi sia' , and

'sage' cr 'sagebrush' are all used for --. Artemisia spp. In some cases, it is clear from the context that 'worm,vood' was used as a synonym foi.

Artemisia frigida,-- but this usage does not seem to ba universal. 'Sage' and perhaps 'artemisia' were apparently used for shrubby species of the genus, but whether for Artemisia tridentata or Aiitemisi;r tri parti ta is seldom made clear. Artemisia --trifida Nutt., employed by Macoun (1883) and Dawson (1878) is an early synonym for ----Arternisia --triparti t3. Even when the observer was particularly careful, the record may reflect only a very limited sample in time 3nd space, and quite mis- leading impressions mcy result. Some statistical control cn this problem would be provided by a relatively large n!.mbe)* of observers, but the data for such an approach are o ften lacking. In the discussion which foll ows , an attempt has been made to increase the number of observations by employing data from a w ider area than that of the actual field area, hut this entails the risk of i ncl udi ng observatio~s which are not repineserltative of the area under stiidy, and points for which this may be brae wi I? he noted. In spite of the limitations of available data, or perhaps because of them, the early settlement period may be considered the most important of the time periods under study. It is the perid .in which the veyeta- tion of the region was first subject to a sci te of new influences, including overgvazi ng , the introduction of new species, and perhaps, to fire. It is therefore the period when change, of the regional vegetation in general, and of the Artemisia tridentata population in particular might be expected to have been the most rapid and dramatic.

The early settlement period is of interest for another, and perhaps more important reason. The observations of this period have provided the traditional datum against which all subsequent observations of vegetation change have been judged. Effectively, the natural vege- tation of this area has been defined in terms of the conditions which existed in the period closely followi ng the first European settlement, a period from about 1860 to about 1880 or 1900, if only because this period is the earliest, and therefore, theoretically the most 'natural ' , for which direct observations are available. Whereas more recent vege- tation change may be observed directly, it is often difficult to adduce evidence of vegetation change in the period just before or during the early settlement phase, and it is often assumed, in the absence of such evidence, that the earliest observations record a natural vegetation in stable equi libri um with its physical environment. This assumption is based upon uniformi tarian princi pl es , but it is a uniformi tariani sm of state, rather than process, and must be treated with caution. The

'virgin forests' of eastern North America are now known to have been extensively modi fied by native agricul ture and burning prior to European settlement (Day, 1953; Heidenreich, 1971).

This problem may be exacerbated by the paucity of the data themselves. The earliest records are inevitably scattered and frag- mentary, and it is frequently necessary to employ material which documents conditions as they were after one or more decades of 130 settlement; conditions which may already have been a1 tered by fire or other interference. Vale (1975) in a documentary study of the pre- settlement vegetation of the Great Basin area, has pointed ON that there are important differences between the zccounts of the earliest travelers and those who came later. Much of the matcrtal to be pre- sented here may suffer from this pro~lem. One of the functions of the data to be presented in Chapter VI is that of an independent check on this a.spect of the documentary record. Three features of the histwical record are of interest. They are: (1) the location and abundance of Fwtemisia tridcntata and other species of the genus in the study area; (2) contemporary views of the timing and effects of overgrazing; and (3) the frequency and effects of fire. The first two of these will be treated together.

11. Documentary Materials: Gveryrzziry and the Artemi si a Popul atwn

The earliest acccunts come, not from the field area which was rather out of the way for early travelers, but from the banks of the Columbia River, 110 k,ilowters south of Osoyoos, at. the roui:h of the

Okanagan River. Sir Gecrge Simpson journeyed down the Columbia in

1824, ar,d wrote 3f the ar2a ar-ounJ Fort Oka~agar;:(Fig. 5.1)

The country vow becomes dreary and wretchedly sterile, scarcely a shrub to be seen, and here and there a solitary red pine . . . . Since leaving Okanagan there is scarcely a tree or shrub to be seen, and Fire Wood is so scarce that the Brigades passing frequently burn the pal 1 isades that surround the graves of the Natives (Spencer and Pol lard, 1937, Chapter 5).

Simpson journey,?d this way again in 1841: ii 42' ______--- 6 OQ G &! 1 Ii(;h';yi?

122' 118* gp. I I Figure 5.1. The ~acijkNorthwest. The banks of the Columbia as far as the eye co:~iri reach were dull and ntonotonous, consisting of a successicn of sandy flats with very scant herbage, and still less wo~d . . . tit? ;car- city of bush was so great that both yesterday ar~dtocia,!/ WE had to search along two or three miles for fuel; and sf'csr a17 we had to make our fire of driftwood.

Further south, where the Snake River joix the Col uwbia, the aspect was rather different: A more disnzl situation than that of this post (WaIlawa71a) can hardly t~cimgined. The fort is surrounded by a sandy desert which produces nothing but wormwood, exxpti ng that the horses and cattle find a little pasturage in the hills (Spencer and Poliard, jbid.) The important feature of these passages is the absence of

Artemisia-- tridentata, or any other woody shrubs, from the Fort Okanagan area where the soecies is now conimon. The 'wormwood' in the last passage

is probably not ----Arter~isia -fr'gida, which is readily grazed by cattle, but rather one of the shrubby species. The type specimen c~fArtemisia

tridentata was collected on the plains of the Columbia River by Nuttall in 1841 (Beetle, 1900), and it is likely that 'worn1;iood' in the above passage refers ta this species. The earliest recorded observations within the field area were made in the suxmer of 1253 or 1860 by a tr~ernber,of the bound:~ry survey party. A Mr. Custer crossed fron the Skagit Valley and descended the

Simi l kameen tct the imerbican bcrder . 3f the vai 1cy h: wrote: The soil generally throughout the lower valley is impreg- nated with it (alkali). TI72 basin is nearly destitute of timber, and of but little value except for grazing. A few patches of w2t and rich bottoq occur, but for the rest it is a71 sandy; and the presence of the srtemisis and the cactus alone would be sufficient proof of its worthlessness . . . . The mountains are sparsely tfmbered, and, where not denuded of soil , are covered i n fine bunch grass, as arc also the terraces and much of the bottont (G;bbs, 1874, p. 361). The Royal Engir~eercwere working in the area as ~~11in 1859: The grass is gewraliy of good quality, the prickly pe3r and ground cactus-- the sore enemy of the moccassi ned tv?vc?1 er-- being the surest ificlica'i-ion of an approach ti, ar! inferior quality. Tiniber is for the most part scarce, but coppices appear at the sharp bends of the river, tolerabiy well wooded, and abounding in an underbrush of willow and cherry (MacFie, 1855, p. 289). There is a reference here to grass nine feet high, along a stream. This may be the source of a similar reference by Mikkelsen

(1950, p. 1221, but it is evidently not typical of the area as she imp1 ies . The impression convey~dby these passages is one of open grass- land, not uniformly verdant, but certainly not dominated, as much of the area is today, by dense stands of sagebrush. Some species of --Artemisia was apparently present, and was cited as evidence of poor quality land, but the specific identity is unknown. The river bend coppices are still present, but the a.pparent absence of other timber is in contrast with the aspect of the present floodplain which, where uircultivated, is often covered with dense stands of --Popuius balsamirera. Similar accounts are available from the Lillooet and Nicola areas for th-is pericd (Fig. 5.1). Begbie (1861) wcte of a trip from

Lytton to iiliooet in 1859, that the country contained zhundant bunch- grass, and that the benches were ". . . 211 perfectly free from under- wood." Mayne (1859) mkes similar conirnents about the Thompson-Nicola area during the same period. MacFie (1865) was through the area a few years la tzr, and recorded a mther different impression. Of Li 11 ooet he wrote: "There are a few pat.ches of arable land, but sand seems to prevail. A71 along froin Douglas t.he country looks barren; hardly a 134 blade of grass to be seen, or a spot level enough to pitch a tent on." Again, he noted, ". . . Beautiful tracts of table land, thinly timbered, but parched and sandy, with very 1i ttle vegetation." Again, we find that references to sagebrush, which now form a prominent visual element of the landscapes in question, are notably absent from these passages, implying at least that its abundance was comparatively low at the time. The differences between the two sets of observations, in 1859 and 1863, may reflect the effects of grazing by cattle and pack animals near Lillooet, which had become, by 1863, a major node on the route to the Cariboo gold fields. The decade of the 1870's saw an increase in exploration and survey work in southern British Columbia. One of the first relevant publications in this period was a settler's guide and prospectus com- piled by the provincial Agent Genera1,G. M. Sproat, and published in 1873. By this time the dangers of overgrazing were apparent, for the book contains a lengthy discussion of the value of bunchgrass as stock feed, and warns that it is readily damaged by heavy grazing and tramp- 1ing (pp. 57-58). He comments, however, that "If bunch grass is destroyed, wild sage and absinthe usually appear; these are good cattle - food, especially for winter. Sheep are very fond of Black sage." The description of the Sirnilkameen Valley is very similar to those cited above, and may have been taken directly from them. Of the Nicola Val 1ey he writes: "First part of river unattractive; wild sage bushes; hot sand in summer . . . . River winds through masses of alder and willow." These early comments on overgrazing are applied to no specified location, and probably reflect rather 1ocal i zed observations . They should not be taken to imply that overgrazing and Artemisia invasion was general in the area by 1873. The 'black sage' of this passage may refer to Artemisia- tridentata.-- Beetle (1960) notes that 'black sage- brush' was a frequent common name for ktemisia tridentata in the early taxonomic l itera ture . Marcus Smith was in the Okanayan-Similkaneen area in 1874 as part of the Canadian Pacific Railway survey. He reported fine grazing land and luxuriant bunchgrxss around Keremeos, at Richter Pass, and in the Okanagan Valley south of Okanagan Lake. There is no ent ti on of either sage or overgrazing, despite the fact that Mr. Hayes, at Osoyoos, is noted as having 1,000 horses and 2,000 head of cattle (Flernming,

1877, p. 116).

Joht-~f4dcouh was in British Columbia in 1875, again as part of the rai lway survey. A1 though he did not visit the Okanagan-Simi 1kameen, his observa ti ous of the Fraser-Thompson area are particularly val uabl e, as they represent the earliest treatment of the lower grassland by a trained botanist. As he travelled north past Jackass Mountain, in the Fraser Canyon, he wrote: "Now all is changed, the sage bush, Artemisia

---.--tridentata becmles frequent, and at Lytton a group of Nevadz plants is the characteristic flora." Further up the valley h~ notes that the hills are clothed in hunchgrass, 'I. . . whi le ttie benches near the river are altogether bare, except for a few bunches of grass and the

-.-.-Artemisia -friqida which on all the interior plains throughout the United States and Bri tish Colmbia replaces 'bunch grass' when it has been eaten down. " "The extre~iebareness of the lower benches near the uwd arises,

I believe, from the fact of the grass having been coixpleteiy killed out by trave?1 i ng stock ." He speaks of ". . . . naked and arid bencks along the Thompson," I and, of the country between Soda Creek and Quesnel, an area beyond the I present range of -.---Artemisia ----tridentata, he notes that I . . . bunch grass . . . and the pasture sage brush, Artetrici-& -frigida, -- Here the leading plants. The latt~ris a gt-cat food plant of the cattle in winter, throughout upper 3r.i tish Columbia, Nevada, Utah, Wyomfng, and in facc s:l tw dry ! Northwest. It is said by the stockmen io be prcfcrabl? to ! any kind of grass or hay, and to have a wonderful effect on stock, keeping them fat and .leek in tk depth of winter (Macoun, 1875, pp. 110-232). A similar impression was recorcied by St. John, who accclmpa.nied the Dufferin tcur of 1876. Of the Ashcroft area hz wrote:

The hills forin benches or small table lands at varying heights and of varying dimensio~salong the side of the road, and, of course, beyand the limits of our view. Thcse hills were covered with wormwood, and here and there a little sage. A large part of the district is covered with bunch grass, a very nutri tiow kind of feed, but in the f m~ediate neighbourhood of the road we did not see any. Where the bunch grass has been eater: down, repeatedly ws.rin!:lcod springs up and answers the purpose of the plant it has displaced [St. John, 1877, p. 143).

George M. Dawson was in sout.hern British Co;mbia in the summer of 1877. He noted that much of the bunch grass in the lower Thompson

Val ley had been destroyed by overgrazi ny , and went on to say: Bunch grass and thz small sage, Artemisia frigida, are the characteristic plsnts of this and other similarly situated dry valleys of the interior. Both of these plants are valuable as food for cattle and horses, but here, as in many other locaii tics, the former has Se2n almost entirely destroyed in the lower parts of the valiey by the careless herding of the large bands of cattle now owned in the country. The broken and declining edses of the plateaux on a15 sides still maintain, however, a Tuxu:"at gro$~th of bunch grass {Dawson, 1878, pp. 11-16). Moving down the Simil kameer~, he conanenti.cl on the pine and bunchgrass vegetation around Princeton, and, passing the wuth of the Ashnola River, wrote:

The rainfall is evidently iess, and the winter climate not so severe in the lower part of the valley. Saline encrust- ations beain to apcear on the soil and in addition to 9. . . . the cactu; and Arternisia friqida, Artenisia trifida occurs, forming a bush oTSGGTi(p,15~- --

Of the t owe~Ckanagan Val ley he rioted: Scarcely any trees are to be found in the valley bottom, or on its lower slopes. It is scantily clothed viith bunchgrass, now much reduced ow-ing tu the nu~;;St?rof cattle; and hxe zlnd there are thickets of ragged looking 'Chaparral ' , Purshia- -tridentata, which give to the scenery a wierd and desert asmid., p. 152). Overgrazing was apparently evident in the field area by the late 1870's. The mouth of the Ashnola River, where Dawson notes the presence of Artemisia trifida (Artemisia tripartig) , marks the approsinate west- ward limit in the Sirnilkameen Valley at the present time of the iower grassland dominated by ---Artemisia - -tridentata. - Dawson alss dppears to have seen ---Artemisia trifida in the Okanagan Valley, along the shore of Osoyoos Lake, for Macoun (1883) records this location for the species, and gives Dawson as the source. Althozgh Arteriiisia- -- -trf~rtita .- is much less frequent thhn -Art2m;siz ---tridentata in ;~;~chaf thf; arca at the present time, these observations appezr to :ndicctc that it was the more common of thc two in the 18701s, and may have been the pr-i ncipal shrubby 'sagebrush' of the area. Macoun's recognition of Artemisia tridentata.- at Lytton in I875 appears to be the firsr definite reference to the species in the Province. The locatim still marks the approxi- mate southern range boundary of the species in the Fraser Canyon. 138

A further comment on the lower Okanagan Valley may Se found in a provincial settler's guide for 1877-78: Near the point . . . where the boundary 1 itle intersects the Okinagan (sic) River flowing into the Colmbia, the cccri?try begins to assume, in its general features, a very ster-i'le character. An arid and stindy region, aln;ost tropical in its temperature, replaces the rich scenery through which we have been passing. Crossing the frontiei- into tha lJni ced St~tes territory, as we descend the Oki nagan towards the Go7 urhi a, this character becomes more general. The alluvial bottoiits alone, where there is natural irrigation, are susceptible of culture; the main feature of the prospect is a torrid waste of sand, in which the wormwood, at-d other varieties of the ---Arteini s-ia , the cactus, and other vegetation pr3per to sin~i1 ar wastes of remote volcanic snd diiuvial ~rig-in,alon~ find nutriment. We have entered, in short, upon the north-western angle of the Great American Desert . . . the vast 'Sage Barrens ' 1i e extended before the travel 1er (Anon, 1877). By 1883, Osoyoos Lake was described as being ". . . surrounded at a distance of two or three miles by mountains arld hi?1s. 1he inter- vening space is a sloping plain of sand and sage brush . . . . The region round about is quite destitute of timber, and the whole aspect is one of barrenness" (White, 1951).

