Spatial and Chronological Patterns of Pushia

AN ABSTRACT OF THE THESIS OF

ROBERT JAMES SHERMAN for the M. S. in BOTANY (Name) (Degree) (Major) Date thesis is presented 7/O /3, /9c6 Title SPATIAL AND CHRONOLOGICAL PATTERNS OF

PURSHIA TRIDENTATA AS INFLUENCED BY

PINUS PONDEROSA OVERSTORY

Abstract approved Redacted for Privacy (Major professor)

Twelve sites of uniform topography and soils were selected in

the Pinus ponderosa /Purshia tridentata /Festuca idahoensis Associa-

tion. These sites were located in the rain shadow on the east flank on of the Oregon Cascades. A fire history in the form of fire scars ponderosa pine was available for nine of these sites. The bitter - brush populations on these sites were sampled at distances of 0 -34.5

feet from a large ponderosa pine which clearly dominated the area

for at least 50 feet. Density, cover, age, and clumping data for the bitterbrush were obtained. Density was found to be greatest on plots with the most recent occurrence of fire (22 years past). Cover was extremely variable within any one plot. Only slight variation was found in percent of live crown among the various plots regardless of their density or fire history. Age determinations using growth ring analysis or direct ring counts provided information indicating that although most bitterbrush do not survive a fire, sites are rapidly repopulated and generally show a peak repopulation year within 20 years after burning. Plants on sites with most recent fire tended to show more rapid height growth than did plants on "old" sites. Most "old" sites presently have a rather uniform age class profile with only slight indications of peak germination years. Most age class profiles do not fit a concave survivorship curve. Rodent caching as evidenced by plants growing in clumps was found to occur extensively on all sites. Most of the one year old clumps were large with as many as 21 living plants encountered. Progressive reduction in clump size probably occurs both through rodent browsing of young plants and later through moisture stress.

By the time a clump has attained an average age of 30 it is likely that only two or three individuals remain alive.

The question of the perpetuation of bitterbrush in the absence of fire may be raised. Present fire control practices which allow extensive litter accumulation, especially on mesic sites, are resulting in an elimination of suitable planting sites for bitterbrush and may favor other species from more mesic associations less dependent upon fire and litter removal for their continued existence. SPATIAL AND CHRONOLOGICAL PATTERNS OF PURSHIA TRIDENTATA AS INFLUENCED BY PINUS PONDEROSA OVERSTORY

ROBERT JAMES SHERMAN

A THESIS submitted to

OREGON STATE UNIVERSITY

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

June 1966 APPROVED:

Redacted for Privacy Professor of Botany In Charge of Major

Redacted for Privacy

Head of Department of Botany

Redacted for Privacy

Dean of Graduate School

Date thesis is presented 7-77 /3 )/fa Typed by Opal Grossnicklaus ACKNOWLEDGEMENTS

I wish to thank the many people who assisted me during the course of this study. Doctors H. K. Phinney and F. H. Smith were particularly helpful in the formulation of a suitable growth ring analysis technique and with technical problems related to presentation of data.

I am especially grateful to my major professor, Dr. W. W. Chilcote, both for introducing me to the study area and for the many hours he has devoted to advising me in this work.

I also wish to express my sincere thanks to Mr. Francis Voytas and Mr. Gerald Benson of the Sisters Ranger Station. The information gained from discussions with these men contributed immensely to my understanding of the study area.

To my wife, Barbara, for assistance in the field, typing and reading of the manuscript, and patient understanding, I am eternally grateful. TABLE OF CONTENTS

INTRODUCTION 1

DESCRIPTION OF STUDY AREA . . 3

Physical Features 3 History 6

METHODS 10 Plot Selection 10 Sampling Method 13

RESULTS 20

Overstory . . 20 Fire and Other Disturbance 21 Bitterbrush Density Patterns 22 Bitterbrush Cover Patterns 23 Bitterbrush Age Class Distribution 30 Clumping of Bitterbrush 43

DISCUSSION 68

CONCLUSIONS AND SUMMARY 76

BIBLIOGRAPHY 78

APPENDIX 81 LIST OF FIGURES Figure 1. Topographic map of the study area showing location 4 of plots (U. S. Geological Survey Map, Sisters Quadrangle, Oregon. 1959).

2. Cross section of fire scarred ponderosa pine. 8

3. Detailed view of multiple fire scars on a ponderosa 8 pine near Plot C.

4. Photographic view of Plot G illustrating the clearing 8 effect around a mature ponderosa pine.

5. Photographic view of Plot I, illustrating concentration 8 of bitterbrush at the base of a mature ponderosa pine.

6. Photographic view of Plot D. 12

7. Photographic view of Plot F. 12

8. Photographic view of Plot H including a completely 14 sampled transect.

9. Cross section of a bitterbrush root crown as used 14 for growth ring analysis.

10. Typical prostrate growth form exhibited by bitterbrush 14 plants in areas of heavy litter accumulation.

11. Adventitious root formation from a bitterbrush stem 14 buried in deep litter.

12. Schematic plan of a sample plot with transects, 15 quadrats, and cover sample areas shown.

13. Average density of bitterbrush plants per plot in 24 relation to the number of years since last fire (grazing disturbance on Plot K).

14. Bitterbrush density patterns as related to distance 25 from plot center. LIST OF FIGURES (CONTINUED) Figure

15. Bitterbrush density patterns as related to distance 26 from plot center.

16. Representation of the relative amounts of bitterbrush 28 cover by quadrats on the four transects extending outward from the center tree of each plot.

17. The relationship between time since fire and the 32 percentage of plants on a plot with decayed centers.

18. Age class profile of Purshia tridentata for Plot D. 34

19. Age class profile of Purshia tridentata for Plot G. 35

20. Age class profile of Purshia tridentata for Plot F. 35

21. Age class profile of Purshia tridentata for Plot E. 36

22. Age class profile of Purshia tridentata for Plot M. 37

23. Age class profile of Purshia tridentata for Plot C. 37

24. Age class profile of Purshia tridentata for Plot H. 38

25. Age class profile of Purshia tridentata for Plot B 39

26. Age class profile of Purshia tridentata for Plot L. 40

27. Age class profile of Purshia tridentata for Plot I. 41

28. Age class profile of Purshia tridentata for Plot J. 41

29. Age class profile of Purshia tridentata for Plot K. 42

30. Relationship between average age of bitterbrush 44 and distance from center tree.

31. Relationship between average age of bitterbrush 45 and distance from center tree. LIST OF FIGURES (CONTINUED) Figure

32. Average height of bitterbrush plants according to age. 46

33. Average height of bitterbrush plants according to age. 47

34. One year old clump of 13 bitterbrush. 48

35. Twenty, one year old bitterbrush seedlings 48 representing a single clump.

36. Ten year old clump of eight bitterbrush. 48

37. Clump of four bitterbrush with plants of two different 48 ages.

38. Percentage of clumping observed according to location 50 of plots within square mile sections extending from west (mesic) to east (xeric).

39. Percentage of bitterbrush clumping observed on study 51 plots in relation to the number of years since last fire.

40. Average number of bitterbrush per clump as related 53 to average age of clump.

41. Pictorial scatter diagram showing the interrelationships 55 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot D.

42. Pictorial scatter diagram showing the interrelationships 56 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot C.

43. Pictorial scatter diagram showing the interrelationships 57 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot F.

44. Pictorial scatter diagram showing the interrelationships 58 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot E. LIST OF FIGURES (CONTINUED) Figure

45. Pictorial scatter diagram showing the interrelationships 59 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot M.

46. Pictorial scatter diagram showing the interrelationships 60 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot C.

47. Pictorial scatter diagram showing the interrelationships 61 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot H. 48. Pictorial scatter diagram showing the interrelationships 62 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot B.

49. Pictorial scatter diagram showing the interrelationships 63 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot L.

50. Pictorial scatter diagram showing the interrelationships 64 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot I.

51. Pictorial scatter diagram showing the interrelationships 65 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot J.

52. Pictorial scatter diagram showing the interrelationships 66 between age, distance from the tree, litter, and clumping for bitterbrush plants sampled on Plot K. LIST OF TABLES

Table

1. Climatological data for Sisters, Oregon. 5

Appendix Table

Sample plot overstory data 81 SPATIAL AND CHRONOLOGICAL PATTERNS OF PURSHIA TRIDENTATA AS INFLUENCED BY PINUS PONDEROSA OVERSTORY

INTRODUCTION

This study involves a structural analysis of one of Oregon's simpler climax forest communities described by Dyrness (1960) and

Volland (1963) as the Pinus ponderosa /Purshia tridentata /Festuca idahoensis (As sociation This association is extensively represented in a narrow north -south belt along the east flank of the Oregon Cas- cade Range, a region characterized by coarse textured volcanic soils, and declining precipitation associated with the "rainshadow effect" exhibited on the leeward side of this mountain range. Particular attention is directed to the antelope bitterbrush (Purshia tridentata (Pursh)DC)1 which occurs as the only shrubby understory species in many areas. This shrubby understory forest layer is unique in that in nearly all cases it is perpetuated from seed in which rodent planting is thought to play a significant role. It also has ring porus xylem and normally produces obvious growth increments. Thus, age of individual plants can be determined with relative accuracy.