The general impression conveyed by -ct~escre~orts is one of i ncrea.si ng overgrazing and rep1 acement by various species of Artemi sia throughout the decades of the 1860's and 1870's. It is difficult to assess how much of the iandscape was s3 sffected. Most of the comments concern the imnedi a te vi ci ni ty of major roads ; in, more inaccessi b! e areas the changes may have been slower, or less dramatic. Although the taxonomy is uncertain, it would appear that Artemisia-- frigida was the principal invader, but that other species were also involved. The apparent replacement of bunchgrass by -----Artemisia frigida may be partly illusory. This is a plant of rather small stature, rarely exceeding 40 to 50 cm. in height, and may have been commonly overiorrked cn ungrazed sites. The speed of the apparent replacexc t ji~p15~,at least, that seed sources were readily available, and that the preyrazing population was substantial. One shrubby species of -Artemisia appears to h~vebeen common in the ares by the mid-1890's. In 1895 a correspondent travel 1ing through the Okanagan-Simj 1kameen area noted that the 'sagebrush' began at Keremeos, and commented on ". . . the great hills and sayebrtish . . ." surrounding Penti cton (Vancouver Provi nce, July 6, 1895, p. 426). Invasion, however, appears to have been an ongoing pi-ocess for some time thereafter. Camsell (1914) wrote of the White Lake area in about 1912:

All the central and lower parts of the crea are open and free from any growth of timber . . . . The whole area of the csal field was once an excellent grazing ground for cattle: but so many cattle have been allowed to range over it that the grass which formerly covered it is being replaced by sagebrush. It was noted earlier that most of the Artemisia tridentata popu- lation in this area appears to have established sicce 1958, following a - period characterized by relatively low densities. I here is evidence, then, ef at least two distinct invasion events in this area., although not necessari ly i nvasions by the same Artemisis species,

By 1918 _Artemisia tridentdJt was sufficiently conmoc for Whi tford and Craig (1918) to define a sagebrush vegetation type, occupying the lower Okanagan Valley, couth of Okanagan Lake, and the Similkameen Valley below Keremcos. Photoq-aphs taken near Cawston in 1919 show a landscape dominated by large, vigorous plants of Wemisia ---tridentata (Figs. 5.2a and 5.3). Some of the plants taken in the age s3rnpIt. for Figs. 5.2a and 5.2b - Cawston, near Ibilth of El i'nd \:an's Creek, iooLS ng west,

1919 (above) and 1975. -Artemisia-- -- -.tridcnta-i:? .. -. - - -. --- ir! fore- ground of older picture. Figs. 5.3 and 5.4 - Caws ton, louki ng southwest. The Artemi sia -tridentata cover of 191.9 has been replaced by orchards. this study were already well established at the time these surveys were done, and at least one of them dates from the 1890's.

I I I. -.Documentary Records : F-- ire His tory

In treating this body of historical materia7 one fitids almost no direct references to fire in the grassland or the higher elevation forests during the nineteenth century. There are, however, abundant references to indirect evidence, chiefly in the form of burned areas within the forest, during and after this period. Whereas the traces of forest fire are persistent, as burned s trllnps at16 even-aged second growth, the evidence of grassland fire is ephemeral, and may vanish in a few weeks. As most of the observers were in the area for ongy a limitcd time, and so were unlikely to actzdlly witness fires, the absence of comment on fires in the grassland cannot be taken as evidence that such fires were uncommon.

There drc a few direct references, In 1831 Simpson reported of the valley of the Colmbia River between Colville and Fort Okanagan that:

"The drought had, as usual, parched the whole country, which appeared to be pretty gz;7erall;/ on -?-ire wherever there was arything to burn; and the atmsphere w2s so charged witi~smoke that we v;e,v unab;e to distin- guish objects even at a short distance" (Spencer drid Pollard, 1937). The Sherman party of 1883 also referred to fire in the grassland.

Of an area eighteen r~ilessouth cf Osoyoos Lake, it was observed that they travelled '\ . . most of the way wi timut timber. The country is rolling and mostly covered with grass, large areas of which have been recently burnt" (White, 1951). Most of the comments, however, refer to the occurrefice qf forest fire, and most of the evidence fs indirect. The earliest refer- ence in the Field area is by Dawson (1878) : "Both branthes of Cherry Creek . . . are bordered immediately by high rounded niountains which have at one time been for the most part densely wooded, but are now, owing to the spread of fires, covered with almost impenetrable windfalls." A simflar observation was made in the north Okanagan area by

Hagan (1288): "The tiaher . . . did not look as of much value; in fact the whole country has been badly overrun by fires at different times." Dawson (1895) makes a similar con~mentwith respect to the Kamloops area. He observed that nuch of the lower grassland was being fenced for wSnter use and, on the higher ground, great areas 04 windfall, the product of ". . . the recurrent tires," and a consequence of the carelessness of both Europeans and Katives. Pido (1952) has described a destructive range fire which swept the North Enderby section of the North Gkancigan ared in May, 1909. There is some etidcnce, however, that by this time the frequency of such events was declining. in the report of the provincial Minister of

Agricul ture for 1900, the rcpresentat-ive for ,he lwer 1ho:npson area is quoted : No fires in this distr-ict ;uch as there ~isedto be in earlier times. Then :hey were, undoubtedly, purposely caused by the natives with the object of burning off the old grass, which otherwise was not touched froin year's end to year's end. In consequence, cottonwood and other deciduous trees have sprung up in many places where for~er1.ythere was nothing of the sort, so continuously was the grouna burnt over (B.C. Dept. of Agriculture, 1900, p. 35). It is probable that many fires in the Thompson area after 1885 were caused by sparks from railway locomotives. Nelson and England 144

(1971) have reviewed some of the literature relating to fires from this source on the Prairies, and early conditions f n the Thompson Vzl ley were probably similar. In 1902 a forest fire at Lillooet was ascribxi to Native burning:

These fires were no doubt caused by Indians, v;ho set fire to the berry buskes, after they gathered the berries, to ensure a good crop the following year. Indians have told me that they have always done so . . . . These fires, hcwever, do very little damage 5n this part of the province to green timber-- merely burn the foliage but do not kill many trees (Report of the Ninister cf Agriculture, 1902, p. 222). Similarly, MacFie (1865) coi~ments that the Natives of the interior used fire to catch grassh~ppers: "Sometimes thc grass and weeds around are set on fire, so that they are disabled, and afterwaxis picked up." There are indications as weil that some fires during this period were i ntent-ionally set by Europeans. Wh-i ticord ar,d Craig (1918) observed that: " . . . the grass 1ands of the provi nice have been much extended through the complete destruction of the foi-est by fire," and that ground fires were apparently frequent in the yel!ow pine (Pinus ponderosa) vegetation type. They suggested that ". . . the prospector welcomed fire," to expose the rocks, and that the laws agzinst widespread burning, of 1884, had 1 ong rernai tied unenforced. - I he annual rep~rtof the Provi nci a1 Coinmiss? cner for Grazi ng , for 1919, aSsc spzaks of intentionai burning. The report expresses concern about the practice of burning high elevation ranges, but observes that ". . . the stockmen as a rule hold the opinion that the lodgepole or jack pine areas should be burned . . .", because they believe that the forage is improved as a result (E. C. Dept. of Lands, Annual Report, 1919). Ormsby (1931) alludes to widesprezd range burning, &in& at control 1i ng invasion by trees, and encouraging the bunch::rass.

The reports of survey crews working in thc study arm in the period i914 to 1922 include many references to past ma recmt fires.

This work invalved a photo-topographic survey of the area, of which some of the pictures have bee!; reproduced below. In 1915 a party working in the central and northern parts of the Okaliagan Valley repcrted that a triangulation station located ". . . during heavy srnoke last year . . ." had tc be moved. Other passages include: "During Axjust 15, 16, 17 there was more or less rafri in the vicinil;~,accompanied by heavy thunder and 1-ightning, insomuch that trees were struck and ignited in the loca- lity, and the air soon became smoky" (McCaw, 1316, pp. 108-110). "A large fjre swept portions of the (Mission) plateau years ago , . . many areas open, same occupied by standing dead timber . . . . The parts 1eft by the fire are usually of a park-1 i ke character" (Ibid.). F. H. Latimer was working in the Okanagan F?1ls-White Lake area

Much of the lower slopes are open bunch arass rafiges with a varying growth of sage and greasewood (Pursh'a- lridentata). . . . In most cases the pasture ranges secn were in fdir condi- tion, tho~ighthe \Jar,: season has been a pa;-t'c~lzi-1q dry one, and foresx fires were ai frequenc occurrence . . . (latimer, 1917, p. 39).

The survey was extended to the south O!:anagan in 1918: The entire area south of the upper part of Ellis Creek . . . has been the scene of fires in years gone by. Iluch of the country is covered with a tangle of windfalls . . . . Inter- mingled with this is a growth of small jack-pine and spruce (McCaw, 1918, p. 82). Similar reports come from the survey operatsons in the Lower -. Similkarneen and Okanagan areas in 1919 and 1920. ID,? partics complain frequently of time lost through smoky conditions, which rendered photo-

,graphic work impossible. One crew was driven from the east side of

Osoyoos Lake by a forest fire.

The survey by Whitford and Craig (1918) encountered much the

same conditions. Of the Okanagan Valley they wrote: "This basin has

been badly burned, especially on the uplands. These areas are restocking

with lodgepole pine (Pinus contorta) or with this species mixed with

Engelmann spruce (Picea engelmanni ) , Douglas Fir (Pseudotsuga menzi esi i)

and in places larch (Larix sp.)." They estimated that 55 percent of the

basin was occupied by young growth in 1918. The comparable figure for

the Thompson-Nicola area was 62 percent.

Some indication of the temporal changes in fire frequency in

this area comes from Smith and Henderson (1970), who have assembled

data on the stand age structures of the forests in the southern part of

the province. The data (Table V.l) are in the form of areas of particu-

lar forest types established in particular periods. Establishment is

assumed to follow stand destruction by fire, and the data thus provide

a fire history of the area. The outstanding modal age class is that of

the period 1897 to 1917, followed, in terms of acres per year, by the - periods 1917 to 1937 and 1877 to 1897. Low values for total acreage,

and acres per year, characterize the period 1937 to 1957. Many of the

older figures are low as well, but direct comparisons with more recent

times are difficult, as many areas may have been burned more than once,

and earlier fire occurrence may be greater than these data imply. There

is some evidence, however, of an increase in fire frequency during the

early settlement period, and of a recent decline. As the pre-settlement TABLE V. 1

Forest Age Structure and Inferred Fire Frequency

Pinus Ponderosa and Pseudotsuga rnenzies3i South Central Interior Period ria. cf 1000's of 1000 Acres 1000's of 1000 Acres Es tab1 i shed- --Years Acres per Year--- Acres per Year

1937-57 2 0 2G 1.3

1917-36 20 168 8.4

1897-1916 20 344 17.4

1877-96 20 88 4.5

1857-76 20 40 2.0

1837-56 20 38 1.9

1797-1836 40 140 3.5

1707- 1796 90 347 3.9

SOURCE : After Smith and Henderson, 1970. sources of ignition would probably remain relatively stat?e through the early settlement period, it is probable that ary increase in fire frequency during this period is due to the act~vitiesef European man.

Grasslands preserve no such record of fire hjstory, but it may be possible to extrapolate frcm these forest data to the adjacent grass- lands. In order to make such an extrapolation, it is necessary to know the ratio of forest acres burned to grassland acres burned, 2nd whether this ratio itself has changed over time. This ratio may be computed from data published by the British Columbia Form t Service (B. C. Dept. of Lands, Forest Branch, Annual Reports, 1915 to 1969). These data (Table V.2) record areas of forest and grassland burn2d by yczr and forest distrfct. Thex data are diffi- cult to coinpare directly, tor reporting areas were apparent?y changed twice, once in 1925 and once in 1933, and reporting efficf ency has probably varied over the period as well. These difficui ties may be partially overcame, hoivever, by cowputing the ratio of grassland acres burned to forest acres burned per year. These values are shown in Figure 5.5, plotted on a logarithmic scale, as a time series. The ratio may be seen to decline, from a mean of 7.57 for the pericd 1914 to 1924 (Vernon district), to a mean of .455 for the period 1958 to 1968

(Kamloops district, inclliding mGcn 07 tile forfiler Vernon district), a difference of about sixteenfold. These data must be treated with conie caution. The forest service did not have a 1ztye staff in its early years (MacDonald, 1929), and there may have been sorce tendency to underestimate the extent of forest fires in remcte areas, some of which rnay never have been reported at all,

TABLE V .2

Forest and Grassland Fire, from 1914 to 1968

Grassland Forest Ratio Grass 1and Forest Ratio, Fire Fire Grass1 and/ Fire Fire Grass1 and/ !ar- -(acres- ) ----(acres) -Forest - - Year &cr.es) -(acres) -Forest

VERNON DISTRICT MMLOOFS DISTRICT (cont 'd)

SOUTHERN INTERIOR

SOURCE: Data from B.C. Forest Service Reports, 1915 to 1969. resulting in somewhat inflated ratios. However, the data drr i~nplythat Smith and Henderson's estimates of f~restacres burned in the period

1897 to 1917 were probably easily exceeded by the extent of range fire in the same period, and that the extent of thr recerit decline in fire occurrence which their data record is probably conservative in compari- son with the decline in range fire over the same period. It may be concluded that grassland fire ms relatively common during at least the latter part of the early settlener~tperiod, and has

declined since. An exact date for thiz kcline is difficult to estab- 1ish, and may ha*~evaried from place to place according to the degree of settlement (and hence the consque~icesof wildfire), and the attitudes

of individual landowners. However, on the basis of these data, it is

possible to prDpcse the period from perhaps 19C0 to about 1930 as one which saw a relatively dramatic decrease in the frequency of range fire in this area. Of more importance is the question of a possible increase in fire frequency follawing European settlcmcnt. Such an increase is suggested by tk,e forest age structure data, hut these will naturally tend to under-represent fire frequency in the earlier period. This problem krill be taket ~p again in Chapter VI . A few records of fire freqwncy are availabie from other areas. Houston (1973) exmined fire scarred trees in the Ye1 lowstorie area, and estimated the natural fire recurrence ititerval to be about twenty to twenty-five years. He postitlated that recent fire control has led to an increase in the abundance of cw-iferous trees and sagebrush, and to

a decl i ne in aspen. Cooper (1950) c-i tes evidence of a mean fire

recurrence interval of only 4.8 years -in -Pi.- -nus - pond~rosa------stands i ri the 152 southwest. Weaver (1974) cites estiinates of fire frequency, based on fire scars on old trees in Washington and Oregon, wrying from eight to eighteen years on average. These estimates are prcbably conservative, for not all fires leave fire scars, but ~0~2of them probably include data from the early settlement period when frequencies rllay have been abnormally high.

Such fire f requerici es , if typical of the study area, must have been eff~itivein checking the growth of the Artemisia -trident.ata popu- lation, a.nd in shifting community don;! name to the fire tolerant grasses, and tc! the more fire tolerant species of Artemisia. This hypothesis will be examined in the following chapter.

IV. -Photographic-- - -- Evidence

So~ne further data on vegetation change in the study area come from the survey photographs taken in 1919 (Figs. 5.6a to 5 .X). These are shown paired with photos of the same areas taken in the summer of

1975. Difficul ties experienced in re1ocati ng the exact canlera stations account for the slightly different views provided by the 1975 photos.

It was hoped that comparison of the two sets of photcs, taken fifty-six years apzrt, would provide some data on vegetation change, particularly with respect to Artemisia tridentata- abundance, over the period.

Specific points are treated in the photo captions.

Several conclusions aFpear to be justified on the basis of

this ixateria I. In geriei-al, there has been little change in the position

of the lower tree line, or in the position or extent ~f isolated groves.

In many cases, the same trees can be identified in both pict.ures; in

some of the early photos they appear to have been relatively young, for

there is often perceptible height growth over the interval. This would appear to indicate that many of the trees depicted in the 1919 photos had established during the preceding decade or two. In some places

(e.g. Twin Lake), there seems to have been some slight increase in the extent of tree cover since 1.919. Cooper (1960) has shown that fire

imposes severe limitations cn recruitmeni in Pinus po~derosa. The photographic evidence of forest encroachment, then, tends to support

the hypothesis of declining fire frequency in the period after about

l9O8, which was developed earl ier.

Apart from the series of photos from Cawston, there are few identifiable plants of P,rternisia tridentata in the views from 1919, although the texture of some distant areas suggests the presence of a shrub community of some sort. Most of the old camera stations were sufficie~tlyfar above the valley bottom that the presence of -Arteinisia

--tridentata in the foreground is unlikely, even at the present ti:ne. Camera position r~lay accocrnt, as ;~el7, for thc absence of signs of severe overgrazing in most of the photographs. V. --Summa=

A number of tentative conclusions may be drawn from this materl'al. Artemisia tridentata- appears to have been much less abundant in southern Lri tish Columbia during the latter part of the nineteenth century than it is today, a1 thcugh such a conclusion is based, to a large extent, on negative evidence. However, the species was present in the province, at least from the mid-1870is, when Macoun records it from Lytton. The species appears to have bxome relatively common and wide- spread by about 1920. ---Artem-isia tripartita appears to have been of relatively greater importance in the area during the latter part of the nineteenth century, judging from the fact that Dawson (1878) records this species, but not the larger and more conspicuous -Artemisia tridentata. As many of the available observations refer only to 'sagebrush', it may be that Artemisia triparti ta was the common shrubby Artemisia present in this area at that time. Artem-isia frigida appears to have been tiiuch more abundarit in the area duri~gthe nineteenth century than at the present time. Its relative scarc-ity now may be due, in part, to grazing pressure. Such a conclusion would bc consistent with the observations of McLean and Tisdale (1972) on the exclosure studies at Karnioops. Fire appears to have been relatively common during the latter half of the nineteenth century and the first decades of the twentieth, and to have shown a gradual decline from about 1900 to the present.