Because of these unique features of this association and its location within a sharp climatic gradient, a study designed to

1 Scientific and common botanical names follow Peck (1961). 2 determine the variations in overstory influence on the spacial and chronological patterns of bitterbrush distribution was developed.

It is hoped that through a better understanding of this simple synusial relationship an insight into the more complicated forest associations involving a larger number of tree and shrub species may be obtained. 3

DESCRIPTION OF STUDY AREA

Physical Features

A small segment of the ponderosa pine belt ranging from 121°34' to 121°41' west longitude and from 44°19' to 44°25' north latitude was selected for study (Fig. 1). Plots were located within these boundaries in a loose transect arrangement running northwest to southeast. The elevations in this transect vary only a few hundred feet from Suttle Lake (elevation 3438 feet) to Sisters, Oregon (eleva-

tion 3186 feet). Soils along the transect are relatively young and

uniform mixtures of pumice and gravelly glacial outwash (West, 1964).

Probably the most striking aspect of the east flank of the Cas-

cade Range is the specially rapid transition from the maritime clim-

ate of the west to the nearly continental climate of the east. This continental climate is most clearly demonstrated by temperature and

precipitation records from the U. S. Forest Service Ranger Station

at Sisters (Table 1). In general, Sisters receives small amounts of precipitation distributed more evenly throughout the year than the

precipitation of maritime locations (Wells, 1941). Sisters also has greater seasonal temperature extremes which tend to accentuate the

low level of annual precipitation. Unfortunately, weather records from Sisters are incomplete. In addition, data that is available 4

Figure 1. Topographic map of the study area showing location of plots (U. S. Geological Survey Map, Sisters Quadrangle, Oregon. 1959). Table 1. Climatological data for Sisters, Oregon.

13 Year Record -- 1921 -1934 (West, 1964) Average precipitation in inches Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Ann.

2. 64 1.94 1.16 . 85 1.09 . 68 .68 . 32 . 86 1.05 3.24 2. 14 16.65

Recent Records ( Climatological data, 1958 -1965) deviation Average precipitation in inches from Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Ann. Median

1958 ------.28 .36 2.99 1.07 ------1959 2.57 1.84 .75 .12 .46 .34 .05 .11 .53 .81 .45 .59 8.62 -7.28 1960 1.55 2.22 3.31 1.02 .54 .02 .05 . 17 . 19 .66 4.55 1.80 16.08 + . 18 1961 .84 3.78 1.43 .66 .84 .68 .04 .06 .55 1.44 4.64 3.20 18.16 +2.26 1962 1.87 1.50 1.63 .65 1.09 .04 .01 .48 .35 2.30 2.03 1.90 13.85 -2.05 1963 2.21 1.92 1.07 1.01 .78 .39 .36 .20 .67 .26 2.66 1.41 12.94 -2.96 1964 3.48 .02 .71 .26 .07 .62 .09 .16 .02 .23 2.30 12.24 20.20 +4.30 1965 3.05 .38 .10 .98 .20 .84 1.37 1.59 .07 .35 2.15 .72 11.80 -4.10

Average temperature (F. ) Extremes Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Ann. High Low

1958 54.4 47.8 38.9 38.0 45.4 100 7/22 -11 1/4 1959 33.7 - 32.8 38.7 43.7 45.8 56.7 63.8 58.8 53.0 47.5 38.4 31.4 1960 26.0 31.3 38.8 43.3 46.9 57.3 66.0 59.1 56.0 47.5 35.4 31.1 44.9 99 7/18 -12 2/27 1961 34.5 39.4 38.3 43.4 48.2 60.9 63.3 66.1 50.6 45.5 34.3 31.5 46.3 98 7/12 - 8 12/11 1962 29.7 33.4 36.7 46.4 46.2 55.1 60.7 59.4 55.6 46.1 40.1 35.3 45.4 95 7/23 -28 1/22 1963 27.3 41.4 36.8 40.3 50.2 54.5 58.0 61.6 60.9 47.7 39.0 32.4 45.8 99 9/27 -16 1/12 1964 33.2 36.3 36.8 40.5 46.8 54.4 61.4 58.5 51.5 46.6 34.0 29.9 44.2 99 7/27 -16 12/17 1965 32.9 37.6 36.5 43.6 46.1 55.1 62.7 61.3 50.3 50.4 39.6 30.3 45.5 92 7/16 - 2 12/17 6 must be applied to the study area with caution due to the location of Sisters at the extreme east end of the transect. Also, summer precipitation results from storm cells which move rather erratically from south to north as well as in the more typical west to east pattern.

History

Another outstanding feature of the ponderosa pine forest, prior to its present form of management by lumber interests, was its re- peated burning. These fires were nearly always very mild, rarely resulting in a crown fire. They typically produced a partial burning of litter, light brush, and dead snags as a fire passed through an area and produced a forest, the appearance of which has been described by Weaver (1961) as park -like. These fires often originated natur- ally as the result of lightning or Indian game drives, but as early lumbering developed, many logged areas were cleared of slash by

"broadcast burning" (Benson, 1965). Ordinarily, the bark of mature ponderosa pine trees was adequate to protect the underlying cambial tissue from the rapidly passing fire. However, an accumulation of needle litter and wood near the base of a tree would fuel a fire to an intensity sufficient to consume the bark and kill the cambium on one side of a tree. Once this fire scar or "cat face" was formed, susceptibility to subsequent fires increased markedly (Soeriaatmadja, 7

1965). The pattern of cambial regrowth on scarred trees serves as an excellent record of fire occurrence in an area (Figs. 2 and 3).

Since the establishment of fire control practices in this area, the incidence of widespread fire has been greatly reduced. The effect of this change in fire history is of great significance to any biological study of the area.

The management of this region with respect to its major re- source, lumber, has varied according to the land ownership patterns of the last century. Ln the 1870's the control of much of this land was transferred, on an alternate section basis, from government hands to T. E. Hogg, under terms of a railway construction agreement. However, the railroad was never constructed through this area and the land passed to the control of J. J. Hill (Brogan, 1964).

In the 1950's many of the same sections of land were reacquired through purchase or trade by the government in an attempt to "block up" government ownership and thereby improve Forest Service management efficiency. But, prior to repurchase, much of this land under Hill ownership had been logged and in general is now classified as RP4 (residual overmature ponderosa pine) (Voytas, 1965). This is particularly true of land near the community of Sisters, Oregon.

In the mid 1930's many sections were cleared of nearly all timber that was then considered merchantable (Benson, 1965). This is borne out by the classification of this land on the Forest Type Map 8

f '

3. view Figure 2. Cross section of a fire scarred Figure Detailed of multiple fire ponderosa pine. scars on a ponderosa pine near Plot C.

irj t .V.; Fa 1! .y. t t1,4111. t. ( , I IN 7 " 7%0 ; ef

, V .--, ,I.,..), V " V _14 qi1 i s.:.iÌ)il..' t ,' q A. Sri. i... ,,,, :, .11.-44.,,.--- e-._ 7,..,..,...:. i it4'. 1- ', 4 44,w ,. - ...., 7, 1.. li ...... * _ .. 1 .r.-14.1 b %-4t. - 4 - 4,:-;,..-.L. -!1',,IN.,.;_ grIffi *4.-44.1.-'44" - -.4p,""- 'r A. ' ..- :151.!1!, ....7: : .. :fi- .:...: , 'ronsor. -;:'< l'`-' '''Ir- A . s, '' ",,,,,....:,;-...... 4 , TVet.." -, -..r: ' a f - - . - . 'r:;.. C`==i.i

Figure 4. Photographic view of Plot G Figure 5. Photographic view of Plot I. illustrating the clearing effect illustrating concentration of around a mature ponderosa pine. bitterbrush at the base of a mature ponderosa pine. 9 of Oregon prepared by the Forest Survey Staff in 1936 (U. S. Forest

Service, 1936). In addition to logging, disturbance to the area also occurred in the form of extensive seasonal sheep drives from 1880 to 1908 (Brogan, 1964). These spring and fall drives usually passed through or slightly north of Sisters, along the Santiam wagon road to a point known as the Graham Corral (Fig. 1) and then on to various summer pastures in the high Cascades. Benson (1965) reports that these seasonal drives slowly diminished in magnitude until about 1940 when they were completely abandoned.