As the observations of Whitford and Craig (1919) and others, on forest age structure leave little doubt that much of the area was burned in the recent past, the absence of contemporary nineteenth century refer- ences to fire must be considered an omission on the part of the observers, rather than evidence that fire was rare. Such a conclusion is consistent with the relatively low abundance of the shrubby ---Artemisia species in the area at the time, and with the recent encroachmmt of trees at the grassland border. Lightning and Native burning may have been responsible for fires in the area in pre-settlement and early settl erneat times. intenti ma1 burning by Europeans, aftw 1860, may have resulted in some increase in fire frequency over that of the pre-settlement period. The existing data OP forest age structure suggest such a,n increase, but the data must be considered inconclusive. Increased fire during the early settlement period would tend to reduce the size gf --Arternisia trident=, and perhaps

Artemisia tr.ipartita-- popu7ati~ns,and perhaps lead to an increase, at least in relative terms, of Artemisia frigida. This hypothesis will be treated in the following chapter. CHAPTER VI

THE PALEOECCLOGI CAL RECORD

I. ---- Introduction

The purpose of this chapter is to employ the paleoecological record, particularly that provided by pol len analysis , to explore the former abundance and dynamics of the Artemisia Jridentata population within the study area, and to provide data which will permit some explanation of any changes in abundance which have occurred, particularly in the period since European settlement. The exist-incj historical record indicates that ktemisia tridentata, although present, existed in lower abundance during the latter half 07 the nineteenth century than at the present time, and that the abundance of the species on rangelands within the study area increased to present levels duri rig or just prior to the present century. If th-is is Lrw. the increase shouid be recorded by an increase in the abundance of pollen 05 this species in the recent portion of sediment cores froin tr:e study area. The pollen record may thgs serve as an independent check on the recent history of the population revealed by historical dccurnents, as well as providing data on longer term popula- tton chafiges. Such data niay also serve to test the conclusions of

Chapter IV, for if the inference that grazing disturbance is not a necessary condition of population maintenance is substantial 1y correct., it may be expected that some evidence of high population levels in the

period before the introduction of domestic cattle will be found. Similarly, these data should provide the means to verify the recent

fire history obtained from documentaty sources, to expand that history

to the period before such sources are available, and to test the infer-

ence made earlier about the effect of fire on the Artemisia tridentata

population.

The chapter begins with a general discussion of palynological methods and sampling design, followed by a discussion of pollen taxonomy

and pollen dispersion in the genus Artemisia. The substantive portion

of the chapter is divided into three sections, one for each of the

sediment cores discussed. The results of the analysis of these cores

are discussed within each of these sections, and summarized in a final

section.

A. Techniques of Pollen Analysis

Good general reviews of the principles and methods of pollen analysis may be found in Faegri and Iversen (1975) and in Davis (1969).

Many of the methods employed in this study are relatively site specific,

and are best explained in-context with the data and depositional

sequences to which they were applied. The material in this chapter is

presented as a series of sections or modules, each with a brief discus-

sion of the specific methods used. This section will attempt to lay

the general groundwork for some of the specifics which follow, and to

detail only those methods which are common throughout.

Pollen slides were prepared from fresh material and sediment samples using a technique similar to those described by Faegri and Iversen (1975) and Kummel and Raup (1966). A 0.5 to 1.0 gram sample of wet sediment was placed in a 15 ml. plastic centrifuge tube and succes- sively washed with the following reagents: 5% HC1 to remove carbonates 5% NaOH to remove humic acids and deflocculate the sample - heated in a boiling water bath for about four minutes 50% HF to remove silicates - B.W.B., four minutes 5% HC1 to remove flurosil icates glacial acetic acid to dehydrate a 9:l mixture of acetic anhydride and concentrated sulfuric acid to hydrolize cellulose materials - B.W.B., one minute. Addi tional procedures i nvol ved sievi ng the sampl e after deflocculation and decanting the sample several times to remove sand. After each step, the sample was washed in distilled water to remove chemical residues and reconcentrated by centrifugation. The residual material was stained with safrani n, washed in tertiary butanol , and mounted in silicone oil with a viscosity of 2,000 centistokes. The procedure for reference material was similar except that only a few anthers or flower heads were needed, and the hydrofluoric - and hydrochloric acid treatments were omitted. The pollens were identified and counted in repeated transects across the microscope slide on which the material was mounted. Counting was performed at a magnification of 400X, and the traverses were spaced at 2 mm. intervals. Counting proceeded until a sum of 300 or more grains was obtained. If the end of the slide was reached before the minimum count was achieved, the process was repeated using the one mm. divisions not sampled in the first pass. In extreme cases a second or third slide was prepared. The result is a tally of pollen grains in various taxonomic groups, from which estimates of the proportion of each taxon in the sample may be readily cal cul ated. In addition to the pollen content, sample material was rout i nely processed to determine water content, as a percentage of oven dry weight, and organic content, as the percent age loss on ignition at 450 degrees C.

B. Data Representation Pollen data have been presented in the form of traditional 'relative' pollen diagrams, in which the abundance of an individual taxon is represented as a percentage of the sum of the principal polien types in the sample, and in other forms, which may be designated ccllectively as 'absolute' pol len diagrams. These other 'absol ute' pollen represent- ation forms nay be classified into pollen concentration and pollen deposition rate types. The concentration form expresses polien abun- dance as grains per unit weight or per unit volume of sediment, or of some fraction of the sediment. Both total weight and sediment fraction forms have been used in this study. The procedure used to obtain these estimates was siniilar to that described by Mailer (1972). Briefly, it involves the add

of Tilia pollen with a concentration of 5,270 grains per cc. as deter-

mined by 100 trials with an haemocytometer. Earlier trials with

Lycopodium spores and fine plastic beads were unsuccessful, as the

grains were found to fracture when the suspension was stirred.

Other procedures for making pollen concentration determinations

have been discussed by Maher (1972) and Peck (1974). Peck found that

the exotic pol 1en procedure used here gave somewhat higher coefficients

of variation on duplicate samples in comparison with the commonly used

'weighing method', but noted that the latter is more prone to operator

error, and tends to underestimate true concentrations due to losses in

processing. She recommended the use of an exotic addition as a control.

Maher (1972) prefers the exotic method, on the basis of simplicity, and

believes that the attainable accuracy is quite as good as with the more

complex weighing technique.

Pollen concentration diagrams substitute sediment quantity, or more precisely the sediment accumulation rate, for the pollen sum as a

basis for calculation and comparison, and are thus free of the statis-

tical dependence among taxa which resul ts from the 'zero sum' character of percentage calculations. This advantage is frequently offset by the

fact that pollen concentrations will vary with the sediment deposition

rate, making the resultant diagrams as difficult to interpret as those

based on percentage calculations. Because of the different mode of

ca1cul ati on, however, concentration data frequently provide a useful

check on the percentages, and may provide insights into the data which would otherwise go undetected. Pollen concentration data therefore have been presented in conjunction with percentage estimates whenever possible. An attempt to prepare a pollen deposition rate diagram for one of the cores is discussed in Appendix I.

Fire occurrence in the area over the period represented by the pollen cores has been estimated by obtaining quantitative estimates of the amount of fine charcoal present in the sediment samples. The first quantitative work of this kind was that of Swain (1973), who demon- strated that the abundance of fine charcoal in sedimentary sequences can be used as an index of local and regional fire occurrence. The charcoal which is found in such situations is readily identified as opaque angular fragments, dense black or brownish in contrast to most other organic material, which stains readily, with wood structures some- times present in the larger pieces. Swain quantified the abundance of these fragments by estimating the area which they occupied on the sampled portion of the slide. This procedure is laborious, and possibly inaccurate, for the fragments are commonly very irregular in shape. The procedure adopted here was that of a simple count of all fragments with a maximum dimension greater than ten microns. Charcoal tallies are treated as other taxon counts, but are not included within the pollen - sum.

C. Sampling Design

Three types of pollen sample were taken within the study area.

Modern reference material was collected from living plants of Artemisia tridentata, Artemisia tripartita, and Artemisia fri gida, and from a variety of other species in the study area and in the Nicola and Fraser

Valleys. The Artemisia collection was augmented with material obtained from the Provincial Museum, in Victoria. This material has been pre- served as a permanent reference collection, and was used as a guide to the taxonomy of the fossi 1 materia1 . Samples of the modern surface soi 1 within the study area were processed to determine the relative abundance of Artemisia pollen in the modern pollen rain, the dispersion of Artemisia pollen from source areas, the spatial correspondence between Artemisia pollen abundance and the regional abundance of the species, and to test certain inferences about the pollen taxonomy. One of these samples consisted of a series of soil samples along a line transect running from the edge of an iso- lated stand of Artemisia tridentata, while the other consisted of a series taken along a forty-mile transect down the Simi1 kameen Val ley.

Fossil pollen spectra were taken from sediment cores from three lakes within the study area (Fig. 6.1). With the exception of the

Okanagan Valley, which was not sampled due to its highly modified land use, suitable lakes are not common within the driest parts of the study area, and the choice of sample sites was limited. The three lakes were chosen as part of a transect from dry to mesic conditions; one near the lower end of the Simil kameen Valley at Richter Mountain (Richter Marsh), - one slightly below the present a1 ti tudi nal 1imi ts of Artemisia- tridentata

(Twin Lake), and one slightly above those limits (Mahoney Lake). Attempts to isolate pollen from seasonal water bodies, such as the White Lake playa, were unsuccessful. Figure 6.1. Pollen sample sites and transects. I I. Artemi sia Pol 1en Taxonomy

The pollens of the three species of Artemisia common in the study

area are very similar morphological ly. A1 1 are approximately spherical , tricolporate, and have thick exine walls, thinning towards the poles, with prominent columellae giving the wall a multi-layered appearance.

The grains of Artemisia tripartita have slightly thinner walls, and a more delicate appearance than those of Artemisia tridentata, and this

tendency is accentuated in grains of Artemisia frigida, but the differ- ences are so slight, and the gradation so continuous that these characteristics cannot be used as reliable taxonomic features.

Pollen size has been used in many studies as a taxonomic tool within closely re1ated groups (Hansen, 1947; Martin, 1963; Whitehead

1964, for Pinus and Clausen, 1962 for ~etula). Hansen (1947) attempted

to assign individual grains to particular species on the basis of size, but this approach has been criticized by Mack (1971) on the grounds that size range overlap renders such determinations suspect, and that intra- specific variation in Pinus pollen is sufficient to produce pollen size changes independent of specific change.

The use of pollen size as a taxonomic tool in Artemisia was

investigated using reference material gathered in the southern part of

British Columbia. Pollen size frequency distributions were obtained by measuring 50 random grains from each of seven or eight individuals of each species. Measurements were made with the aid of an eyepiece micrometer to the nearest half scale division, or about 1.25 microns.

Measurements were made on the longest visible dimension, for the grains tend to orient randomly on the slide, and are difficult to turn for measurement purposes. Comparison of polar and equatorial dimensions within populations revealed no significant differences (Xpolar = 10.24 ocular units, Sp = 0.656, N = 27; Xequatorial = 10.26 ocular units,

Se = 0.578, N = 27; t = 0.1165).

The resultant frequency distributions are shown in Figure 6.2. The three species have distinct, but overlapping size distributions, with a ranking of Artemisia frigida, Artemisia triparti ta, and Artemisia tridentata in order of increasing size. The frequency distribution of Artemisia tridentata is sl ightly bimodal, and significant differences exist between plants in the same locality (Table VI.l).

TABLE VI.1

Artemi sia Pol 1en Size Data from Modern Reference Material

Artemisia friqida Artemisia triparti ta Artemi sia tri denta ta d S N % S N % S N

8.20 .571 50 9.32 .523

7.69 .588 50 9.19 .494

8.17 .726 50 8.89 .641

7.91 .589 50 9.14 -581

8.01 .484 50 9.22 .686

8.04 .638 50 8.70 .598

7.82 .569 50 8.39 .600

7.91 .636 50 * = mean size i n ocular units N = sample size S = standard deviation NOTE: one ocular unit - 2.5 microns.

178

Because the size distributions overlap, it is not possible to assign single grains to a species with confidence. Arternisia---- grains within the fossil samples have been tallied as a series of size measure- ments, from which frequency distributions or population means have been calculated. It was hypothesized that the mean size of an assemblage of

-Artemisis-- -- .- grains would provide a useful index of species cornposition within the genus population; 1args values signifying a re1ativeiy 1arge proportion of Artemisia tridentata, ac3 small va1 ues a re1atively greater proportion of Artemisia tri partita and Artemisia -frigida. - Some tests of this hypothesis are presented below. Mean size data have been supplemented by frequency distributions , expressed as the abu~danceof grains in specified size class groupings, so that a distinction may be made between mean size changes which result from changes in large grai? frequencies, and those which resul t from changes in small grain frequencies.

111. The Modern Pollen Rain: Surface Sample Data

A. Loml Effects-

The pollen content of surface soil samples was analyzed in an attempt to document :he dispersion of --Arteniisia tridentata pollen from an isolated source. It was hoped that the res1:lts would serve as a guide to the collection of surface sa~pleson a regional basis, and provide inforruation on the degree of local effects which might be expected in fossi 1 zsset~blages.

The site chosen was an isolated stand near Kererneos. Samples were collected at intervals along a transect froin within the stand edge to a distance of 150 metres outside of it. Samples were obtained as ten random 'pinches' of soil and duff along a line at right .angles to the main transect, the randomization taking the form of a random number of paces between samples, with the sample location marked by the toe of the boot at the last step. The samples were prepared as fossil samples, and the abundance of Artemisia pollen was determined as a percentage of the arboreal taxa present. The results are sh~wnin Figure 6.3. The data show a strong negative correlation with distance from the stand (Rs = - .9524, p < .01). The presence of one sample point with a negative distance from the stand edge precluded the use of a logari th- mic transformation on the X (distance) axis, and the regression line shown has been fitted by e-ye. The curve appears to become asymptotic after about 130 metres. The model suggested by Tinsley and Smith (1974), which expresses pollen percentages as a linear function of the reciprocal of the distance from the source, did not provide a satisfactory fit to these data, but they too found that the curve became asymptotic after about 109 metres. It is evident from these data that departures from the regional pollen percentage caused by particular stands of --Artemisia tridentata will probably affect only a very local area. The presence of local stands should not, in general, produce marked effects in fossil cores frcrn lakes of even moderate size.

5. ---Regional Effects A further series of surface samples were taken ta evaluate the behavjuur of the Arternisia pol len percentage, and the mean Artemisia

pollen size at a regional scale. Pollen samples were obtained by the ' random pi nch ' method a1 ong a transect beside the trans-Canada highway through the Simi 1kameen Val ley, from the campground at Stemwi nder, to

the United States border, a distance of about 64.5 km. (40 miles) (Fig. 6.1). The pollen samples were taken at roughly four km. intervals, and were prepared and counted as described above, to yield percentage Artemisia content, and mean Artemisia pollen size. Estimates of Artemisia tridentata abundance were obtained by making visual estimates of cover and density at half mile (0.8 'krn.) intervals along the length of the transect. The estimates were made on the basis of a four point scale, from 0, absent, to 4, very abundant. With plus and minus adjectives the entire scale contained twelve ranks. Repeat estimates on some stations, and the provision of photographic documentation of 'type' sites (Figs. 6.4, 6.5 and 6.6) give the method

some degree of reproducibility, but it does suffer from the fact that the estimates are necessarily based only on those areas within the field of vision. Attempts to estimate Artemisia cover from air photos were unsuccessful. The pollen data and the visual abundance estimates were compared - in an attempt to test two hypotheses. Because Artemisia tridentata is the most abundant species of Artemisia at these valley bottom sites, it was expected that the relative abundance of Artemisia in the pollen sample would show some degree of positive correlation with visual esti- mates of Artemisia tridentata abundance. Because the other species of Artemisia are more widespread than Artemisia tridentata, it was expected that mean pollen size would also show a positive correlation with the Figs. 6.4 and 6.5 - Visual abundance transect Station 26, west of Keremeos. Abundance class 2. Fig. 6.6 - Visual abundance transect Station 63, Site E of the age structure sample. Visual abundance class 3. The class rating is based on cover and density. The hoodoo on the valley wall behind is of lucustrine silt. visual estimates, with 1arge vean sizes predorfiinati ng in areas with abundant -~rienisia --tridentata, and smaller sizes predominating where Artemisia- tridentata was less abundant or absent, and relatively more of the ---Arternisia pollen found derived from the other s~ecies. Comparison was by means of the Spearman coefficient of rank correlation. The pollen data were compared to the average of the ranks of the seven adjacent visual estimate stations, centred on the poilen sample site. The results are shown in Figure 6.7. Correlation coefficients of .5262, between Artemisia percentage and the visual estimates, and .5151. between mean ---Artemisia pollen size and the visual estimates were obtained, both significant at the 5% level. The lack of a closer corre- spondence is believed to reflect the crudity of the visual estimation procedure, particularly in situations where the field of view was limited, and the difficulty experienced at some pollen sample stations of +ir!d-ing areas more than the requisite 100 metres from the nearest Artemisia -tridentata. The observed spatial variation is prob- ably much greater than would be found over time in a single lake basin, which represents a much more stable sampling device. In spite of this variation, we may accept the hypotheses that Artemisia percentage and mean Artemisia pollen size provide useful indices of the abundance of

Artemisia -tri den iata in this area.

IV. Fossil Pollen Spectra: Richter Marsh

A. Site Description and Methods

The pollen core from Richter Marsh is treated first, because it

- is the only core obtained in this study which is believed to represent most or all of the Holocene period in the study area, and thus provides

some necessary background for the more detailed material which follows.

The site is located at 49 degrees, 1 minute, 30 seconds N, 119 degrees, f 39 minutes W, in an area of natural grassland which is presently domin- ated by Artemisia tridentata. The depression from which the core was

taken appears to have originated as a shallow kettle in the outwash

W deposits which form the valley train. The basin has an area of about P 0.33 square kilometers, and receives the drainage of an area of about a 50 square kilometers. Slightly more than half of the basin has been C infilled, and is occupied by a marsh dominated by Juncus sp. The core

was taken from the centre of the marsh at the edge of open water with a

Davis sampler of the type described by Mott (1966). Samples were taken

at approximately 5 cm. intervals at the top of the core, and at 15 to k. 20 cm. intervals at depth, but the characteristics of the Davis sampler

make accurate depth control difficult, and the actual sample depths are - somewhat irregular. Samples were retained in labelled bottles, or plastic

bags for later analysis.

B. Results

The stratigraphy of the core site consists of 450 cm. of sandy

marl with occasional to frequent shell fragments, overlying 70 cm. of

dark grey plastic clay, overlying a stratum of fine gravel which was not

penetrated. The only other visible stratigraphy was a one to two cm. band of slightly darker material at about 45 cm. depth, which was later found to be relatively widespread in the vicinity of the core site. No material sui tab1 e for radiocarbon dating was recovered in several cori ng attempts, and stratum dates have been inferred, of necessity, from the pollen and sediment stratigraphy. (a) Pol 1en Stratigraphy A percentage pollen diagram for the site is shown in Figure 6.8. Because the pollen concentration data for this site appear to be strongly dependent on the sediment accumulation rate, only total pollen concentra- tion data have been presented (Fig. 6.9). For ease of discussion, the diagram has been subdivided into three major zones, and a number of subzones . The lowest subzone, R Ia is represented by a single sample distinguished chiefly by the abundance of an unusual small Betula type grain, tentatively referred to Betul a gl andul osa . The pauci ty of arboreal taxa except for Pinus and Picea, and the presence of the heavy clay matrix imply the presence of a late glacial environment. No pollen was recovered from the basal sample at 520 cm. and this stratum has been omitted from the diagram. - Subzone R Ib (450 to 400 cm.), again represented by only a single sample, is characterized by the decline of Betula and Picea, and the appearance of small amounts of Tsuga , Grami neae , Artemi sia, A1 nus and Salix, and a transition to the marl sediments which form most of the core. It may be considered transitional to Zone R 11. Zone R I appears to be comparable to Zone KB I of A1 ley (1976) from a site near Kel owna .

Fig. 6.9 - Richter Marsh, loss on ignition and pollen concentration data. Concentrations are for those taxa within the pol len su~n. Zone 2 I1 (400 to 260 cm.) is marked by an expansion of Picea,

Cupressaceae, Al!l!~sy Salix, Gramineae and Artemisia. The zone has been divided into t~osubzones, the lower of which shows higher amounts of

-- -- Picea, and lower amounts of Gramineae and Artemisia than does the upper one. The hiyh levels of Gramineae and --Artemisia in the upper subzone (R IIt) suggest a major expansion of the lower grassland at this time, and imply that the zone is comparable to zone KB ?b of Alley (1976) and to the peak in non-arboreal taxa recorded by Hansen (1955). Both of these workers found a stratum of volcanic tephra within the zone, Hansen near the middle, and Alley near the top. Alley refers the tephra to the

Mount Mazaina eruption dated at approximately 6,600 years B.P. No dis- crete tephra stratum was recognized in the Richter Marsh core, but pollen stratigraphic siniilaritfes suggest that a similar date is applicable.

The remainder of the core (265 to 0 cm. ) has been designated zone R 111, and has been divided into five subzones. Subzone R IIIa is marked by a relative expansion of Picea and Pinus, and a decline in

Gramineae and Artemisia, and may be roughly comparable to zone KB IIIa of Alley (1976). Subzones R IIIb and c show increased quantities of

Betula, Gramineae, and Artemisia, and are separated primarily on the basis of --Picra, which reaches low values in subzone R IIIb and of

Populus, which sho!i a rnin~rpeak in this region.

The lower boundary of subzone R IIId was located on the basis of a dramatic decrease in the relative abundance of Artemisia pollen, and an increase in the abundance of Tsuga and Pseudotsuga/Larix type grains. The boundary corresponds to the location of the stratum of darker material noted above, and lies immediately above a sample characterized by relatively high organic content (2.7% loss on ignition)

and high pollen concentrations (Fig. 6.9). On this basis, the upper

part of subzonc R IlIc has been interpreted as a recurrence surface

produced by a decrease in sedin~entationrate, and subzones R iIId and e

are judged to be the product of renewed deposition. Renewed deposition

at the sample site appears to have resul ted from the construction of a

low darn across the lake outlet. The age of the dam is unknown, but it

is certainly of post-settlement age, and the sediments of subzcnes

R IIId and e and perhaps part of the material below, are therefore

believed to have accumulated in the post-settlement period. The dura-

tion of the depositional hiatus represented by the recurrence surface

is unknown.

The lower boundary of subzone R IIIe was located prinia~ilyon

the basis of an increase in the abundance of ---Artemisia pollen.

(b) --The Artemisia Record: Pollen- Size Data

More detailed data on the Artemisia population are shown in

Figure 6.10. In zddition to pollen size data, the Artemisia to Gramineae

ratio (sane to grass ratio) was computed in the expectation that this would tend to index the ablrndance of --Artemisia within the grassland,

independent or' changes in grassland extent. Minimuri values for this

index are found in subzone R IIId, ar,d remain re?atively low in compari-

soi7 to the deeper parts of the core through subzone !? IIIe.

Mean ---Artemisia pollen size also shows minimum values in subzone

R IIId, after declining gradually through subzone R IIIc, and then

reaches a maximum value in the uppermost sample. The value at level 5

tias been omitted due to sinall sample size. Large rnean size values are

also found in zone K !I. Fig. 5.10 - Richter Marsh - Artemisia- detail. 193

The abundance of Artemisia grains within specified size classes

has been used to determine the source of the variation in the mean pol 1en

size index. Size frequency distributions of fossil and surface sample

Artemisia grains are generally smaller than those derived from fresh material ; i.e. grains of the largest size classes encountered in the

reference material were never encountered in the fossi 1 material, while

the fossil material contained grains smaller than any seen in the reference

collection. Although some of the smallest grains may derive from species

not included in the reference material, i.t is believed that most of the observed difference derives from the use of hydrofluoricacid on the

fossil and surface samples, as this treatment is known to cause some shrinkage (Faegri and Iversen, 1975, p. 105). The size classes used throughout this discussion are arbitrary, and have been chosen to achieve a relatively even division of the actual size range present. Three classes have been used: less than 18.13 microns (7.25 ocular units) ,

18.13 to 20.6 microns (7.25 to 8.25 ocular units), and greater than 20.6 microns. These classes will be designated small, intermediate, and

large, respectively.

In spite of the arbitrary size classes employed, the curves of - abundance within those size classes show a degree of mutual independence.

The significance of this apparent independence has been tested by com- puting the Chi square statistic for the grain frequency in each size class and in each pollen zone, as shown in Table IV.2. Zone R I was

omitted due to low frequencies. The calculation yields a value of 43.8, with 12 degrees of freedom, indicating a probability of less than .001

that these samples could have been drawn from a single population. It may be concluded that the arbitrary size class ab~lndancccurves do tend to index different populations, arid should provide a 1lscfu1 basis for interpretation of the mean size vatues obtained.

TABLE VI.2

Richter Marsh--Pol len Size Frequencies by Po1 len Size

---Smal 'l Intermediate -Large --Zcne 4 6 6 E 6 2 2 0 39 3 2 12 C I11 26 38 21 R 12 17 13 A

Chi square = 43.815 Degrees of freedom = 12 p < .001

Percentage abundance within the size classes is shown in

Figure 6.10. The upper part of subzone t? IIIc and the iower part of R IIId are dominated by grains of the small and intermediate size classes. Minimum values for all three size classes are reached in subzone R IZId, with the large and intermediate groups declining first.

Subzone R IIIe shows a small early peak in the abundance of the inter- mediate size class, but the surface sample is dominated by the large class, and the other two decline. (c) The Charcoal Record

Fine charcoal was found in abundance at all sample levels

throughout the core. Charcoal tallies, expressed as percentages of the

pollen sum, are shown in Figures 6.8 and 6.10. The pattern may be des-

cribes as a series of irregular peaks superimposed on a relatively

steady background rain. Charcoal is relatively abundant in zones R I1

and R IIIa, declines through subzones R IIIb and R IIIc, increases in a

series of jagged peaks in the upper part of subzone R IIIc and through

R IIId and declines in subzone R IIIe.

C. Analysis and Interpretation

(a) General Comments

These data indicate that some species of Artemisia have been in

the study area for much of the Holocene period; at least 7,000 years if

the correlation with A1 ley's (1976) data can be accepted. The expansion

of Artemisia and Gramineae in zone 11 has usually been interpreted as

evidence of warmer or drier conditions at this time, and has been core-

related with the 'Hypsithermal ' or 'A1 tithermal ' widely recogni zed in

Europe and elsewhere (Bray, 1971). There seems to be little reason to dispute this interpretation in this case, although the data presented

in Chapter IV indicate that warmer or drier conditions may not be the only possible explanation of an increase in Artemisia. Although Mathewes

(1973) found no evidence of Hypsithermal conditions at a site near

Vancouver, this may be explained in terms of the greater oceanici ty of that area. The large mean pollen sizes, and the abundance of the large pollen size class in zone R I1 indicate that Artemisia tridentata was probably a major component of the Artemisia population at that time. The decline in total ---Artemisja - in subzow R IIZd, and the low mean pol 1en sizes encountered tend to confirm cbe iir~pressionof shrub- free grassland, or grassland with Artemisia frisid2- a!:d ----Artemisia -- - tri parti-- ta , conveyed by the documentary records. Sinli l arly , i n subzone R IIIe, the increase in total Artemisia, and the narked increase in mean

----Artemisia pollen size, tend to confirln the widespread Smpressior! of a recent Artemisia- tridentata increase. The sharp minirnuin in Gramineae pollen, in the upper part of subzone R IIId may probak~lybe interpreted as resulting from overgrazing in the late nineteenth or early tientieth centuries.

The ---Artemisia ninirnun~ in subzone R IIid was apparently short- lived, and relatively unusual in comparison to the entire record. Total Artemfsia abundance, mean Artemisia pollen size, and the abundance of grains in the largest size class below subzone R IIId all tend to indi- cate a substantial Artemisia tridentata. population prior to European settlement. Although the maximum mean ---- Artemisia pollen size is reached in the surface sample, the total abundance and size class data indicate only a moder3te increase in --Arteinisia ----tridentata abundance above pre- sett1erne:lt levels, and a local population still substantially smaller than that of earlier periods, The high meai: size in the surface sample is due as much to a decline in the proportion of the ma1 1 and inter- mediate size classes as to an increase in the large class. The data appear to support the conclusion of Chapter IV, that heavy grazing is not a necessary cmdi tion of establ ishment and population maintenance of --Arteniisia -tridentata in this area. Grazing may, however, have played some part in the population changes recorded in subzone R IIle, by providing the necessary disturbed conditions for -----Artemisia ~r'cientata

establishm~nt,or by suppression of the other -Artsni sia species pr-esent.

The most remarkable aspect of these data is the Artmisia minimum of subzone R IIId, for it appears to be confincd to the early settlement period, and may be related to anthropogenic disturbance at that time. Although climatic factors cannot be eliminated as a possible cause of this feature, its post-settl ement position, and correlation with rel~tivelyhigh charcoal values suggest that it may owe its origin primarily to widespread burning. The following section is devot~dto an analysis and test of this hypothesis.

(0) The Charcoal Record:--- Correlations withmen-- ~ata A1 thwgh the fine charcoal counted in these samples provides evide~ceof an extended fire history in this area, the actual origifi of the charcoal is unclear. Local and regional, forest and grassland sources may all be represented, perhaps in different proportions at different times. The peaks may represent local conflagrations, and the steady background rain an integrated regional component, but smoke from forest fires has been known to travel great distances (Hare and Thomas, 1974, p. 184) and fine charcoal fragments may behave 5n a similar manner, so that some of the peaks riiay no; repussent local fire. Some constant influx from the local environment may also be expected, for charcoal is persistent in most soils, and may enter the deposition site

! as erosional detritus over long periods of time. Of major concern here is the mix of forest and grassland sources, fcr if most of the charcoa: found derives fro^ forest fires, it is unlikely to be of much value in explaining the observed pattern of fluctuation in the Artemisia population. The approach adopted here has been to search for correlations between the charcoal record and indica- tors of the condition of the grassland vegetation, particularly the

Artemisia pol len size data. Significant correl citions should demonstrate that at least a substantial fraction of the charcoal found derives from grassland sources, and demonstrate the effect of fire on the component Artemisia- populations . In order to reduce the complicat-ions produced by climatic change,

the analysis has been restricted to the ddta from zone R 111. Similar results were obtai iled from the entire data set, but the eff-ects of climatic change render the interpretation zomplex. Because the level of integration represented by the charcoal data was unknown, the curve was subdivided into a trend component, represented by a moving average over three sa~nplelevels, and the scaled deviatfons from that trend. It was expected that the two terms would tend to index, respectively, the long- term fire regime, and a short-term component of individual fires or series of individual fires. Correlations were sought between both the trend and the deviations and the mean Artemisia pollen size, the sage to grass ratio, and the percentages in each of the size classes. Spearman's coefficient of rarIk correlatio~iwas used as the test ctatistic. The results are shown in Table VI.3. The sage to grass ratio shows a significant negative correlation with the charcoal trend series, but no correlation wi tn the series of

deviations. Mean ---P,rtemisia pol 1en size shows significant negative correlation with the series of charcoal devi a tims, but no si yni ficant 199

correlatjon wi th the charcoal trend. These resul ts are in s~bstantial agt-eenerit with the data on recent fire effects presented in Chapter IV. Protracted burning tends to reduce the abundance of --Arteinisia within the grassland environment, whsle individual fires tend to reduce

---Artemisia tridentata abundance relative to the other species. The scale differences i~npliedby the different reactions to the charcoal trend and

deviations dppea r to ref 1ect the f i re to1 erance of the species i nvol ved ; the species with small pol len predominate after occasional fjre eve~ts, but these too are reduced under a regiine of repeated burning, and the

resultant changes in the mean pol 1en siie obscure the 1ong- term re1 ati on- k skip. In the set of corr-elations betweer1 the charcoal deviations and Artemisia size class abundance, oniy the large pollen class shows a B significant (negati ve) correlation, implying that inost of the response of the mean pollen size to chai-coal frequency derives from changes in the

Artemisia- -.trjdcn -- -- tata population.