Following World War II, the management of this region has tended toward light selective cutting, pruning and thicket thinning.

The disturbance from these practices has usually been light and especially spotty. Evidence of this light disturbance usually re- mains clear for many years due to the low level of precipitation.

Therefore, one may select practically any area for investigation and effectively recognize much of this kind of unnatural disturbance. 10

METHODS

Plot Selection

A major consideration in selection of sample areas was the

relationship of tree and shrub synusia. In order to simplify this relationship as much as possible, it was decided to locate large ponderosa pine trees which were slightly set apart as individuals from the general stand. Thus, changes in pattern as one sampled at various distances from this tree could be related to the changing influence of the single tree rather than the combined influence of many trees. Uniformity in pattern and composition of the understory were also considered to be of great importance. Again, an attempt was made to keep plots as simple as possible. Therefore, areas that did not obviously represent the Pinus ponderosa /Purshia tridentata /Festuca idahoensis Association were eliminated as possible study sites.

In summary, plots were selected to meet six major criteria. These considerations included:

1. Freedom from major disturbance, including cutting and heavy deer browsing.

2. Suitable overstory conditions, i. e. , an area in which a single ponderosa pine clearly dominated the site for at 11

least 50 feet in all directions.

3. Uniformity of vegetation in which relatively pure stands of ponderosa pine, bitterbrush and fescue were typical.

4. Availability of a natural record of fire very near to the site.

5. Nearly level topography

6. Location of the plot to assure suitable distribution of plots along the east -west transect and thus along the moisture gradient.

Following extensive reconnaissance from June 15 to July 10,

1965, 12 areas, designated B through M, in order of selection were found which satisfied most of these requirements (Fig. 1). However, the last three plots, K, L, and M, did not have a fire history available. A tentative plot designated "A" was used to evaluate bitter - brush sampling techniques. Because this plot did not satisfy the above requirements, it was omitted from further consideration.

Examples of areas selected are shown in Figures 4, 5, 6, 7, and 8.

As may be determined from Figure 1, most plots were located along U. S. Highway 20. This location is in large part due to the fact that this land is under government ownership and is not as intensively logged as nearby Brooks -Scanlon land. Also, the Forest

Service has tended to leave a scenic protection strip along both sides of the highway. 12

, - átr. -- . .

Y hi%li v .! . `_'.lì

. 'i w +t " f ,. l, t'; ' T +_... !i; wyo : '. Y.,, 1.-I, ^r.,` y ` A ,r..{ .i ; iN, ':j.^ ,o 1. ,.,. fY / , w N9 , i r d . r Y' Figure 6. Photographic view of Plot D.

^,, , IwN'

d r. i e.:- .4,1ktow

H% I. Vt ry 0:.r _ ; ` T' °` , r . , , , CO . - tiT f t. r . , ¡ "* 4rf*, >.`" t`'.: w,. Alit. .`4Y:ditár-, .i, Figure! 7. Photographic view of Plot F. 13 Once plots were located, they were identified by attaching a standard Forest Service square metal tag to the large ponderosa pine which was designated as the plot center. This tag included plot des-

ignation by letter and orientation (compass bearing) of the four sam-

ple transects radiating away from the tree, as well as the date of

first sampling on the plot and the name of the author.

Sampling Method

The 12 plots shown in Fig. 1 were sampled in alphabetical

order. Initial sampling of Plot B began July 14, 1965. Final bitter -

brush samples from Plot M were examined on August 30, 1965.

The primary intent of this study was to establish the distribu-

tional characteristics of bitterbrush with respect to the pine over -

story. A circular plot of slightly less than .1 acre in size was

laid down around the ponderosa pine selected to be a plot center

(Fig. 12). To assure a degree of objectivity in collection of bitter - brush samples, each plot was divided into four quarters by drawing

a north -south and east -west line through the center of the plot. With-

in each of these four segments, a rectangular transect 33 feet long

and three feet wide was laid out with its origin 1. 5 feet from the center tree, thus extending 34.5 feet from the tree (Fig. 8). This was visually oriented within the quarter of the plot in such a manner that it would include as much of the bitterbrush cover as possible. 14

ke t' 4.1"e. i. - ' . 'i y- .. `R l."r ' 'At 1:11 'M{`^ e'r_ f r ; r -- . 17-.5 '!t- ph / rjCc _ + * ; 4 ti 1 ;' ° i ' .zoo_ ` . '...ti;:- K -- . ` ,¡ L'i`t ' °er : v .±,111-' , ,:.4.^., °,.3i'.iti7.,:,:..-. 1 _i ?r ' 7 .°P:+fi Ar - ." Ct.;t `h_i. : .:r r r:. .Ilrd.:i`'''.éi+i Ti R. .. .i

Figure 8. Photographic view of Plot li Figure 9. Cross section of a bittcrhrisb including a completely sampled root crown as used for growth transect. ring analysis.

H - Ac=:

L . L

. 41" g.

Figure 10. Typical prostrate growth form Figure 11. Adventitious root formation exhibited by bitterbrush plants from a bitterbrush stem buried in areas of heavy litter accumu- in deep litter. lation. 15

M E

Figure 12. Schematic plan of a sample plot with transects, quadrats, and cover sample areas shown. 16

When possible, transects were centered in each quarter of the plot.

The outer limit of each transect centerline was then permanently marked with a wooden stake.

Transects were subdivided into 11 three foot square quadrats designated by numbers one through 11 starting from the center of the plot. In some cases, bitterbrush was found in the first space between the origin of the transect and the center tree. These spaces were designated by the number O. As quadrats were examined the percent cover by species was estimated from a one foot square quadrat nested in the lower right corner of each large quadrat.

The cover estimates included total horizontal area occupied in the space zero to two inches above ground surface. This usually resulted in total foliage cover estimates for prostrate plants such as strawberry and basal area estimates for bitterbrush and young ponderosa pine. The percentages of the square foot occupied by litter and bare ground were also estimated. This latter (bare soil) estimate was considered to be of possible significance in rodent caching. Any pine seedlings occurring outside this cover sampling area but still within the quadrat were recorded, clumping was noted, and the individual heights were estimated. Each bitterbrush plant was then cut from the quadrat, assigned a transect, quadrat, and individual number. The occurrence of plants in clumps, evidence of resprouting, and adventitious root formation were carefully noted. The 17

maximum height of each plant was measured to the nearest one tenth foot. The maximum crown diameter and the crown diameter at a right angle to the first diameter determination were measured

(the right angle measurement was omitted on plots B, C, D, and part of E) also to the nearest one tenth foot and recorded.

It has been found by Talbert (1960) in studies of bitterbrush of known age that the root crown portion of the shoot root axis provided the most accurate material for age determination. Therefore, approximately three inches of the axis including the root crown was removed from the plant with an axe. Originally, when sampling Plot

A, this section was allowed to dry for several days and then an attempt was made to smooth the section. This proved to be less effi-

cient than working with freshly cut material. Therefore, a micro -

tome straight razor which was stroped frequently was applied to the

freshly cut surface to produce a smooth cut (Fig. 9). This was then

examined at the plot using a B & L dissecting microscope at 10 or

20x. Diffuse lighting conditions usually prevailed. The angle at which the cut surface was held was usually varied several times to

insure the clearest possible view. If the detail of the growth rings was still not clear, a phloroglucin stain was brushed on the material and was observed as it developed the characteristic red color (Stew- art, 1930). This was usually sufficient to make ring counts possible.

The number of rings counted and the occurrence of any unusually 18 narrow rings was recorded. If estimates were necessary due to

center rot this was recorded as a separate figure added to the number of rings actually counted. Due to the variation in clarity of

rings, a notation of confidence was made with each actual count.

This was based on a three point scale recorded in field notes as C,

U, and D indicating certain determination, uncertain determination, and definite error respectively.

In order that stands might be compared for relative density of ponderosa pine overstory three measures were taken. The basal area per acre was calculated directly from tree diameters and also determined by the Bitterlich prism method (Dilworth, 1965).

A third comparison of overstory conditions involving shade class patterns was made on a number of stands on October 31, 1965.

This was done by placing an insolation grid (Wagar, 1964) in the center of each of the 44 quadrats on each plot sampled. This device superimposes the canopy and a 100 dot pattern which is designed to include all arcs of the sun from March 21 to September 21. The dots are arranged to compensate for variation in insolation intensity.

Therefore, shade during the morning and evening hours is measured as relatively insignificant compared to an equivalent amount of shade falling on an area during the hours in the middle of a day.