TABLE VI .3

Ri chtw Marsh--Correlation Coefficients (Spearman's) Between Charcoal Values and Arternisia- Pol 1en Indices

Dependent Variable Zone TI I Charcoal Trend _Charcoal Deviations Mean pollen size Sage to grass ratio

% small Artemisis pollen % intermediate Ai'tmisia pollen % large Artenisia pollen * Significant at the 5% level. Thcsc wsuf ts indicate that a substantjal fraction of the chzrcoal present in the samples does derive from grassland fire, prob- ably close to the sample site, and that these fires have influenced the abmdance and species composition of Artemi sia i n these grass1 ands over an extended period of time. Promiscuous burning by early European settlers, implied by the high charcoal values in subzone R IIId, and by the available historical data, appears to be the most probable cause of the ----Artemisia mlinimum at that time, and the recent Artemisia increase, although possihiy influenced by grazing disturbance, may be related to fire suppressian in recent decades. These iirferences will be further tested and refined in the follohing sections. If these features of the population history of this species have any general, regional validity, it shoi~ldhe possible to deimnstrate similar. patterns at other sites within the field area.

V. Fossil Pollen Spectra- 11: Twin Lake

A. Site and Rethod

(6 Location and Sampling Twin Lake (44 degrees, 19 minutes N, 119 degrees, 44 mirutes W)

(Fig. 6 -1) is 3 pair of ma1 1 deep lakes at an ai t~xude of dliout 800 metres, which appear to have originated as lar~ekettles in the outwash fill of a narw~ivzlley. The lakes receive the drainage of about 36 square kilometres. They are ccnnected by a small stream, but the lower of the two has no surface ~utlet,the waters apparently passing through the sandy outmsh material and reappearing at the surface further down th~val leg. Af though most of the drainage basin is forested, the lakes are surrounded by grasslands containing Artenlisia tridentata at relatively

lo& densities. The large Artemisia tridentaQ population 2t White Lake (s~mplesites A and K) lies just to the east. The climate of the area

is somewhat inore mesic than that of Richter Marsh (R. Davis, personal comunication) and the site is close to the present range limit of --Artcmisia tridentata. The core was taken fro~the lower of the two basins, through 30 metres of water, using a freeze corer or 'frigid finger' of the type described by Swain (1973). The sampler is of the free-fa1 1 type, and the depth of penetration is limited by the depth of the water, the mass of the sampler, and the consistency of the sediments. The device is Filled with a freezing mixture of dry ice and alcohol, causing the sedi- ments to freeze to the outside surface. While suitable only for short cores, the device has the advantage of being readily used in deep waters fmm an unanchored boat, and of taking sediment cores which have been subject to a niinimum uf disturbance. The core was sectioned in the field and retained for analysis.

(b) --Datw The core was fomd, on recovery, to consist of a series of laminae

(Figs. 6.11, 6.12 and 6.13), the bands consisting of one light and one dark coloured member, with an average thickness of 1.3 mm. Similar

rythmi tes have been described from deep lakes in other areas (Tippett,

1963; Ludlani, 1969; Craig, 1972). The first two authors have dealt with

the sedi~entologic~laspects of the rythmi te formation, and concluded that the larrtinations which they examiried were annual. In this case the pale nmkr of the varve couplet, compxec! primarily of clay and a small Figs. 6.11 and 6.32 - 'Frigid finger' core from Twin Lake. The white patch near the poitit is frost formed on the frozen sediment Below - detail showing laminated sediment structure. Fig. 6.13 - Pollen core from Twin Lake, showing lamlnatod structure. 204 an~ountof calcium carbonate, is be1 ieved to represent late spring and summer deposition of eros'onal detritus and algal precipitates , while the darker meinter represetits the deposition of organic material from late summer through the following winter. The material is very similar to the annually laminated sediments of Crawford Lake, Ontario (Byrne and McAndi-ews, 19751, seen by the author in 1971. On the assumption that these were annual varves, the laminae were comted in the field prior to-dissection and battling of the core.

The cour~tswere performed independently 51: se~jmerttsof about. 20 cm. as sh~wnin Table VI.4. The sequence was interrupted betwwn 83.5 and 85.5 cm. and between 86.5 and 87 cm. from the top by unlaminatcd bands, be1 ieved to be Lurbf di tes, as described by Ludlam (1969). If these are not twbid-ites, but merely unlamirrated sediments of sirnildr origin and accum:~Iationrate to the rest, tho actxal age of the basal varve may be somewhat greater than the 718 years indicated by the count. Other inaccuracies may have been introduced by the difficulty experienced in counting the finest of the bands. The values in Table VI .4 thus repre- sent minimum ages, and the basal date may be as much as 50 to 60 years greater than indicated, ;.ri tt~errors tending to acscn~ulatewith increasing depth. The data frw, T&lc Y1.4 were ~sedto construct a sedimentation curve for the cora, as shown in Figure 6.14. As the counting was done in sections, it kas necessary to assume a 1inear interpol ation between points , implying a constant sedimentat ion rate within core segments. This is strictly incorrect, as there are visibie changes in sedimenta- tion rate (varve thicknesc) within sections and the inferred dates Twin Lake -sedimentation rate

Years before 1975

Fig. 6.14 - Twin Lake - Sedimentation curve determined from \:ari..e cc:l;nt.;. corresponclincj to particular depths in Figure 5.8 will contain an addi- tional error term of up to perhaps plus or minus ten years, a1 though the nodes (segment ends) should reflect only the errors noted previously.

TABLE VI.4

Twin Lake: Varve Counts

Cumulative Cumulative Depth Depth Yarves Varves - 0 - lo 10 - 22 22 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 83.5 83.5 - 85.5 85.5 - C6.5 86.5 - 87 87 - 94

A radiocarbon date on the core segment between 45 and 55 cm. yielded a vz'lue uf i,U33 plds or XIIIUS 110 years before 1950 (GaK 5974), substantially greater than the 285 to 385 years indicated by the varve counts, and a sample of surface sediment from shallow water near the core si te yielded a date sf 2,250 p1 us or mi nus 100 years (GaK 5975). Both samples are believed to have been contaminated by the incorporation

~i radiometrica! ly 'dead' carbon -From geolcgical sources, as described by Ogden (1967). Ludlam (1969) repcrted simf 1ar discreparxi es between varve counts and radiocarbon estimates. Consequently, the varve counts have teen used as the sole dating techniqce throughout the fo1 lowing discussion.

(c) Pol l en Representation Pollen data from this core are given as a relative pollen diagram, and as a pollen concentration didgram, in the form of grains per gram of organic sediment. The respective merits of these representation forms were discussed earlier, but the reasons for the choice of the 'grains per gram arganic' representatiwi in this particular case require some explamtiofi. If pollrn concentration data are to be used to interpret vege-

tation history, they must be cmpu ted on the basis of a relatively stable sedimentation rate, or the resulting curves wil I reflect changes in the sedimentation rate rather than chznges in pollen influx. The initial pollen concentration data from Twin Lake, as grains per gram total dry weight, showed strong taxon to taxon correlations , i ndi cati ng relatively large changes in the rate of sediment deposition. It. was suspected that these chdnges in sedimentation rate mrived 1argely from

changes in the rate of mineral clastic influx, and that the rate of deposition of the organic fraction of the sediments was more stable, and would provide a better basis for the pollen concentration calculation. A simple test of this hypothesis is shown in Figure 6.15. Pollen concentration, on a total dry weight basis, is plotted as a function of loss on ignition. The line through the scatter is not a fSttcd regression line, but has been derived under the assumption that

209 both pollen influx an3 olyan-ic probuctiuil~yof the lake have remained constant over time, but that clastic influx has varied. Higher clastic influx will thus produce lower loss on ignition percentages and lower pollen concentration values, resulting in a positive correlation between the two variables. The assumption determines the slope of the line, which is then plotted thrcugh the bivariate sample mean. The assumption pro- duces a reasonable fit to the observed data, and it may be concluded that, in this case, much of the observed variation in sediment deposition rate derives from changes in the clastic influx. Under these conditions, it is preferable to calculate pollen concentrations on the basis of the organic conter,t of the sedimsnts, as shown in Figure 6.17.

B. ------Results and Discussion The pollen and charcozl stratigraphy, as relative and po:len concentrations diagrams, are shown in Figures 6.16 and 6.17, and detailed

Artemisia data i r! Figure 6.18. The percentage and concentration diagrams are broadly similar, and the following comments will apply to both, unless otherwise specified. Total Artemisia values reach minimum or near minimum levels in the decades arognd 1900 (there is one lower value in about 1650 on the percentage diagram) and then increase to relatively high levels, which are, however, exceeded hy uccasionai values at depth. These features are believed to be comparable to the Artemisia ~inimumand the recent Artemisia increase ssen at Richter Marsh, and to represent the relatively open grassland of the early settlement period, and the recent Artemisia f nvasion. As at Richter Marsh, ~inimumvalues are also found in the curve of Gramineae at about this time. In this case the two represent- ations are s~mewhatdifferent, thc: percentage diagrafi placing the

initial decline in Gramineae in about 1890, prior to the increase in

total Artemisia, while the concentration diagram shows the decline after

the Artemisia recovery. Both diagrams indicate some recovery in

Gramineae after about 1930. As at Richter Marsh, the low Gramineae

values are believed to reflect overgrazing. Other features include the

recent increase in Chenopodiaceae, which is believed to reflect the

introduction of Salsola kali in this locality, and ia Populus, which

may relate to the increase in tree cover around the lake, shown in

Figures 5.17 to 5.22 of Chapter V.

A more detailed picture comes from the Artemisia size data of

Figure 6.18. Mean Artemisia pollen sizes reach low values in about

1450, 1650, and 1880 or 1890, and relatively large values occur in about

1800 and the period after about 1940. Division of the pollen concentra-

tion curve into its component size classes reveals minimum values for

the large class in about 1650, and a rather subdued minimum for both the

large and intermediate classes from about 1865 to 1900. As at Richter

Marsh, the recent Artemisia increase appears to be composed of two com- ponents : an initial increase in the intermediate size class (Artemisia triparti ta?) and a subsequent increase in the large class. Again, the

highest recent values for the large size class are exceeded by occasional samples at depth. Although the recent increase in the abundance of

large Artemisia pollen is more dramatic here than at Richter Marsh, perhaps reflecting increased effectiveness of grazing disturbance in increasing establishment success at a site closer to the range edge, the high values from the pre-settlement period again imply that grazing is not a necessary condition for maintenance of an Artemisia tridentata 1971

1950

1900

1800

f700

I600

500

LOO

300

Fig.,6.18 - Twin Lake - Artemisia pollen detail. 1 j population in this area. However, the relatively large values in the

intermediate size class found throughout the pre-settlement period

strongly imply that Artemisia triparti ta, rather than Artemisia

tridentata, was the common shrubby sagebrush until relatively recent

times. This conclusion is in accord with Dawson's (1876) observation

of Artemisi a tripartita (Artemisia trifida) at 1ower elevations in the

Similkameen Valley and at Osoyoos, and raises the possibility that the

'sagebrush invasion' recorded by Camsell at White Lake in 1912 was in

fact the expansion of the Artemisia tripartita population implied by

the intermediate size class curve at that time.

The three mechanisms which may be responsible for these changes,

fire, climate and grazing, remain difficult to separate. The low values

for mean pollen size and the paucity of large pollen in about 1650 may

reflect 'Little Ice Age' cooling at this time (Bray, 1971), and the low

values of the late nineteenth century may have a similar cause, but both

periods also show relatively high charcoal values, and no clear distinc-

tion is possible at this time. Similarly, although it is tempting to

assign all of the recent Artemisia increase to the effects of grazing

disturbance, this is also a period in which fire frequency is known to

have decreased, and no clear separation of the relative importance of

these changes is yet possible. Of the three factors, only fire history

is susceptible of direct quantitative assessment and correlation with

the vegetation record, and this task is undertaken in the following

section. C. The Charcoal Record

It was established earlier that much of the variation in sedi- mentation rate at Twin Lake has been due to changes in the rate of clastic influx, resulting in changes in the percentage of organic matter in the sediments (loss on ignition) and in the pollen concentration. In addition, the loss on ignition values appear to correlate with the abun- dance of charcoal in the sediments, as shown in Figure 6.19. After explaining the derivation of this correlation, the foll owing section describes how these relationships may be used to further clarify the available charcoal record, by subdivision into a component largely derived from forest fires, and a component largely derived from grass- land fire. The index of grassland fire occurrence which results is then compared with the pol 1en record by means of a mu1 tipl e correlation analysis. This procedure serves to test whether the index does indeed correlate with grassland taxa as expected, and may serve to elucidate the effect of fire on the grassland ecosystem. Figure 6.19 shows charcoal abundance, as a percentage of the pollen sum, plotted as a function of the loss on ignition. Because loss on ignition decreases with increased cl asti c influx, the negative corre- - lation obtained is approximately equivalent to a positive correlation between charcoal and clastic influx. It is believed that the correlation results from the influx of erosional detritus to the lake after the slopes of the watershed are burned and the s tabi 1i zi ng vegetation removed. The upper five sample points from the period after about 1940 appear as distinct outliers from this general relationship, and may reflect other erosion sources, such as cottage building along the lake.

In order to avoid the effects of these and other possible human distur- bances, the regress ion analysis was restricted to the pre- 1860 peri cd, although only the post-1940 points appear to departsignificantly from the general r-ela tionship. Because most of the slopes of the watershed are presently forested, including those which are steepest and most erosion prone, it is prclbable -that most of the erosional detritus derives from forested slopes, and therefore tends to index the occurrence of forest, rather than grassland fire. This inpl ies that the general relationship shown in Figure 6.19 is actually between charcoal derived from forest fires and loss on ignition of the sediments. If this is so, it may be hypoth- esi zed that the remaining charcsai variance-- Lhe residuals fron; this relationship--rzpresents charcoal derived from other sources, including forest fires on other watersheds, and grassland fire. If the bulk of the charcoal comes from iocal sources, these residuals should tend to index local gr3sslacd fire occurrence. Thew residuals are plotted stratigraphical ly in Figure 6.20. The fluctuations about the zero mean include a long run of positive deviations (hish grass ffre itldex) from about 1820 to 1920, and a series of negative residuals after 1920. Although the post-1940 points may be exaggerated by othw form; of disturbance, the general decline in the index after 1920 is similar to that for grassland fire presented in Chapter V. Two forms of validation of this index have been attempted. If the residcais are merely random sampling errors, unrelated to any real events on the :anciscape, it would be expected that the deviatiom wouid Bate - 1940

Chercoal Residuals Fig. 6.20 - Twin Lake - Residuals from regression of charcoal on 105s ~riigt~ition, as an index of yrasslsnd fire occurrence. 219 show no temporal patwrn, but if they are related to real events with some degree of temporal continhity or persistence they may show a pattern of sequentia; runs of positive and negative dev.iations. This may be tested with a runs test (Hays, 1963) in which the number of runs of positive and negative deviations is compared to an expected number generated under an assumption of random fluctuations. In this case the actaal nun~ber of runs is fourteen, and the expected number in a series of this length is twenty-five. The calculation yields a Z score (normal approximtion) of 3.21, implying significance at the 1 percent level. It may be concluded that the residuals are not randomly distributed in time, an3 probably represent the occurrence of some real phenozenon not accounted for by the ch6rcoal--loss on ignition regression.

A more po~~erfultest comes from a compariso~of the index with the pollen record. If this is an index of grassland fire, any correla- tions between the index and the various taxa of the pollen record should be with taxa frm the grassland rather than from the forest. The analysis was performed by stepwise ~lultiple correlation, using the percentage

cha.rcoal values as the dependent variable and the Twin Lake pol'1 I en con- centration values, loss on ign~tior,, mean Artemisia pollen size, and the concentrations of tho three Artemisia s-ize fractions as indeperident variables. li~~analysis was perforrxd twice; once for the ~re-1860 period, and once for the entire core. The pattern of simple correlations with charcoal is shown in Figure 6.21. There is a tendency for the arboreal taxa to show negative correlations with the uncorrected charcoal data, and for non-arboreal taxa , ir.cs udi ng Granii neae and saverai grass1 and weeds, to shaw tive Pic pa Ts cga Cupressaceae Abies Ps eudo!sr~ga Pin u s Be tiria A inus Salix Popu!us Gramlneae Art ernisia other Compositae Chenopodiaceae Ambrosia Selaginella Trilete Cyperaceae MyriopAy!l um /'otornoycton Sambucus Pursk.43 inem pollen siz~ - small pollon intermediate large polten loss on ignition

-7- - .4

Fig. 6.21 - Twin Lake - Simple correlations between charcoal percentage and pol 1en concentrations for selected taxa. I. all data 11. prz-1860 Vertical lines mark 5% values of r. correlations. As expected, both loss on ignition and mean ---Artemisia pollen size show strong negative correlations.