In order that the age and rate of growth of the center tree might be estimated, an increment core was taken. A core was also 19 takenfrom an approximately six inch DBH tree near the plot. This second core was taken with the hope that relative ring width would reflect recent growing conditions in the area (Roughton, 1962). These cores were glued in the grooves of a corregated cardboard, sanded, and relative ring widths were measured to .1 mm with a homemade comparitor. 20

RESULTS

Overstory

Basal area determinations based on either the Bitterlich method or as calculated from actual measurements of DBH show a tendency for mesic plots to have more extensive tree cover (Appen- dix). This is probably due to variations in natural growth patterns along the moisture gradient and the extensive cutting experienced on the more xeric plots.

Shade patterns were determined for only five of the 12 plots.

These figures, considered on a quadrat by quadrat basis, show re- markable uniformity within individual plots, especially since the sampling points progressively vary in location from three feet to 33 feet away from the tree trunk. Because of this apparent uniformity in shade values no attempt was made to investigate possible correla- tions between these patterns and bitterbrush distribution. The average shade value and the range of values for each plot are shown in the Appendix. The estimated ages and DBH of all plot center trees are also recorded in the Appendix. These trees were selected because they were somewhat separated from the rest of the overstory and because of their obvious dominance of what was to become a study plot. The diameter and age data indicate that these trees have 21

been a significant overstory factor for some time.

Attempts to establish a denrochronological scale based on relative ring width from ponderosa pine increment borings were

unsuccessful. Measurements of ring widths from 23 specimens were

made and plotted graphically in an effort to correlate years of low

or high growth increments (Roughton, 1962). Different patterns of

growth could not be reconciled by consideration of multiple or absent

growth rings. The difficulty in this attempted correlation is appar-

ently due to the use of overmature trees which have added only very

small growth increments in the last 50 -100 years. Also, many of the specimens were from mesic sites considered as relatively in-

sensitive by Keen (1937).

Fire and Other Disturbance

Fire histories, as determined from fire scarred ponderosa pine are presented with the bitterbrush age class profiles (Figs. 18 through 29). These data are primarily intended to indicate the most recently recorded occurrence of fire on each plot. However, on many plots earlier scars were of sufficient clarity to estimate the time of occurrence of those fires. For example, the pine section from plot C is shown to have burned at least six times in approximately 110 years (Fig. 3).

The absence of fire in the last 30 years is very clear. Benson 22

(1965), the Fire Control Officer at Sisters, could remember no fires in the study area since his initial association with the area 30 years ago, except for possible slash burning adjacent to U. S. High- way 20. This may explain the 22 year old fire scar found on Plot E. This plot is located about 100 yards from Highway 20.

Several plots, G, M, L, and K did not have nearby trees which exhibited fire scars. Perhaps these plots have escaped serious fires.

The bitterbrush age class distributions in time and litter conditions of

Plots M and L tend to support this idea. However, the age classes of Plots K and G are very young. This is easily explained for Plot

K by the occurrence of a form of disturbance other than fire. Sheep drives often passed over this plot prior to 1940 (Benson, 1965).

The fire history of Plot G is uncertain. This plot is located within 500 yards of Plot F which has a 35 year old scar. The great

similarity in the bitterbrush age class structures on the two plots may be considered to indicate similar fire history. However, the litter depth on Plot G is more typical of a plot that has not burned for some time.

Bitterbrush Density Patterns

A total of 2, 052 live bitterbrush plants were cut from the 12

plots. A total of 13 plants from plots D, F, H, L, and M were found

to exhibit adventitious root formation from prostrate branches (Figs. 23

10 and 11). These plants commonly appeared as two separate plants but upon removal of the usually deep litter there could be no doubt as to the true origin of the "second" plant. In all instances these plants were counted as only one plant. The density in terms of number of plants per plot2 is illustrated in Figure 13. Plots with more recent disturbance consistently show greater density values.

The average number of bitterbrush found at a particular distance from the center tree is determined by combining density data from all four like numbered quadrats on each plot. These data are presented in Figures 14 and 15. The actual values for quadrat 0 have been multiplied by 9/5 due to the smaller size of this quadrat.

The mesic plots definitely have the highest number of plants in quadrats located farthest from the plot center. Thus, the most mesic plot, D, and the most xeric plot, K, have entirely reversed density patterns.

Bitterbrush Cover Patterns

The two measures of total horizontal crown diameter were averaged and the resulting number was considered as the diameter of a circular crown. The area of this crown was then calculated using the formula D2 x . 7854 = area. These cover area data were

2The area sampled on each plot equaled 416 square feet. Figure

number of bitterbrush per 416 sq. 13. 400 300 200 COO Average (grazing relation density .E disturbance to 25 the R .1 f of number Number bitterbrush 50 .0 .0 on of Plot .5 years of K). years 75 .M plants .I since per last 100 plot fire M in 21+ Figure k.0 4- M .fl S 4.0 V- .O tn 0" .L1 y.! .I.J A) L L n N O. G) L O Q a.i C 7 E a) L >- 4) C - number of bitterbrush per 36 sq. ft. ' 14. 30 40 50 20 40 50 2 30 10 40 50 30 10 20 I0 0 Bitterbrush Quadrat from I 2 3 plot 4 PLOT PLOT PLOT number 5 center. 6 0 0 P density 7! (extending 9 10 II patterns outward o as I 2 related 14 from PLOT PLOT PLOT i center 6 to E N C 7 distance 6 9 tree) 10 Il 25 Figure VO 4- 4- ..o .c M 4-0 .- .o -] 0 4-J -I L L 3 D. a) L tn Cr in 4- E a) L O o a) C >. -1 15. Density number of bitterbrush per 36 sq. ft. 30 40 SO 40 20 JO 50 10 40 20 20 30 50 10 10 Quadrat from Bitterbrush plot PLOT PLOT number PLOT center. 6 density e M L 8 (extending 9 10 patterns It outward as . I related 2 from 3 4 PLOT PLOT PLOT center 5 to 6 J I K distance 7 8 tree) 9 IO 11 26 27 then totaled on the basis of quadrats, transects, and plots. A complete recalculation of cover based on percent live crown was also made. The results were surprisingly uniform for both quadrats and plots. On all plots except Plot F this live crown adjustment resulted in a cover evaluation equal to 52 -67% of total crown cover. Recently burned plots showed only a slight tendency to have a greater percentage of live crown. Plot F, an unusually vigorous stand, had a live crown area equal to 90% of the total crown cover.

Total crown cover is used in the following discussion and in Figure

16.

As previously mentioned, only one measure of crown diameter was made on Plots B, C, D, and a portion of E. In order to obtain a more realistic determination of plot cover, the quadrat cover totals from Plots B and C were adjusted by using data from Plot I.

The cover values for Plots D and a portion of E were adjusted by using data from the remainder of Plot E. In both cases the determination of the adjustment factor involved calculation of the cover using only one measure of crown diameter and comparing this with the cover calculated for the same plants when two measures of crown diameter were employed. The resulting adjustment factor for Plots D and E was . 666. The adjustment factor for Plots B and

C was .738. Application of these adjustment factors to individual plants was recognized to be unrealistic. However, multiplication Figure

Transect number 2 16. 4 3 2 4 3 2 3 3 4 2 4 1 2 ' 2 4 3 4 3 I 0 r + . a - 1 cover Representation from e r r 2 u + al + old . r M r . + -- 3 AS .r Quadrat - - - r + -`! 111 4 r - . .A - . . - the . P . PLOT PLOT PLOT P P by r + L ,- .. 6 r + L L . . . . O O O e .. r - T - . 6 r r r - T - - . center quadrats T . . 0 6 r F N E C ... r -- - 7 / r number - - . . r r - _ - B ./ - - - . . . . , -r ..1 . . 9 . - ... - - - of . - r -, + r r tree .. + 10 r - - .r. . . . on i r the r .11 . 1 -4 - - - . of the relative each four g Ir. J 0 1 1 ' 1 1 r al li .0 r ./ r 1 r d i r - - plot. r at .d transects ~ 2 r r r r r ++ Si r +r amounts all r r will _ 3 ./ r _ Quadrat . . ..1 d r 011 4 r _ r . - P . PLOT PLOT PLOT . PLOT P .. . ./ L 111 S we r r L O ilr .1. O . - T - we 6 s T . - . of . . H r B ..1111 ... i extending I r L K J r aA 7 mg - . . number . , + r bitterbrush .A r B + o+ r 0/ d ---- - te am r r - 9 Id - / - . r .A + r f0 r r .. r r r r 11 _ El in ale a. . outward 28 29

of quadrat totals by the adjustment factor was deemed necessary to properly represent quadrat and plot cover.

These cover data (including the adjustments for Plots B, C,

D, and E) are graphically illustrated in Figure 16. In this figure each plot is represented by four horizontal rows of shaded blocks which represent relative amounts of cover. Each row represents a transect and is arranged with quadrat "O" to the left and quadrat

11 to the right. Because quadrat "O" is only 5/9 the size of all other quadrats the cover values from these quadrats must be regarded as absolute values rather than expressions of true cover - sample area ratios.

The lack of homogeneity of bitterbrush cover is obvious from this figure. There are many cases in which a quadrat with relatively heavy cover is bordered by one or sometimes two quadrats with vir- tually no bitterbrush cover at all.

What is considered to be one of the most striking features of the bitterbrush distribution is visually apparent in Figure 16. The more mesic plots have a rather complete exclusion of bitterbrush from the low numbered quadrats (near the plot center), while the most xeric plots (I, J, and K) have high cover values for the quadrats nearest the plot center. The xeric plots also have more higher numbered quadrats that completely lack bitterbrush. These contrasts are illustrated by Figures 4 and 5. 30

There are conflicting reports in the literature with respect

to resprouting of bitterbrush from the root crown following fire.

Nord (1959) reported very slight resprouting in study areas in Cali-

fornia. Blaisdell (1956) reports extensive resprouting on stands of

bitterbrush found in Idaho. Only five specimens of the 2, 052 exam-

ined in this study gave evidence of resprouting. It is therefore con-

sidered reasonable to consider all bitterbrush plants as having originated directly from seed.

Bitterbrush Age Class Distribution

The growth rings in root crown portions of all bitterbrush plants were examined in the manner described on page 17. As data accumu-

lated, a dendrochronological pattern which involved the presence of

narrow rings for the years 1955, 1947, and 1944 became evident in

many of the specimens from more xeric sites. This pattern became

a very valuable tool in determining ages of specimens with suppressed

outer rings. In fact, it was even possible to determine the year of

death in specimens that had died since 1955 and thus contained the

narrow 1955 ring. The occurrence of this narrow ring is in agree-

ment with the work of Stanton (1959) who reported noticeably narrow

growth rings for the year 1955 in his bitterbrush- sagebrush associa-

tion which would be slightly more xeric than the plots I have desig-

nated as xeric. No official weather data are available from Sisters 31 for that year, but Benson (1965) remembered 1955 as a very hazard-

ous fire year due to low precipitation in the Sisters area. On the

mesic sites no such pattern of narrow rings could be discerned and age determinations were restricted to direct growth ring counts.

Stanton also found it necessary to estimate missing center

growth increments. He reported estimation to be necessary on only

two to five percent of his samples (Stanton, 1959). My data indicate

11. 8% of the plants collected to be devoid of one or more center

rings. Usually this involved estimates amounting to about five years but on some older plants estimates as high as 15 years were con-

sidered to be justifiable. The percent of the total plot sample found to be missing center rings is indicated in Figure 17. Plots which do not show fire disturbance for long periods tend to have the greatest portion of the total stand with dead centers.

The results of these investigations of age structure appear in

Figures 18 through 29. Plots are identified by letter and arranged in a series in order of increasingly more xeric location. In the preparation of these age class distribution histograms the portion

of each age class which involved either estimation due to rotted

center or material classified "D" in actual ring count is indicated by the dashed portion of the vertical line.

Nearly all bitterbrush examined were less than 50 years old.

However, on Plot L a number of plants were estimated to be in the Figure Ii 72, Fi

17. Percent of plants in stand with decayed centers 20 30 10 40 percentage The relationship .E 25 of Time plants .6 .F elapsed between 50 .0 oá.à .0 time since .s plot since 75 .M with last .I decayed fire fire 100 and (years) .J centers. L .M the 32 33

50 -60 year old category and one plant, the oldest found on any plot, was estimated to be 85 years old.

The close correlation of bitterbrush age classes with fire history is very clear. Plots with a history of recent fire (D, E, F, G) have much younger stands of bitterbrush. Most of these plots have very few plants that extend back in age beyond the most recently indicated fire. Apparently only isolated plants survive when fire sweeps through an area. These survivors are probably a very important seed source for repopulation of burned over areas. Nearly every plot, regardless of the present age of the stand was found to have a peak in the age class profile occurring about five to 25 years following the most recent fire. This burst of repopulation is apparently followed by a gradual reduction in the magnitude of addition of younger age classes to the plot. It is very difficult to determine from these data specific years that were favorable or unfavorable for bitterbrush establishment. The possibility exists that a given set of conditions favorable for one plot are unfavorable for another. Fur- thermore, as previously indicated, precipitation during the growing season is far from uniform in distribution.

The average age of bitterbrush found at a particular distance from the center tree is determined by combining all four like-numbered quadrats on each plot. This results in a maximum of 12 average age determinations per plot. These figures are presented - - E3timated occurrence of fire 20 ------Indicates the portion of age class based on estimation 18 -

5 16- .. u 4 14 - U wti 12- a 10- 8- a m ti o., 6- 4-

2- :

- 11111 I1 II1:::I It l l 75 40 45 SO 55 60 65 70 Age 5 10 15 20 25 30 35 r46 '21 '16 '11 '06 1901 1896 1891 Year '61 '56 '51 '41 '36 '31 '26

number of specimens examined= 197. Figure 18. Age Class Profile of Purshia tridentata for Plot D. Total

w fP Percent of ' in Each Age Class Figure Sample 18 20 10x- 12 14 16 2 4- 6 8 Year Age ------r - 19. Age Total '61 5 Class number '56 10 Profile of specimens - -- of '51 - 15 - - Purshia -- class Indicates Estimated '46 20 examined tridentata based '41 the 25 occurrence on = for portion 293. estimation Plot '36 30 G. of of age fire '31 3S a :' . Percent of Sample in Each Age Class 22 24 18 e 10 12 14 16 6 Figure Year Age , 20. '61 S Total Age Class '56 10 number Profile I '51 of 15 - -`Estimated specimens ----- of I Purshia '46 20 I Indicates class examined tridentata based '41 25 the occurrence on = portion for estimation '36 30 173. Plot of of 1 1 F. '31 35 age fire Percent of Sample in Each Age Class 26- 2 22- 24- 1 1 1 1 1 0 4 6 8 Figure 8 0 2 2 4- 6 ------Years Age 11 21. '61 S Age Class '56 10 Profile '51 15 of Purshia '46 20 I tridentata 25 '41 for '36 30 Plot E. '31 35 Total '26 40 number - '21 of 45 "'-- - specimens '16 class Indicates Estimated 50 based examined 55 '11 the occurrence on portion estimation = 60 '06 378. of of 1901 age fire 65 1896 70 1891 75 a ó H w .4 d U á ó á d u á cn .8 w u ... a`"i v ca v 1.:1 ti u ovo u Percent of SamplePs in Eachts Age Class5 10 10 12- 2- 4 6 8- 2 4- 6- 8- Year Age - ,- Year Age II I I Figure Figure '61 '61 5 S (111111 23. 22. I '56 10 '56 10 Age Age 1 Class Class '51 15 '51 15 l,I1 Profile Profile iii '46 '46 20 20 of of I Purshia Purshia 1 '41 25 '41 25 I , tridentata tridentata I 1 l '36 30 '36 30 I1 , for for '31 35 35 '31 Plot Plot C. M. I '26 40 '26 40 I Total Total I I 1 I, ll , number '21 '21 45 number 45 , - of ' '21 of '16 50 50 "' specimens " - specimens II "" class Indicates Estimated '11 '11 55 55 based examined= examined '06 60 the '06 60 occurrence on portion estimation = 1901 1901 129. 65 65 178. of of age fire 1896 1896 70 70 1891 1891 75 75 Percent of Sample in Each Age Class 20- 22- 14- 16- 18- 10- 12- 2- 4- 6- 8- Year Age Figure '61 5 I 24. i 1 Age 1 '56 10 Class 1 1 '51 15 Profile 1 1 i of '46 20 Purshia 1 1 1 '41 25 tridentata ii1 '36 30 1_,II,i111, for Plot '31 35 H. Total '26 40 i ' number ' -- '21 45 1I ; of I specimens '21 50 Estimated ' I class Indicates i based '11 55 the examined occurrence on portion estimation '06 60 = of of ,,;i 192. 1901 age fire 65 1896 70 1891 75 Estimated occurrence of fire

Indicates the portion of age class based on estimation g 12 Also fire scar for 1865 - ú 10 m

6 fi

Age 5 10 15 20 25 30 35 40 45 50 55 60 6S 70 75 Year '61 '56 '51 '46 '41 '36 '31 '26 '21 '16 '11 '06 1901 1896 1891

Figure 25. Age Class Profile of Purshia tridentata for Plot B. Total number of specimens examined = 66. Estimated occurrence of fire

------Indicates the portion of age class based on estimation 14-

NM fa Ú 12- 4) b0

,G 10 U tti W Gf. 8- a) v) 6- o v 4- ti v I

; 2 III I II III III :HI i 1 I Age 5 10 1S 20 25 30 35 40 45 50 S5 60 65 70 75 80 85 Year '61 '56 '51 '46 '41 '36 '31 '26 '21 '16 '11 '06 1901 1896 1891 1886 1881