The mu1 tiple correlation results are shown in Tables VI.5 and

VL.6. Loss on ignstion is the first variable en~ployedin the analysis, and the variavce remaining at the end of this step is consonant with the grassland fire index discussed above. The remaining variance is

'explained' by mean -Artemrsia pollen size in both the pre-1860 and the entire data versions, followed by Chenopodiaceae in the full data csse, and by --.A.Ambrosia and Sambucus in the ?re-1260 case. A17 are tam of the grassland or foxst border, No forest taxa appear in the analysis, pre- sumably because their partial corwlations with the charcoal series fell to low levels with the removal of the variance associated with the loss on ignition estimates. A13 cf thz variables included are significant at the 1 percent level or better. However, the inclusion of Chenopodiaceae in the full data made! may be spurious, for much of the recent increase in this taxori appears to relate to the recent invasion by Salsola kali , and my not be directly related to changes in the fire regime. In general , however, it may be conc! uded that the residual variance from the charcoal--loss on igr,ition re~ressionis best predicted by the pollen record of grassland taxa, and that those residuals do tend to index grassland fire.

This analysis also provides some insight into the components of the mean ----Artemisia pollen size statistic. Table VI.7 shows the pattern of simple correlations between mean --Artemf sia pollen size, and the pollen concentration val ues for the three compcnent size fractions. TABLE VI.5

Multiple Regression--Charcoal Content as a Function of Selected Parameters, Twi n Lake, A1 1 Samples

Step No. Variable -R -R~ 1 Loss on Ignition .604 .365

2 Mean Artemisia Size .783 .613

3 Chenopodiaceae -8277 .677

Constant

TABLE VI.6

Mu1 tipl e Regression--Charcoal Content as a Function of Sel ected Parameters, Twi n Lake, pre-1860

Step No. Variable R

1 Loss on Igniti on .837

2 Mean Arterni sia Size .862

3 Ambrosi a - .889

4 Sarnbucus .904

Constant

N = 35

** Significant at the 1% level. TABLE VI .7

Correlations Between Mean Artemisia Pollen Size and Abundance of Artemi sia mxzeFractions

Pol 1en Concentration Correlation With Mean of Artemisia Pollen Size ** Small Grains - .572 Intermediate Grains .097 Large Grains .663** ** Significant at the 1%level.

It is evident that the mean Artemisia- pollen size statistic reflects the changing abundance of both the large pollen fraction and

the small pollen fraction, and is not a simple index of Artenlisia- tridentata abundance. Figure 6.21 shows that these fractions have different relationships with the charcoal record: the large fraction showing the expected negative correlation, and the small fraction show- ing a degree of positive correlation. There is evidence, then, that at least two independent populations contribute to the total Artemisia count, and that the population which corresponds with the small pollen fraction,

probably Artemisia frigida ir, large measure, increases its representa- tion in the local pollen rain after fire. This increase in pollen representation may ref 1ect densi ty i ncreases , or i ncreased fl ower pro- duction, or both. This increased production of small Artemisia pollen

' following fire probably accounts for the relatively weak minimum of total Artemisia pollen during the early settlement period at this site. D. -Summary The core at Twin Lake presents an overall similarity of pattern to the corresponding period at Richter Marsh. The early settlement period in both cases is marked by a reduction in the abundance of total --Artemisia pollen, and a reduction of the mean size of the Artemisia grains, indf cating lower populations of Artemisia-- tridentata. Subse- quently, both cores show evidence of a period of overgrazing, as a marked drop in the abundance of Gramineae pollen, followed by a period of recovery. In both cases the period of overgrazing coincides roughly with the beginning of an --Artemisia increase which may have occurred as two successions! s tages--an early increase in Artemisia triparti ta and a later increase in Artemisia tridentata. As at Richter Marsh the

----Arteinisia lninirnum of the early settlement period is preceded by a pericd of greater Artemi sia ab~ndance,in which , however, species other than Artemisia Xidentata appear to predominate. The core from Twin Lake contains an abundance of fine charcoal, and it is again possible to demonstrate a statistical relationship between charcoal abundance and indices of the size and species composi- tion of the ---Artemisia population. Grassland fire appears to have been an important ecological factor at this site throughout the period of record. There is evidence of a nargina7 increase in grassland fire frequency at this site during the latter half or two-thirds of the nine- teenth century, and of a decline after about 1920. The principal differences between this core and the one from Richter Marsh relate to the rnagni tude of the apparent changes in the Artemis'a population. In caiyarison to Richter Yarsh the ---Artemisia minimum at Twin Lake is relatively subdued, perhaps because a larger proportion of the total Artemisia pollen received at this site comes from Lrtemisia frig.ids. and Artemisia tripartita which are more tolerant of, or perhaps favoured by, fire. The recent --Artemisia recovery at Twin Lake is much more dramatic than at Richter Marsh, and appears to raise the modern population level above the average, if not the maximum, level found in pre-settlement times. The differences may relate to differevces of situation. Whereas Richter Marsh is we1 1 within the bioclimatic range limits of Artemisia mdentata in this area, Twin Lake lies close to the apparent range edge where grazing disturbance or alteration of the fire regime may be relatively more effective in altering the population size.

VI. Fossil Pollen Spectra 111:

-Mahoney ---- -' Lake A. Site arid-- Eethod (a) -Location and Sampling

Mahoney Lake (49 degrees, 17 minutes N, 219 degrees, 34 minutes W) (Fig. 6.1) was chosen as the third member of the environmental transect. Although the lake's elevation, at 487 m., is below that of Twin Lake, the situation appebrs relatively more mesic, and the lake is presently sur- rounded by forest of Pinus ponderosa and -Pseudotsuga --- menziesii var glauca. The nearest grassland area, Meyer Flat, has an annual water deficit lower than that at Twin Lake (Davis, personal communication) and is presently free of Artemisia tridentata, although a few plants do occur near the lake. The lake has an area of about 0.4 square km., about the same as Twin Lake, but. a drainage basin of only 3.63 square km. The lake is spring fed, and receipts of overland flew appear to be very 1imited. A core of 54 cm.was taken from the centre of the lake in 14 m.

of water, using the freezing sampler previously described. The core was composed of black to reddish-black algal mud, and calcium carbonate.

In some sections the alternation of these two components produced a

banded pattern, which was however quite unlike that found at Twin Lake,

the bands being coarse and discontinuous, with poorly defined zones of

contact. The origin of this patterning is unknown, but the irregularity

of the laminae suggests that they are not the product of an annual cycle

of sedimentation, or that they have been badly distorted. The core was

sectioned in 2 cm. segments and retained for analysis.

(b) Dating

A sample from the 50 cm. level yielded a radiocarbon date of

3040 plus or minus 140 years before 1950 (GaK 5688), while a sample of

surface mud provided a date of 940 plus or minus 230 years (GaK 5973).

The difference between these two values provides an estimate of 2100

years for the age of the basal sample.

This figure must be doubted. It represents a very slow rate of

sediment accumulation, of perhaps a metre in 5,000 years making some

allowance for compaction- at depth. This is only about one sixth of the

rate recorded at Twin Lake. In contrast, the concentration of pollen

per gram of sediment is rather similar at the two sites, particularly

for such regional taxa as Tsuga and Abies, suggesting either similar i 1 sedimentation rates, or that Mahoney Lake is a much less efficient pollen trap. It would appear that the radiocarbon dates have been badly dis-

torted by the assimilation of geological carbon by the aquatic vegetation

of the lake, as appears to have occurred at Twin Lake. If sedimentation 227

rates at Mahoney Lake are only slightly lotier than those at Twin Lake,

as indicated by comparison of the pollen concentrations at the two sites,

the time span represented by the core would be 200 to 300 years, rather E than the 2000 year estimate provided by the radiocarbon analysis. This concl usian is supported by pol len stratigraphic comparisons with the

Twin Lake core (see below), which indicate a basal date of approx5mately

1650 A.D. It is on this time scale that the following interpretation

is based.

B. Results and Discussion

Relative and pollen concentration diagrams for Mahoney Lake are k k t shown in Figures 6.22 and 5.23. The relatively stable loss on ignition

curve (Fig. 6.26) and the absence of a statistically significant corre- s k lation between loss on ignition and charcoal abundance, or between loss . h on ignitfon and pollen concentration (Figs. 6.24 and 6.25) imply a F L % L relatively stable rate of clastic influx to the site, and pollen con- B h centrations have been given as grains per gram total dry weight. i Individual pollen taxa show little systematic variation at this s. p site; the impression is one of relatively stable vegetation in the vicinity of the lake over the period of record. The most notable

exception is seen in the curve for Populus, which shows a sharp increase

above 30 cm. Total Artemisia pcllen redches m'nimurn values at 15 cm.,

but the total variation in the curve is subdued, and there is little

evidence of a recent increase in total Artemisia. Similarly, the curve

of Gramineae is relatively stable throughout the period of record,

falling only in the uppermost sample. There is little evidence here of

a severe early perfod of overgrazing, such as was found at Twin Lake and at Richter Marsh.

232

More detailed krtemisia data, shown in Figure 6.26, reveal a more familiar pattern. Mean Artemisia pollen size shows a gradual rise from low values near the bottom of the core to a maximum at 25 cm., low values frox 25 through 15 cm., and a modest increase from 13 cm. to the surface. The pattern is similar to that found in the upper half of the Twin iake core. Similar also is the curve for large Arteniisia pollen concentration, which rises from low values at the bottom of the core to a max'mux at 25 cm., declines through 15 cm., and rises towards the surface. It was on the basis of these similarities that the 300 year basal age for the bottom of the core was inferred. The 'sagebrush minimum' is spparently present between 21 and 15 cm. The smal ler pollen classes show no evidence of low values in the

21 to 15 cm. seynlent. The abundance of the sriallest class of -Rrtemisia pollen reaches a distinct maximum at 21 cm. and declines thro~gh15 cm., maintaining relatively low values to the toy of the core. The smaller pollen classes show little similarity of pattern with the large class, and because, as at Twin Lake, they form the greatest part of the total

---Artemisia count, the sage to grass ratio does not reflect the fluctua- tions in ----Arternisia --tridentata implied by the ~riean size, and class abundance cwdes. Although the size class data provide evidence of a recent

--Artemi -- si a- tri- dentata-- i ncrease, recent val ues remai n 1ower than those achieved in the inferred ~re-settlementperiod. It is again difficult to attribute the recent increase to the effects of overgrazi~g,for there is evidence of high -Arternisia tridentata- index values from the period before cattle were introduced, and there is 1i ttle evidence of overgrazing at any former period in the vicir~ityof this site, as shown by the curve for Grmineae.

C. The Charcoal----- Record There is again an abi!nddnce of fine charcoal throughout the core. There -is a minor peak at the bottom, which may correlate with a similar peak at about 45 cm. at Twiq Lake, a major rise between 23 and 15 cm., and a subsequent decline. The rise between 23 and 15 cm. corresponds to the apparent 'sagebrush minimum' and may be tentatively identified with the early settlement period.

Regression of mean --- Artemi sia pol 1en size, and the concentration of the large -----Artemisia polien fraction cn charcoal abundance, as percen- tages of the pollen sum (Figs. 6.27 and 0.28) yield significant negative correlation coefficients (Pearson's) of -.5167 and -.5905, respectively, both significant at the 1%level. It would appear that a substantial portion of the charcoal arriving at this site has heen derived from grassland fire, for forest fires would be unlikely to affect the Artewisia population, in spite of the fact that the immediate surround- ings of the lake are now largely wooded. The effect cf thzse fires appears ts have b~ent? reduce ter~porarilythe abundance of Artemisia tridentati

Although the dating of the Mahoney Lake core must remain tenta- tive, it does serve to demonstrate that the strati~raphicchanges observed for the various ---Arte~ilisia indices, and for the charcoal counts, are regional rather than merely local in nature, as is the re?alionship between these indices of ----Artemisia tridentzta abundant? and ihe index of fire freql~?i~cyprovided by the charcozl record. The record &tthis 5ite implies substantial Artemisia tridentata populations in the pre- settlement period, low population levels du:-ins a presumed early settie- went phase, and a msdest increase during recent times. -9Ine correlations obtained between charcoal and the Arternisia tridentata i cdi ces irnply that fire has been a major determinant of the abundance cf the species throuyhout the period of record.

VII. Summary ad ftisc~ission

In spite of the range of habitats from which these cores are derived, many common features may be recognized. A1 1 shm 501x2 cviderxe of a recent increase in the abundar~ceof Art~misiztridcnta~3, as a!: increase in total Arternisia pollen, as an increase in mean -Artemisia ------polle~isize, and as an increase in the large Artemisia pollen fk-action. This observation accords well with the repeated observatio~~sof a sage- brush invasion of this and other areas in the late nineteenth and early twentieth centuries . In all cases, this increase succeeds a period of low Arte~isia

--tridentath -- abunds nce, as i ndi cated by the various pol 1en i ndi ces . Thi s is !-!I:? ocly period of the recent past which corresponds to the descriptions of an open, brush-free grass1 and common in the nineteenth century accounts. This per-iod of 1ow -Ai3temi- --- sia -iri- deniata -- abu!~aance is bounded below by another period in which the species appears to have been more common.

The dating of this recent -Arte+,iisia------mi nimurn is tentative, and may not be entirely synchronous at a11 sites. At Richter Marsh, on the bas's of stratigraphic inferences, it appears tc be at least partly post-settlement., while at Twin Lake the vave chro:~ology indicates a period fron; sbout 1865 to 1900, Thus, wh'ile the polien data confirm the impression conveyed by the historicsl sources of recent invasion of previously apen grassland, they also indicate that Artemisia- tridentata populations in the period before European seClement were i n general only marcjinally smaller than, arid occasionally exceeded, those of the present day. In comparison to the cor~ditionsof the late niceteenth century, the recent irkcrease is larcjc and drmatic; in comparison with the longer time period representgd by the pollen cores it is much less so, for it becomes but sne of 5 serfes of fluctuatiorls of similar may ni tude . This pwint may be emphasized by considering the various Artemisia-

?ndices--total --Artcmisia pollen, meari pollen size, and the sage to grass ratio--as random stochastic variables. The dctual pollen samples are t+.. r US. random samples drawn from the index popul aticn wer time. Under conditsons of dynamic equilibrium the frequency distributions of these indices might be expected to have approximately norm31 form, with a well defined rccan, and a range of encompassing variation. Any alteration of the equilibl-iurn shaaid result in a shift f r; tht? position of the mean, and in sample pcints which fall beyond the earlier range ci varia.tion. Histogranis of these indices fcr the three s

-.---Astemisia percentage, and 2.23 for the sage to grass ratio. These data provide little evidence of a fundamental, qualitative change in the ec,olsyical status of ----Arternisia ----tridentata in this area in recent times.

Instead, ths changes which have occurred appear to be ~erelyqtdantitative variations within the context of a single equi i ibrium state, whose dimensions cai? be adquateiy recognized and sampled only over a time peri~dof several cent.uries . The {{at?. imply cimges in the abundance of the other species of

-RrtmisSa - in the zrea as ge11. The small and intermediate pollen Richter Marsh I *

Artcmisia Polien Percentage

Twin Lake 1

Arternisia Pollen Percentage

Mahoney Lakc

. Artemisia Pollen Percentage

Fig. 6.30 - Histograms of total ----Arteniisia percentage. The numbers on the Twin Lake diagram give approximate date. Richter Marsh

- Twin Lake

Sage/Grass Rat io

Mahoney Lake

Sage/Grass Rotio ~jg.6.31 - Histograms nf sage to grass ratio. Nodern values as -indi ca tzd . Frequency Frequency

O..NWC~VICn classes appear to have been reiztively more abutxiant in pre-settlement times than they are at the present. Although no exact correspondence bi?twee~particular -Artmisia species and the srnaller pcllen size classes can be ciaimcd, the data imply that Artemisja fr%ida- and A-rternisia triparti ta wtlre more abundant in ~re-settl ement times than they are today, a~dtend to confirm the impression conveyed by the historical sowces rhat these spccfes were the principal representatives of the genu ---Arzemisia -.-- during the early settlement period. The evidence sug- gests that the recent Artemisia- increase was composed of two successional stages, with the intermediate pollen class, perhaps represent n g

--Arternisia --- --'ir-iyarti ta, increasing first, to be si~cceededafter about 1930 at Twin Lake by the large pollen class, probably representing Artemisia ---tri tlmtatii. The intermediate size class appears also to have partici - pstcd in the recent Artemisia minimum.

Of the three factors whfch are likely to have caused these changes--climate, fire and grazing--only the effects of fire can be conclusively demonstrated. Fire appears to have been a major factor in determining absolute and relative population sizes w: thi n the Artemisia species present over the period of record. Fire frequency appears to have increased during the early settlement period, as shown by the char- coal record, and to have declined after 1900 or 1920, as shown by both charcoal and documentary sources, and these changes probably account for a substantial part of bcth the recent Artemisia minimum and the subsequent ----Arteriiisia increase. The roles of the other factors are less clear. Climatic effects may be suspected, certainly in the large changes which are shown in the earlier part of the Richter Marsh core, and perhaps in the 1650-1750 (Little Ice Age) spectra from Twin and Mahoney Lakes. Secular climatic variation may also have influenced the cGurse of more recent population changes, but the degree of this i rrfl uence appears to be small , and to have been overshadowed by changes in the fire regime. The pollen data appear to confirm the earlier finding that graz- ing d.isttrrbance is r,ot a necessary condition for the maitltenance of Artercisia -----tridentata populations in ttlis area, but the degree to which such disturbance may have influenced the pattern or extent of the recent increase is less clear. In general, the extent of this influence appears to have been small, for only at Twin Lake is there clear evidence that

modern Artemisia -tridentata - population levels exceed the average levels of the pre-settlement period, and much of this change can be accounted

for in term of changes in the fire regime. Direct grazing pressure may have beep more important in reducing Artemisia frigida populations , and sheep herding in the nineteenth century may have had a similar effect on

---Artemisia -t~iparti --ta (Laycock, 1967). Grazing induced changes in these populations would certainly tend to affect the mean pollen size statistic,

independent of fire induced changes, and may have had some real effect on

---Arteaisia tridentata populztisns by a1 teri ng the competf tive environment. Al ternatively, tawever, the recent decline in the ma1 1 pollen types may

reflect only competitive displ acement of these species by Artelnisia

tridentata in an environ~entin which fire has becoine infrequent. This latter hypothesis is perhaps the Rore probable, for low values of the small pollen populations also appear to have occurred in pre-settlement

tirnes , before yrazf ng pressure becam extreme. CHAPTER VII

SUMMARY AND CONCLUSIONS

The ecological picture which emerges from these studies is cne of ccnlp?cx :: ~~~eraction..+ between a species poprr!ation and its biotic and abiotic env ?;ror~ment. These interactions operate at a variety of scales in time and space, some of which are more susceptible uf investigation than others, but of the many factors which exert some degree of control on the population, only a few seem to be significant over long periods and large areas.

It is evident that -----Artemisis -tridentata is a long standing component of the driest parts of the natural grasslands of the southern interiar of British Colunbia. it is capable of maintaining large popu- lhiions attile present time, and was able to do so under most of the condi tions which existed in this area during the Holocene. Present-day populations and population fluctuations are not simply a result of ~vergrazingdisturbance during the past century, and in most of the area grazing disturbance fs neither a sufficient nor a necessary condi- tion of reproductive success in this species.

Recruitment success is dependent, in part, on the occurrence of suitab1 e we2 ther conditions , inc1 udi ng mi 1d winters , summers with adequate moisture for seed1 ing grwth, relatively warm spr-ing and cool autun?!~corditions , atid autumns with adequate soil moisture but 1 i ttle rain. All of thsse factors appear to be link9d to processes of seed and seed1 i ng development. Recrui tment fai 1 ure due to competition appears to be related to the degree of grass cover and the availability of bare mineral soi 1 germination sites . Mi crosi te avai 1 abi 1i ty may increase as a result of prol~ngeddrought or as a result of grazing dfsturbance. Intra-specific competition may also limit recruitment success, apparently through allelopathic suppression of seedlings by the establ ished population, but this mechariistn appears to be primari 1y of short-term and local importance. Adult n~ortillitypatterns appear to be relatively stable, similar to those described by Hett and Loucks (1976) for tree populations, but fire may cause catastrophf c adul t mortality resulting in a successional sequence in which other species of Artemisia may play a prominent sera1 role. These factors function in both time and space, and may be collectively responsible for much of the existing density and distri bu- tion patterns of the species, and for many of the past changes in those patterns. A1 though individual factors may be capable of completely suppress1ng the species in particular areas at parti cul ai- times, popu- lation control by several factors which may be additive or interactive appears to be more common. Such mu1 tivariate control must make hazardous any simple explanations of present or past population patterns based OK single factor hypotheses.

Despite the difficultf es imposed by mu1 tivari ate population contwls, some explanzto~ydescription of the history of the species in this area is possible. Prior to European settlement the Artemisia

.----tridentata peps1 fitinn was probably subject to control by c! imatic factors and fire frequency. Although fire effects are detectable

throughout the Richter Marsh core, the major population fluctuations

prior to the last century appear to have been governed primarily by

I climatic changes, with fire imposing only re1atively minor, short-term

effects. This is particularly true of the major population expansion

of zone 11, which has been identified with generally warmer or 'Hypsi-

thermal' temperature conditions at that time. In this case the term

'warmer' may include such factors as milder winters, warmer springs, or

drier summers, any one of which might be expected to lead to some

population expansion. Subsequent to this period, the population seems

to have declined. Because there is little evidence of a marked increase

in fire frequency until recent times, it is probable that the decline

was primarily of climatic origin. In detail, however, the separation

of climatic and fire effects is difficult or impossible. Although the

low Artemisia tridentata population of about 1650 to 1700, inferred from

the Twin Lake and Mahoney Lake cores correlates well with the conven-

tional dates for the most severe period of the Little Ice Age, it is

accompanied by a prominent charcoal peak, and may be partly or wholly

a result of fire. Grassland fire frequency may itself be partly

dependent on climatic controls, as is the case with forest fire, but

the nature of such controls, if they exist, is unknown.

During the first half of the nineteenth century the lower valleys

of the study area appear to have supported Agropyron spicatum grassland

mixed with, or perhaps dominated by, a shrub community in which Artemisia

tridentata was a prominent member. Artemisia tripartita and Artemisia

frigida were apparently more common than they are today, perhaps reflecting a slightly cooler climate, but probably beczuse recurrent fires permi tted only 1ocal and ephemeral domi nance by Arten~isi a tridcntata and maintained much of the landscape as a niosaic of succes- si ona 1 stages . The advent of Ecropean settlement altered the suite of existing envi rorrmental controls and led to corresponding changes in the population equi 1i br-i um. Both the existing documentary records and the charcoal record irom the pollen cores indicate an increase in fire frequency during the early settlement period. The fire increase appears to stem from the addition of intentional and unintentional burning by prospectors and ranchers to the continuing pre-settlement ignition sources of light- ni n~ and Native burning . Under a regime of greater fire frequency the Arternisiz tridentata, and perhaps also the Artemisia- triparti ta populations declined dramati- cally. The ----Artemisia frigida- population appears to have remained roughly constant, or perhaps increased slightly, judging by the curves of small krtemisia pollen at the three sites. The pollen record frcm this period records low values of total Artemisia pollen, mean Artemisia pollen size, and the sage to grass ratio; values which imply that the Artemisia

----tridcntata population shrank to levels aq low as or lower than any experiencd fur at least several centuries before. The decline is detectable in all of the pollen cores examined, and appears to have been of regional extent.

Other changes at this time appear to have resulted from the introduction of domestic 1i vestock. The vul nerabi 1i ty of the native bunchgrass was evident by the early 1870's and by the 1880's the damage 250 was sufficiently great to be recorded as a marked decline in the abun- dance of Graixineae pollen. There is evidence as well of a decline in

-----Artem-isia -frifida, - perhaps as a result of grazing pressure. The sax contemporary accounts which first record evidence of overgrazing also record an increase in Artemisia frigida and at least one fom of shrubby sagebrush--8rtemisia-- triparti---- ta or -Artemicia-- -- triden-- tata, In t!~rase of Frtemisia -friqida, the rapidity with which it is said to have replaced b~nck~grass,and the lack of evidence for a dramatic increase in the pollen record suggest that the reports reflect an increase in the visibility of the species, due to a reduction in grass cover, rather than any great increase in density. In the case of the shrubby

-Artemisia species, the only re1 iable contemporary taxonomic data, and the pollen record indicate that ---Arteriiisia -tri~artita was the first to take advantage of the altered competitive environment. The reasons for this may lie in the lzrger initial population and more common seed sources for this species at the time, or in the continuing high fire frequency which is imp1 jed by the charcoal record.

The Artemisia -tridentata - increase ap~earsto date from perhaps 1890 or 1900 in the Cawston area, but is not detectable in the pollen record from Twin Lake until about 1930. The age structure sample records major establishment periods in the decades after about 1925 and again after 1955, but includes at least one plant from before 1900. The pollen data indicate that this increase began during or irnmediateiy followincj th2 period of severe overgrazing rzcorded by the low Gra~ineae values, bx the occasional high Arternisia tt--identata index values recorded fro;;? the pre-settlerwnt period, and the decline in fire frequeqcy after about 1920 indicated by both docun~entaryand charcoal records strongly suggest that changes in the fire regime, rather than grazjng disturbance, were the primary cause. The actual timing of ar.y local incwdse was probably conditioned by the degree of grazing dis-

turbance, we?tb.er conditions, and the avai 1zbi l i ty of seed sources, but it is unlikely that any significant population expansion could have occurred i n an envi ronment domi na ted by recurre7 '. f i re, however favour- able other conditions might have been.

Presmt memi si a tridenta td popill ations appear to be above the mean, but ncrt above the maximum 1eve:s recorded in the pollen record for the pre-settlement period. The recent increase is most dramatic at Twin Lake, which appears to be close to the present climatic range edge and nay be more sensitive to changes ir, the amount of grazing disturbance or fire frequency than other areas sampled. Pol len evidence indicates that

the populations of the other -Artemisia - -- species have recently declined, perhaps due to grazing pressure in the case of Artemisia frigida, or as a result of increasing cornpeti tion froin &emisia tridentata. This reconstruction differs substanti a1 ly from the eariier accounts of Wedver and Clements (1938) and others. The open, brush-free grasslands widely reported in the early literature appear to have been anomalous, the product of an intensified fire regin:e in the decades after the first Europea~contact. Although it may never be possible to

I obtain a detailed picture of the condi tion of these grass1 ands prior to I European settlement, the available data imply a substantial brush cover, often approaching that of the present day. The changes which took place

ir, the late 13-ir~eteenihat76 early i;wc!+t-ietfi cenf,uries and on which the 252 hypothesis cf a grazing disclimax were based, were real but the extent and signiff cawe of the changes have been seriously exaggerated. This error sleirs, in large measure, from the assumption that the earl Zest historical rec:lrds documented the typical condition of the natural vegctatrun. Such an assmption may often be unfounded, and should be subjected tc critical tests whenever possible.

If, in "Le absence 3f fire, Artevisia tridentata forms an important c~mpon2ntof the natural grasslands in this area, managemint schenres wh:'ch ~"Ltcmptto cmtrol the species by reduced grazing pressure, and a return to more 'natural' conditions ?re unlikely to succeed unless they include ffre or some other form of periodic weeding. The use sf fire as a range management tool in this area deserves further study. Even with the historical pa-spective which is now available, it is impossible to make confident predictions about the future course of popul ation change in thi s species. With continued fire suppressi on, the populatjon should continue to approach upper density limits defined by intra-speci ffc comp?tition, and range 1irni ts determined primarily by climate. Act~aldensities may frequently lie below such 1imi ts, after extended periods of 1irni ted recruitment due to unfavourable weather. It remains cncel-tair; whether any absolute climat-ic range limits have yet been reached during the re lativeiy short i nlerval of fire suppression. Fire suppression over extended periods is unprecedented and the his tori ca1 record provides little basis for prediction. It may be that many stands of Arteniisia------tridentata in this area are at densities greater than can be sustained cver long pzriods, and will in future decline in response to ccntinued acciltwlati~nof grass and -----Artemisia fitter. Extrapolation cf these results to other areas or other species shouid be undertaksr only in the most ge~era'lsense. Certainly, the limiting climatic factors identified in this study are unlikely to reta.19 their importance at the southern or arid margins of the species range, a:~dare wobahly replaced by an entirely different set of con- trols. In areas further removed from the range edge, the importance of cl inat?c zonT.rols may decrezse, as the frequsncy of conditions beyond the species to1 erance 1imi ts decl i nes . In such areas, competi tive factors nidy b? ~or2irnporta~t. Although fire may be relatively more important Rear the species range edge, where reinvasion is slow, it has the potential to have altered ----Artemisia tridentata densities throughout the range in ~hepast. High nineteenth century fire frequencies may account for the apparent. 'sagebrush invasion' in other areas as well. A sirqle case study provides only a slim basis for generalization ahout other species populations, b~ta few inferences may be appropriate. Thew is no reason to believe that the suite of environmental ccntrols identified in the case of Artemisia tridentata is unusually complex, and the complexity of these controls should warn against simplistic, single factor explanztiom of population size Dr distribution. Because such papu1atior.s may retain the imprint of historical events for relatively long periods, the assumption of environment - population equi librim must often be true only in the most general sense, and short-term observations may provi'de ntisleading results. The techniques of long-term observation which have beer: used in this study may lose in detai 1 m~chof what they ~aiuin scope, but both the pollen and age structure txethods appear czpabie of providing insights into populat5orl history and population ecology which are obtainable in no other way. BIRLIOGRAPHY

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Peck, R. M. (1974), A Comparison of Four Absolute Pollen Techniques, New Phy to1- ogi s t, 73, 567-587.

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Ycung, J. A., 2. A. Evans, and J. Major (1972), Alien Plants in the Great Gasin, Journal of Range Management, 25, 194-201. APPENDIX I

Derivation of Pollen Deposition Rates

--Fur= Of the available methods for calculating fndices of the abund- ance of particular pollen taxa within depositional sequences, only those which yield estimittes of the pollen deposition rate, in grains per unit area per yesr, ?re theoretically free of the bias introduced by changes in the abundance of other taxa, in the case of percentage calc~~lations, or by changes in the rate of sediment deposi tion, in the case of the various pollen concentration techniques. For this reason, it is desir- able, where possi ble, to quantify pol 1en abundance as deposi tion rates.

The basic requirement of such a caiculation is an accurate estimate of the rate of sediment accumulation within the sample core. Such esti1nat.e~ appeared to be available from the varve counts at Twin Lake, and an attempt was made to transform the existing pcllen concentration esti- mates to es tirrlates of pol 1en deposition rate.

Method

The dei-ivation of pol 1en concentration estimates was out1 ined in

Cka~tcrVI, In order to convert pollen concentrations, by weight, to pol 1en depnsi tion rates, two further parameters are necessary.

(I) Pol 1en concentrations mus t be expressed in volumetric terms, for sedirnenta.tion rates are obtained as depth increments over unit areas; i .e. as volume increnients. In calculating the concentrations, the nccesszt-y vol umetric measurements nay be made directly, as estimates of the volume rather than the weight of the original sample, or pollen concentrations by weight may be converted using estimates of the density of the sediment.

(2) If pollen concentrations as grains per unit volume are known, and the sedimentation rate is known, the pollen deposition rate may be obtained by multiplying the concentration by the sedimetitation rate. Thus, a concentration of 100,000 grains per cubic centimetre, and a swi:neniatiun rate of 3.1 cm. per year, would represent a pollen deposition rate of 10,000 grains per square centimetre per year.

-Method for Obtaining Volume Estimates A first problem is to obtain accurate measurements of small (0.5 to 1.0 cc. ) volumes of wet sediment. Two methods have been proposed. Sedircent volumes may be measured by displacement in a graduated vessel

(Pennington, WZ), or by the use cf a calibrated spoon (Maher, 1972). ' Mahe?. claims that tho spoon technique yields estimates with an error raDge of plus or minus 2.5 percent. I have tried both methods and have been unable to even approach such precision. A major problem in both cases is the elimination of bubbles within fibrous or flocculated xaterials. Sediment volumes in this study were calculated using the initial weight of the wet sediment sample, the proportions of the sample composed of water, organic material (as loss on ignition) and clastic ~aterials,and assumed densities for each of ti~esecomponents. The acsmed densities were 1.0, 1.2 and 2.5 for the water, organic, and clastic frasti cns , respectiveiy. The weight of each component was obtained hy ~raviwtricineans, and the wei yhts converted to volumes using the assumed densities. The advantage of the method lies in the use of re latively accurate Rass determindtions, rather than the nore uncertai n vol umetri c measurements. Departures from the assumed component densi ties will affect the actual values obtained, but the error should be constant throughout the core, and should not affect subsequent interpretation.