Figure 26. Age Class Profile of Purshia tridentata for Plot L. Total number of specimens examined= 90. .0 1 5 Percent of Sample in Each Age Class Percent of Sample in Each Age Class 10- 12 2 4 4 6 8- 2 6- 8- Year - - - Age ` - Year Age I '61 '61 5 5 Figure Figure I '56 '56 10 28. 10 27. I Age Age 1 1 '51 '51 15 15 1 Class Class 1 1 '46 Profile Profile 20 '46 20 of of '41 I I I i 1 25 '41 Purshia Purshia 25 II , 1 ; i I I I I , i '36 '36 tridentata tridentata 30 30 I I 1 I '31 '31 35 35 for for 1 Plot Plot '26 '26 40 40 J. I. H 1 Total Total I ! '21 45 '21 45 1 number 1 number IIii!ii ' Ì '16 '16 50 50 - of of ¡ I I i I specimens specimens 1 I I i class Indicates Estimated '11 '11 55 55 I I 1 based '06 examined examined 60 '06 the 60 occurrence on portion estimation Fire 1901 1901 65 65 = = of 97. scar 86. of age I fire 1896 for 1896 70 70 1860 I 1891 1891 -4" 75 75 Percent of Sample in Each Age Class 18 20 22 10 12 14 16 2 4 6 8 ------Year Age Figure '61 5 I 29. '56 Age 10 Class I 111 '51 15 Profile I '46 20 of I Purshia I I '41 25 I tridentata Il 30 '36 I: for III '31 35 Plot K. '26 40 Total ;;I number Sheep '21 45 drive - of '16 SO specimens - disturbance I class Indicates Estimated '11 55 based examined the '06 occurrence 60 on portion estimation _ 173. 1901 65 of of age fire 1896 70 1891 75 43 graphically for each plot in Figures 30 and 31. In nearly all plots the average age is shown to decline as distance from the plot center increases.

The height to age ratios for each plot are presented in Figures

32 and 33. Only plants designated "C" and "U" in the field notes (see above) are represented. A height /age calculation for each one year age class from one to 30 is included. Because of the reduced numbers of plants older than 30 years and the probability of greater actual error in age determination, height to age ratios for the higher ages are represented in ten year categories, i. e. 31 -40, 41 -50,

51 -60, 61 -70, 71 -80. In this way location of points based on data from only one or two plants is largely eliminated. The pattern of these growth curves appears related to the histories of each particular plot, with the most rapid growth occurring on the most recently burned sites. However, the fact that the more recently burned plots are generally located at the most mesic end of the transect must also be considered.

Clumping of Bitterbrush

The occurrence of closely associated bitterbrush in clumps was found to be very common (Figs. 34 -37). Presumably, these clumps are the result of germination of unrecovered rodent caches.

The rodents involved in this caching activity are believed to be Figure

in 30. Average age years 20 3 40 50 30 40 50 30 40 SO 20 10 20 I0 10 0 distance Relationship Quadrat 1 2 3 4 number PLOT PLOT PLOT 8 from i 0 i i between 7 center 8 (extending 9 10 I1 average tree. outward age 0 1 2 of from 3 bitterbrush 4 PLOT PLOT PLOT S center 6 E M C 7 8 tree) 9 and 10 I1 44 Figure á m in years 31. Average age 30 40 50 40 50 20 40 50 20 30 IO 2 30 t0 Quadrat distance Relationship I 2 3 4 PLOT PLOT number PLOT 5 from . 6 H . L between center . 8 (extending 10 II average tree. outward age 1 of 2 from 3 bitterbrush 4 P PLOT PLOT LOT center 6 I J 7 K 8 tree) 9 and 10 II 45 Average height in feet 20 40 30 4.0 5.0 t0 3C SC 2C 10 Figure 25 25 PLOT PLOT 32. G D 50 50 Average height 75 75 of bitterbrush 25 25 Age PLOT PLOT in F E plants 50 50 years according 75 75 to age. 25 PLOT PLOT M C 50 75 1.1. Average height in feet 20 40 5.0 2. 3.0 1.0 .0 Figure 25 PLOT PLOT 33. M II Average SO height 75 of bitterbrush 25 Age PLOT PLOT in plants L I years SO according 75 to age. 25 PLOT PLOT S R SO 48

.Sei t_ 4111r,1

Figure 34. One year old clump of 13 Figure 35. Twenty, one year old bitterbru: bitterbrush. seedlings representing a single clump.

J i

S^ +, y ¡!i ', r, 0.

IA.i. ì-. +.'.r R .Y n` . X+: , n tr.! 7 iÿ ;;r;(11;. :T .. S - ..,F.. i _: 3 ;` `

Figure 36. Ten year old clump of eight Figure 37. Clump of four bitterbrush with bitterbrush. plants of two different ages. 49 primarily the golden manteled ground squirrel, Citellus lateralis and the yellow pine chipmunk, Eutamias amoenus (Gordon, 1943).

Data relating to the abundance of these clumps is presented in two different ways in Figures 38 and 39. The upper lines in these figures are drawn to agree with points indicated by circles. The location of these points on the ordinate is determined by dividing the total number of bitterbrush in clumps by the total number of bitterbrush in the plot sample area and multiplying by 100, i. e. n /N X 100% = % c clumping. The lower lines are drawn to agree with the x's. These points are located on the ordinate by dividing the total number of clumps on a plot by the number of clumps plus the number of bitter - brush occurring as single, unclumped plants and multiplyingby 100, i. e.

C /(C +U) X 100% = % clumping. These methods demonstrate very close agreement in assessment of the extent of clumping, but the latter method consistently yields a lower value for clumping.

By either method the percent of clumping figures, when compared with plot location or time elapsed since last major disturbance on the plot, indicates greatest clumping on mesic plots.

The initial size of bitterbrush clumps is apparently governed by the size of rodent caches. Stanton (1959) reported finding clumps which included as many as 74 seedlings. The largest clump encountered in the sampled areas in this study consisted of 21 one year old plants. The smallest clumps were of course composed of two plants. Figure

38. Percentage of clumping extending plots Percentage Location (mesic) GO eo different 30 40 so 70 in 20 10 the x° 0 within x6 P.F x, figure to of from calculations east of 2 x .E plots E .M xN square clumping by west (xeric). 3 "X" within mile to and 4 observed east used sections square "V (See xc S N ".) xN to 5 .e x e .1- Xt. assess text mile according I x i extending .3 xJ i for .x sections x K clumping explanation to from location as west shown of of 50 Figure

Percentage of clumping 39. 20 30 40 50 60 70 eo DO 10 culation$ plots figure fire. Percentage Number in XE by .E (See 25 relation "X" used xi il of xr X. .6 of text and bitterbrush to years for 50 " assess to xo .0 xc .c ".) explanation the since XI .. clumping number clumping last 75 xM= of xj of fire of as years observed different shown 100 xJ .a since xl- XM .1. .M in on cal- the study last 51 52

Certainly there must be individual plants which though now unclumped are the sole survivors of rodent caches. Therefore, all percent clumping determinations are undoubtedly underestimates.

Stanton (1959) reports observation of clumps in which all individuals were not of the same age. Apparently all viable seeds in a cache may not germinate in the same year. The plants from such a clump are shown in Figure 37. This clump of four plants contained two, two year and two, one year old plants. The variation in age of plants within a clump necessitates averaging ages of all plants within the clump when comparisons of clump size or clump location with clump age are made. This approach was used in the preparation of

Figure 40 and Figures 41 through 52. Figure 40 may be considered to illustrate the decline in number of survivors as a clump becomes progressively older. Initial clump reductions were often observed to be the result of rodent browsing. Later death is probably due to moisture stress. This decline is very rapid in the first ten years of clump existence and then slowly levels off to a point where clumps with an average age greater than 25 years have an average size of less than three plants. However, once this reduced clump size is attained it is apparent that several bitterbrush can live together to a very old age.

The location of clumps of bitterbrush with respect to the ponderosa pine in the center of the plots is of great interest. This Figure Average number of individuals per clump 2.0 5.0 GO 40. clump Average average 1O size number age is of calculated clump. of 20 bitterbrush Average (Beyond by 30 age ten per 30 of year clump years clump 40 age age as in classes.) related years average SO to 60 70 54

"pattern" is illustrated by means of scatter diagrams (Figs. 41 through 52). These figures are based on the methods utilized by

Anderson (1940) to express, simultaneously, variation in more than two dimensions. These diagrams include four variables: location of the clump with respect to the plot center, average age of the clump, the number of individual plants in the clump, and a combined expression of litter and ground cover values for the quadrat in which the clump occurred. The following scale and symbols were devised to combine litter and cover into four classes:

Class Symbol 95 -100% litter = 1 = 100% total cover

75 -94% litter 75 -100% total cover = 2 =

50 -74% litter <50% litter or - 3 = 50 -100% total cover 100% total cover

< 50% litter = 4 = <100% total cover O In general, litter is inversely proportional to the distance from the center tree. On most older plots, litter has accumulated around this tree to a depth of nearly one foot and often results in the partial burial of bitterbrush plants near the tree. Litter usually diminishes to a depth of one or two inches at a distance of eight to ten feet from the tree and bare patches of soil may be exposed beyond that. This diminution is due to deposit of both bark and needle Figure

of 41. Average age clump Quadrat of for between Pictorial Short litter seedlings bitterbrush lines 1 is age, number scatter indicated if- x at distance in CJy y r periphery (extending x V plants a diagram clump. by from (- degree sampled s of outward showing the r circles e of on tree, T J, shading J. Plot the from indicate e litter, interrelationships center D. b di 9 (see Amount 1E and the o tree) text). clumping number of 55 Figure

42. Average age of clump Quadrat of Short between Pictorial 50 for 20 30 40 litter 60 10 seedlings 0 bitterbrush lines is age, number scatter indicated 2 at distance in 3 periphery (extending a plants clump. diagram 4 by from degree sampled s of showing outward the i circles of on tree, leit #ÒE- shading 60 Plot the from o # indicate litter, e interrelationships center G. g6d4:4 ( (see Amount 4E yy and the tree) text). %tkv dyJ# clumping a number of 56 Figure

of 43. Average age clump of Pictorial Quadrat Short for between 20 30 litter 40 50 10 60 0 seedlings bitterbrush 1 lines is age, number scatter indicated 2 at distance in 3 periphery (extending a plants clump. diagram 4 by from 5 degree sampled of outward showing 6 the circles of on tree, 7 shading Plot from the d e indicate litter, interrelationships F. center 9 (see -Od Amount 10 and the text). tree) el- 11 clumping number of 57 Figure

of 44. Average age clump Quadrat of Short for between Pictorial litter seedlings bitterbrush lines is age, number scatter indicated at distance in periphery (extending plants a clump. diagram by from sampled degree of showing outward the circles of on tree, shading Plot the from indicate litter, interrelationships E. center (see Amount the and tree) text). number clumping of 58 Figure

Average age of clump 45. of Pictorial Quadrat Short for between 30 40 50 litter 20 60 10 0 seedlings bitterbrush 4- t lines is age, number if* scatter indicated 2 at distance in 4A 3 periphery (extending a plants clump. diagram by from 6- 4 5 degree sampled of outward showing 41E ir- r the 6 circles of on tree, 7 4- shading Plot the from r e 6- d indicate litter, interrelationships M. center 1F g ! (see 6- Amount 10 ei 6 the and text). tree) tt 6 4 clumping number of 59 Figure

46. Average age of clump of Quadrat Short for between Pictorial litter 30 40 s0 20 w 60 seedlings 0 bitterbrush 4- lines I is age, number scatter indicated y 2 at distance in 3 periphery (extending a plants clump. diagram 4 by from degree sampled S of showing outward the 6 circles of on tree, 7 shading Plot the from S indicate litter, interrelationships C. center 9 (see Amount # IO the and text). tree) I clumping I number of 60 Figure

of 47. Average age clump of between Quadrat Short for Pictorial litter seedlings bitterbrush lines is age, number scatter indicated at distance in periphery (extending a plants clump. diagram by from degree sampled of outward showing the circles of on tree, shading Plot from the indicate litter, interrelationships H. center (see Amount and the text). tree) number clumping of 61 Figure

48. Average age of clump Quadrat of Short for between Pictorial litter 40 50 30 60 20 10 seedlings bitterbrush 0 lines is I age, number scatter indicated 2 at distance in periphery (extending a plants 3 clump. diagram by 4 es- from degree sampled 5 of showing outward the circles 6 of on tree, 7 shading Plot the from indicate 8 tr- litter, interrelationships center B. (see 9 Amount and the 10 tree) text). clumping number 11 of 62 Figure

Average age of clump 49. Quadrat of Short for between Pictorial litter 20 30 10 40 50 60 seedlings o bitterbrush lines 4- is number age, scatter indicated 2 4 4- 4 * at distance in 3 periphery 4 (extending 4- 4- a plants clump. diagram 4 4 4 by from degree sampled 5 of outward showing the 6 4 circles 4- of on tree, 7 6- d shading Plot from the 6 indicate 4 litter, interrelationships center L. 9 if (see Amount 1O and the tree) text). 11 number clumping of 63 Figure

of 50. Average age clump of Short between Pictorial Quadrat for litter 20 30 40 SO 60 lo i seedlings O bitterbrush IV lines I is age, number scatter indicated 2 at distance in d 3 periphery (extending a plants clump. diagram 4 str by from degree sampled 5 of outward showing the 6 d circles of on tree, 7 +C shading Plot from the e 5 indicate litter, interrelationships center I. 9 if (see Amount IO d- the and text). tree) I I clumping number of 64 Figure Ó op Average age of clump 51. Quadrat of Short for between Pictorial litter 20 30 40 50 10 60 seedlings e 0 if bitterbrush lines 1 is age, number scatter indicated e 2 if at distance in if Y 3 4' periphery (extending plants a clump. diagram 4 a by from sampled degree 6 of outward showing the i V circles of on tree, 7 ö shading Plot the from 6 indicate litter, interrelationships J. center 9 e (see Amount IO +C X a the and text). tree) I I number clumping of 65 Figure

52. Average age clump of between Quadrat Short for Pictorial litter te 30 40 50 60 a a a 0 seedlings bitterbrush 4 lines I is age, number scatter indicated 2 at distance in 4 a 3 ii( periphery (extending a plants clump. diagram 10 4 a a a a by from 6 degree sampled of showing outward the df- 6 circles of o on tree, 7 shading Plot the from indicate litter, interrelationships K. center 9 (see Amount 10 and the text). tree) I I clumping number of 66 67

litter at the base of a tree while only needles are deposited farther away from the trunk.

Distribution of clumps with respect to average clump age and

distance from the center tree appears to be related to litter condi-

tions. Young clumps with large numbers of individuals have a tendency to be located in quadrats toward the outer edges of the plot.

Old clumps, usually of small size do not exhibit such great exclusion from plot centers. Therefore, old clumps may occupy both interior and outlying quadrats. Since young bitterbrush clumps are generally excluded from the plot centers, the resulting scattergram patterns often are triangular in shape. 68

DISCUSSION

The methods utilized in this study are judged in general to have been successful in achieving the desired goals. The plot location criteria eliminated many undesirable variables without making location of study areas completely impossible.

Fire histories, when obtained, proved to be quite clear and "datable. These histories are judged to agree very closely with other site factors such as litter and bitterbrush age classes. Unfortunately, all mesic plots have evidence of relatively recent fire while the xeric plots do not. This makes separation of the effect of moisture conditions and fire history next to impossible. This problem is further compounded by a general tendency for mesic plots to have a greater overstory cover than xeric plots.

The lack of weather data from 1934 to 1958 is most unfortunate since many of the bitterbrush sampled are estimated to have begun growth in that time period. Weather patterns based on ponderosa pine growth increments have been determined in this region by Keen

(1937). However, these studies require a much more extensive sampling than taken by this author and become an end in themselves.

The actual sampling techniques employed are thought to pro- vide a representative sample from each plot. Longer transects out from the plot centers may have provided a clearer picture of 69 variation of bitterbrush distribution in space. This is undoubtedly true for Plot K where there was very little bitterbrush beyond 35 feet from the center tree.

The variability in bitterbrush patterns with respect to center trees is seen in general to correlate with ground litter distribution.

Three major factors govern the quantity of litter on a plot. These factors are: rate of litter production, rate of decomposition of litter, and the time elapsed since litter was last removed from the site by fire. The absolute values of these three variables are not known but it is clear that xeric sites, even though they have not burned recently, tend to have lower litter accumulation. This may be attributed to either low production or accelerated decomposition but it is more likely that both factors contribute to this condition.

The influence of litter on understory plant distribution may be due to factors other than the physical presence of the litter. Zinke

(1962) has shown significant change in pH, nitrogen level, and min- eral exchange capacity with respect to distance from isolated mature ponderosa pines. Zinke attributed these variations in soil chemistry to variations in litter deposit patterns. However, this author feels that, for the purpose of this study, the physical presence of litter is more important than secondary chemical influence.

It is unlikely that significant planting by rodents occurs in heavy litter. During the course of this study many rodents were 70 observed in their caching activities. In practically every instance these activities were confined to areas in which litter was very light or essentially absent. Therefore, as time since the last fire becomes progressively greater and litter around trees becomes more extensive, rodent planting is limited to areas farther from the individual trees. Clump distribution patterns which show the direct evidence of rodent planting patterns seem to support this premise.