-Sedimentation-- - - Rate AS though the varve counts plotted in Figure I. 1 provide an unusually good chronology for the core, the data have severe limitations as estimates of point sedimentativn rates. Average values of the sedi- mentation rate over the ten cent imetre counting intervals should be relatively accwate, but the pol 1en deposi tion rate calculation requires estimates for the two centimetre sampl i ng interval , values which may be quite different from the overall interval average. If the overall average is used, any deviations from that average value wi 11 appear in the fina: pollen diagrm as uncontrolled errors. Further, as there are marked differences in apparent sedimentation rate between count sections, xhe use of average values would result in abrupt changes in the apparent pollen deposition rate in the resulting pollen dsagram. The errors and interpretation difficulties so introduced may be to1erable in cores covering long time spans and dramatic changes in regional wgetation type, bvt woui d Fsse severe problems of i nterprctation under condi tions of a short time span and relatively subtle vegetation changes as were expected at Twin Lake. Such errors would be relatively minor under conditions ai a stable sedimentation rate, but there was evidence at

Twin Lake of mrked changes in the rate of sediment influx, particularly in the c'ldr; ti c coripcnent (Chapter VI) . Under these cclndi tions , it was j~dged Twin Lake - sedimentaiior; rate

L-, 0 100 200 300 LOO 500 60 0 700 800 Years before 1975

Fig. 1-1 - Twin Lake; sedimentation curve determined from varve counts. that the mezn sedimentation rates over the various core segnlents were inadequate for detailed calculations of the p~11cnaeposi tion rate.

An attempt was made to overcome this problem using estimates derived frilrn a pred-i ctive model of sediment2 ti on rate. Sedimentation retes are a iunctio~of severdl factors: the rate of influx of clastic and orpnic compo~er~ts,the amount of water trapped within the sediments, and compacti~r. Ccmpaction is related to the mass of the overlying material, and hence to depth within the core. It was possible to develop a nu1 iipl e regression model of the s~dimmtationprocess, using the mean 10 GTl, sedimentdtion 13ates as the dependent variable, and correspondi~gmcaq values for depth, water content, relative clastic and organic wlumes, loss on ignition, and sediment density as potential predictive variables. The final equatfen from this analysis expressed sedimentation rates as a function of the logarithm of depth, the percentage loss on ignition, and the percentage cf the sample vol u~ne composed of clastic materials, in the form

R = .?27866 (percent clastic volume) + .00189 (%loss on ignition) - .21616 (Logl0 Depth) - .18571. The analysis yield2d a coefficient of mu1 tip1 e correlation of ,9493, and an F ratio of 18.34, which with 3 and 6 degrees of freedom is well above tile .@Iprcbahili ty level (F.01 equais 9.74). Figure 1.2 shws a plot of residuals and a comparison of the estimates w'th the original values . The predictions are moderately close, with 95 percent confidence limits indicating an error term of about 35 to nO percent. ?here is some apparent tendency for the 0 0

1 .I -75 .Z -25 3 Actual Value /

Actual Value Ficj. 1.2 - Resideals and predicted values from sedirr~entationrate regressior:. Predicted values are shown with 95% confidence I imits . estimates to be conservative; to underesti~atehigh values and to over- estimate low ones. Pollen deposition rates based upon such estimates may he expected to show a reduced range of variation as a result. Sedimentation rates over the two centimetre sampling intervals were estimated fi-om the equation and the requjred sediment parameters.

This rvxessitated the use of values beyond the range of the original avcrzge vaiues used in ti12 analysis. The error term for these extreme values is unknown, but the analysis of the original residuals suggests that the values obtained are probably conservative. Estimated two centimetre sedimentation rates are shown in Figure I .3. These estimates were then used to calculate estimates of the pollen deposition rate shown in Figure 1.4.

-Results and Discussion The most striking feature of the sedimentatfon rate estimates is their great range and variability. The estimates span a range of between .03 cm. and .41 cm. per year, a difference of 1366 percent, and fluctuate widely withln a few centimetres of core length. Actual year to year variation may be still greater, for even the two centimetre samples represent time integrals of up to 25 years. Even if the vari- ahjlity is somewhat exaggerated by these estimates, it would seem that the vat-*;aiiot: in sedimentation rate at Twin Lake is far greater than that represected by the average 10 cm. varve values. Use of the average values in calculation of the pollen deposition rate would thus result in large errors, far greater than the 300 percent given by Davis et al. (1973) as typical of sing72 basins. The steep slopes and high erosion potential in the Twin Laice I-asin pr-esmably account for the highly variable ritte of sedimet:t inf?ux. -1 -1 actual

( estimate

-IT~-p--- Sedimentation Rate 12345 m. m./yea r

Fig. 1.3 - Tbii 9 Lake -- plot of observed sedin~entationrate and estimated 2 cm. rates.

The pol len diagram (Fig. 1.4) which restilts from these calcula- tions retains a high degree of variability, despite these attempts at correction. There is a high degree of positive correlation among ecologically distinct groups, such as krtemisia and the forest trees, and between most taxa and the i nfl ux of fi~e charcoal, i ndicati ng that much of the variation derives from residua1 variation in the sediment- ati~rirate, ar in the pollen deposition process, rather than from real changes in the vegetatf on. Some of this variation must result from residual errors in the sedimentation rate estimates, but two further causes may be suspected. The first is thzt basins such as this are known to change their pollen sampling characteristics over time, as the hasi n configuration is a1 tered by sediment accumulation (Lehman, 1975;

Davis, et a]. , 1975). Such changes may account for the increasing values of all taxa observed in the upper two thirds of the core. Secondly, there is a pcssibility of redistribution of sedinent within the basin, by turbidity flows or other mechanisms. Cushing (1973, p. 28) noted that pollen deposition rates at Lake of the Clouds, Minnesota, increased following fire and high charcoal influx, just as they do at Twin Lake, and postulated that increased wind action caused the near shore sedi- ments t~ be reworked, and deposited in deeper areas. This is not, however, a probable inechanisrn in this case, as the surrounding hills provide much of the wind protection at Twin Lake, and the surrounding forest reia.tively little. l'wo further variati~nsof this idea were considered. Crowder and Cuddy (1973) and Peck (1973) have documented the movement of pollen in surface drainage waters, and Peck has demonstrated that much of this po!len is derived from erosion of upland soils. High pollen deposition rates at times of fire and erosion nay thus be due to the influx of this renarked material. This hypothesis may be tested by reconsideration of

Figure 6.11, reproduced here as Figure I .5. If pollen influx increases at times of accelerated erosion, and hence at times of low loss oti ignition values, it would be expected that such events would produce strong posftive residuals in the low loss on ignition railge. Recall that the line shown is calculated on an assumption of constant pollen i nf1 ux. As no such residuals are present, i t may be concl uded that little reworked pollen is entering the core site in this way. If the reworked material comes fvom within the lake, and wave erosion is an improbable source, it may be hypothesized that the high deposition rate events result from turbidity flows caused by overloading of the submarginal slopes during extrem2 erosion events. Such flows must entrain or disp2ace pollen bearing sediments from the submarginal siopes, which then reach the deeper parts of the lake as large incre- ments in both sediment and pollen deposition. Stratigraphic evidence for such flows was noted in Chapter VI. A one centimetre flow would represent more than twice the maximum annual increment from the sedi- txentaticn rate estimates, and more tnan 30 times the rni;nirnum estimate. This is a real cknge in pollm deposition rate, but it is related to the sedimentation process within the lake, not to rcujonal vegetation chamjc, in spite of the fact that Figure 1.4 probably represents a reasonably kccurate picture of pollen deposition rates wi thi n Twi n Lake, interpretation of vegetation change from such data must be exceedingly cornpl ex. It was deci'ded, therefore, to restrict the vegetation i nter- pwtati on tc the percentagz and pol 1en concentration representations .

In spite of the failure to derive usable vegetation data, this analysis is of sonle value. The procedure for the dcterniination of sanpie volumes appears to be an improvement on the rnore direct, but error prone procedures now in use. The analysis of sedimentation rates should serve as a wiirninu. Avcr-age sediinerttatfon rates based on a few radiocarbon da tes may mask very large variations which hi 11 ul timately appear as errors in any r'esu? tant pollen d.iagra!n. Such errors wi 11 be small if sedimentation rates are relatively stable, but in this case the deposi ti on rate representation offers few advantages over simple pol 1en concentrzti ons . Sedimentari on rate vzri ation may be estimated using paramters derived from a physical analysis of the sediment, and such analysis is advisable whenever deposition rate cal col ations are undzrtaken. The sedimentation rate equation presented here may be recalibrated fer other sites, and if seneraliy valid, may provide a means of refining the sedimentation rate estimates now commonly used. APPENDIX I1

List of Botanical and Common Names

Musci

Tortula ruralis

Pinaceae

Abies lasiocarpa (Hook. ) Nutt. A1 pine Fir Larix lvallii" Parl. Larch Larix occidental is Nutt. Larch Picea engelmanni Parry ex Engelm. Engelman Spruce Pinus a1 bicaul is Engelm. Whi tebark Pine Pinus contorta Doug. ex Loud. Lodgepol e Pine Pinus ponderosa Doug. ex Loud. Ponderosa Pine Pseudotsuga menzi esi i var. g1auca (Mi rbel ) Franco Doug1 as Fir Tsuga mertenmong. ) Carr. Western Hem1 ock

Grami neae Aqropyron spica tum (Pursh . ) Scribn. and Smith Bunchgrass Aqropyron trachycaulum Malte. equals A. caninum L. Bromus inermi s Leys . Bromus tectorum L. Cheatgrass Calamagrostis rubescens- - Buckl. Festuca idahoensis Elmer Koeleria cristata Pers. Junegrass Poa secunda equals P. sandberqii Vasey. Sporobol us cryptandrus (Torr . ) Gray Stipa comata Trin. and Rupr.

Juncaceae

Juncus L.

Sal icaceae

Populus balsamifera L. Bal sam Poplar Popul us tremul oides Michx. As pen Salix spp. L. Willow

Betulaceae Betula alandulosa Michx. Betul a occidental is Hook. Water Bi rch Alnus tenuifolia Nutt. equals A. incana (L.) Moench. Alder Polygonaceae

Eriogonum heracl eoi des Nutt.

Chenopodiaceae

Salsola kali L. Russian Thistle

Cruci ferae Sisymbri um a1 tissimum L. Tumbl ing mustard

Rosaceae

Purshia tri dentata Pursh. Greasewood

Capri foli aceae

Sambucus spp. L. Elder

Compos itae

Ambrosia spp. L. Ragweed Artemisia cana Pursh. Artemi sia campes tri s L. . Artemisia dracunculus L. frigida Willd. Pasture Sage, Wormwood 1udovi ciana Nutt. norveai ca Fries . tridentata Nutt. Big Sagebrush Artemisia tridentata ssp. vaseyana Mountain Sagebrush Artemi s ia tri fida eauals A. tri~artita Rydb . Artemisia tri furcata StepT;. ex spreng. Artemi s ia tri partita Rydb. Threetipped Sagebrush dimo,~..'L- "I"" .Antennaria .. . - - . . Balsamorhiza- sag1 ttata (Pursh. ) Nutt. Centaurea diffusa Lam. Knapweed Chrvsothamnus nauseosus (Pal 1,) Britt. APPENDIX 111

QUADRAT DATA AND ACTUAL POLLEN COUNTS SITE A - 3m2 Quadrats

Date -1 2 3 4 5 6 7 - - - P - - 19/8-73 6 13 13 2 1 1 7

------0 SUM 44 29 32 15 3 1C 29 SITE C - 2rn2 Quadrats-

-Date 1 2 34 5 --7 9 11 12 13 14 1.5 16 Q.P.*.- 1974

-- --- SUM 15127543 2 135 2 7 BROKEN 2 TOTAL15127543 4 135 2 7

------

J( Q.P. = (&arter Point Sample W+N w+J

I-'

+ t-' +Or c1 I-' 288 2 -SITE E - 3m --Quadrats

-Date 1 2 3 4 5 6 7-- 8 9 10

SUI4 3.1 13 10 12 7 10 8 12 5 11 BROKEN 2 0 2 4 4 3 0 4 1 2 TOTAL 13 13 12 16 li 13 8 16 6 13 289 2 SITE F - 3m Quadrat

-----Date 1 2 3 4 -- 5 6 7 8 9 10 -.Q.P.*

193 3 1904 1902 A --- SUM 12 4 1 6 2 2 8 9 20 13 19 BROKEN I. 0 0 0 0 0 0 0 0 2 2 TOTAL 13 4 1 6 2 2 8 9 20 15 2 1 * Q.P. - Quarter Point Sanple 2 * SIlE G - 3m Quadrat

SUM 5 1 13 83 46 7 7 12 10 15 5 BROKEN 1 1 0 0 2 0 0 0 0 0 TOTAL 52 14 89 46 9 7 12 10 15 5 SITE ti - 3m7 Quadrats--

SUM 3 153522 12208424 2* SITE J - 3m Quadrats---

SUM 20 25 3 0 93 3 1 6 20 27 BROKEN 0 0 2 1 0 0 0 1 TOTAL 20 25 32 94 3 1 6 20 28 2 SITE K - 3m Quadrats-

--Date 1 2 .3 - 4 5 6 7 1974 1973 1972 I971 1 1970 3 1969 0 1 1968 3 1967 2 1966 7 1965 5 1964 1963 1 1962 1961 1960 1959 1958 1957 1955 1955 1954 1 1553 1952 1 1951 1950 1949 1948 1947 1 I946 1945 1944 1943 1942 1 1941 1940

SUM 24 2 1 16 0 3 12 3 RICHTER MARSH

1. Picea 2. Tsuga 3. Cupress aceae 4. Abies 5. Pseudotsuga 6. Pinus 7. Betula 8. Alnus 9. Salix 10. Populus 11. Grarni neae 12. Artemisia 13. Charcoal 14. Composi tae 15. Chenopodiaceae 16. Purshia 17. Cornus 18. Ambrosia 19. Dryopteris 20. Sel agi nel 1a 21. Trilete 22. Equi setum 23. Cyperaceae 24. Typha 25. Potamogeton 26. Indeterminate 27. Unknown

1 - 12 = pollen sum SICHTER MARSH - POLLEN COUNTS

Depth (cm) 1 2 3 4 5- 6 7 8 9 10 11 12 13 14 15- 16 17 18 19 20 21 22 23 24 25 26 27 TWIN LAKE

1. Picea 2. Tsuga 3. Cupressaceae 4. Abies 5. Pseudotsuga 6. Pinus 7. Betula 8. Alnus 9. Salix 10. Populus 11. Grami neae 12. Artemisia 13. Composi tae 14. Chenopodiaceae 15. Cornus Type 16. Ambrosia 17. Ranunculaceae 18. Sambucus 19. Purshia 20. Sel agi nella 21. Trilete 22. Equi setum 23. Dryopteris 24. Cyperaceae 25. Myri ophyl 1um 26. Potamogeton 27. Charcoal 28. Indeterminate 29. Unknown

1 - 12 = pollen sum 29 7

TWIN LAKE - POLLEN COUNTS Depth (cm) 1 2 3 --- 4 5 6 7 8 9 10 11 12 13 14 15 TWIN LAKE - POLLEN COUNTS (Cont'd)

Depth (c?) MAHONEY LAKE

Pi cea Potamogeton Tsuga Ruppi a Cupressaceae Charcoal Abi es Tubul i florae Pseudotsuga Chenopodi aceae Pi nus Ambrosia Betula Cornus A1 nus Cory1 us Salix Sambucus Popul us Ranunculus Grami neae 25. Purshia Artemi s i a 26. Selagine Cyperaceae 27. Trilete

TYP~~ 28. Dryopter

1 - 12 = pollen sum. MAHONEY LAKE - POLLEN COUNTS

Depth (cm) 12345 6 7 8 9 10 11 12 MAHONEY LAKE - POLLEN COUNTS (Cont'd)

Depth (cm) 13 1 15 16 17 18 19 20 21 23 22 24 25 25 27 28