It is only rarely that clumps of young bitterbrush are found growing in heavy litter. However, old clumps are found both in heavy and light litter. This occurrence in heavy litter should not be unexpect- ed because these clumps were probably planted prior to litter accumulation.

If present fire control practices are maintained, it appears that on mesic sites these older clumps will eventually die of old age. Since regeneration here is difficult, areas devoid of bitter - brush will tend to develop around larger ponderosa pine trees. This trend may be noted for plots D and G (Figs. 41 and 42).

The age determinations of bitterbrush specimens are thought to be reasonably accurate. Roughton (1961) observed only 2. 1 percent error in dating plants of known age in Colorado. This study has no absolute evaluation available for the method since no bitter - brush of certain age were available for test purposes, but an indication of accuracy may be present in the age class profiles. In several 71 instances the populations of recently disturbed plots (Plots D and E) are found to have obvious peak years. In both cases, these peaks are accompanied by a substantial representation in the one year younger age class. Perhaps the secondary "peak" is an artifact due to errors in growth ring analysis. Even if this is true, the average errors in age determination would generally be well under 10 %.

Thus, a plant estimated to be 20 years old could easily be 19 or 21 years old. But this is certainly not enough to affect any of the conclusions involving age, especially since care was taken to segregate plants of doubtful age from calculations where specific age was of greatest importance. This problem of error in aging was most noticeable in age determinations of clumped plants. It is probable that all of the seeds that give rise to a clump are planted at the same time. Most likely those that are capable of germination do so the following spring. Therefore, one would expect most young clumps to be composed of plants of the same age. Only a few examples

(Fig. 37) were found where this was definitely not the case. How- ever, not enough clumps in the one to five year age category were encountered to definitely resolve this problem.

The tendency toward a sigmoid configuration (Odum, 1959) is noted in many plant height -age growth curves. What might be termed a "lag" phase apparently exists until the onset of a "log" phase sometime between years five and 15. The duration of this 72 linear growth phase is quite variable from plot to plot and in most

cases its upper limit is difficult to determine. However, as one

views the actual stands of bitterbrush it is apparent that under the ponderosa pine canopy this upper height limit is usually from three

to four feet. Most plots are shown to approach this maximum in the

older age classes, but, the mere inspection of plant heights on a

site may give one very little indication of bitterbrush age. Plots

with recent fire reach a height of three to four feet in 25 -30 years

while plots with no evidence of fire for 100 years may have only 60 to 75 year old plants near four feet high.

Several plots, for example D and I show evidence of senescence

in the older age classes. In a number of cases, old plants (age

greater than 50 years) were observed to be broken down and had

come to assume a somewhat prostrate growth form. This usually

was noted in areas toward the centers of mesic plots where litter

was extensive. It is thought that heavy snow cover coupled with

this litter accumulation probably results in deformation of these plants.

One plot (B) is shown to have a rather great maximum height

growth for an "old" plot. This may be due to the removal of the two large ponderosa pines from this plot in 1962. It has been ob-

served in many situations (Benson, 1965) that removal of the pine overstory or overtopping of other shrubby species (Stanton, 1959) 73 allows established bitterbrush to grow well above the usual maximum.

The plot density values in Fig. 13 are apparently closely related to fire disturbance history. The location of Plots K, L, and M on the abcissa in this figure is uncertain. Plots L and M both lack available fire histories. As judged from litter conditions and bitter - brush age classes present, it appears that Plot L has not experienced fire for a long time. This is probably not true for Plot M. It appears by interpolation from density data that Plot M probably burned about

50 to 60 years ago.

Plot K is very difficult to categorize because of the unusual nature of disturbance. Interpolation from density data would indicate 50 to 60 years have elapsed since fire. This is in agreement with the lack of other factors which might indicate recent fire.

Both of these postulations with respect to Plots M and K are also supported by data from Fig. 17. Approximately 50 to 60 years since fire disturbance appears to be a likely estimate for these plots.

The age class patterns on many plots are difficult to interpret.

A preponderence of younger plants was expected for all plots with the age class profiles resembling a theoretical concave survivorship curve (Odum, 1959). Plot H is the only plot that approaches this hypothetical curve. Age class profile -fire history relationships may hold the key to an understanding of survivorship patterns. The 74 relationship of bitterbrush to fire in this area at any time other than the recent past may only be speculated. It may be possible that fires were once so frequent that bitterbrush could not establish it- self in this region. However, it is very difficult to imagine the present widespread distribution of bitterbrush occurring since the advent of fire control in the last 100 years. Apparently, plots are rapidly repopulated after fire. This rapid repopulation must be made possible by a surviving seed source nearby. Sweeney and Biswell (1961) report from experiments in broadcast burning of somewhat park -like ponderosa pine forests that many microsites remain unburned and that understory species would not be eradicated by fire of this nature. Rodents are the most likely carriers of bitterbrush seeds from survivors to burned over areas. Gordon (1943) reports transportation of seeds is usually limited to 300 feet. Therefore, it seems reasonable to assume that at least one bitterbrush per 90, 000 square feet must survive fire if rapid repopulation is to occur. After this rapid surge of repopulation it appears, from age profiles, that new seedling establishment is reduced but continues nearly every year. If this is the case, it is probable that older bitterbrush populations experience a gradual turnover until the recurrence of fire partially clears a site and makes possible another repopulation wave. Under these conditions it is likely bitterbrush would occupy this environmental niche for 75 many years to come. However, present fire control practices may greatly modify this projection. As Soeriaatmadja (1965) points out, when fires now occur after prolonged fire exclusion, the destruc- tion of nearly all plants in large areas is quite likely.

In general, all of these characteristics, the rapid repopulation of sites after fire, the pattern of rodent planting of seed in litter - free areas, and the pattern of senescence on some "older" (unburned) plots, point to bitterbrush as a fire adapted species, as is true of nearly all of the plants in this association. The present suppression of fire and the subsequent litter buildup, especially on mesic sites, will probably lead to conditions less suitable for bitterbrush habita- tion. Perhaps the shrub synusia will be entirely lost from this association and fescue will become the primary form of ground cover. On the other hand, litter may exclude practically all herba- ceous vegetation from more mesic plots and Abies grandis may eventually become firmly established. 76

CONCLUSIONS AND SUMMARY

Twelve sites of uniform topography and soils were selected in the Pinus ponderosa /Purshia tridentata /Festuca idahoensis Asso-

ciation. These sites were located in the rain shadow on the east

flank of the Oregon Cascades. A fire history in the form of fire

scars on ponderosa pine was available for nine of these sites. The

bitterbrush populations on these sites were sampled at distances of

0 -34.5 feet from a large ponderosa pine which clearly dominated

the area for at least 50 feet. Density, cover, age, and clumping data for the bitterbrush were obtained.

Density was found to be greatest on plots with the most recent

occurrence of fire (22 years past). Cover was extremely variable within any one plot. Only slight variation was found in percent of

live crown among the various plots regardless of their density or fire history. Age determinations using growth ring analysis or direct ring counts provided information indicating that although most bitterbrush do not survive a fire, sites are rapidly repopulat-

ed and generally show a peak repopulation year within 20 years after burning. Plants on sites with most recent fire tended to show more

rapid height growth than did plants on "old" sites. Most "old" sites presently have a rather uniform age class profile with only slight indications of peak germination years. Most age class profiles do 77 not fit a concave survivorship curve.

Rodent caching as evidenced by plants growing in clumps was found to occur extensively on all sites. Most of the one year old

clumps were large with as many as 21 living plants encountered. Progressive reduction in clump size probably occurs both through rodent browsing of young plants and later through moisture stress.

By the time a clump has attained an average age of 30 it is likely that only two or three individuals remain alive.

Clump distribution and litter distribution appear to be closely correlated. Most recently planted clumps were found to be outside of major litter deposit areas around ponderosa pine. Apparently rodents prefer to cache seeds in areas of essentially bare soil. The question of the perpetuation of bitterbrush in the absence of fire may be raised. Present fire control practices which allow extensive litter accumulation, especially on mesic sites, are resulting in an elimination of suitable planting sites for bitterbrush and may favor other species from more mesic associations less dependent upon fire and litter removal for their continued existence. 78

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Zinke, Paul J. 1962. The pattern of influence of individual forest trees on soil properties. Ecology 43:130 -133. APPENDIX SAMPLE PLOT OVERSTORY DATA Plot Basal area (sq. feet /acre) Shade values Age of DBH of Bitterlich Direct DBH average range center tree center tree method calculation (years) (inches)

D 80 67. 4 58.5 47-78 590 49. 5

G 60 52. 3 - 250 36. 8

F 60 45.2 42.7 36 -53 310 36. 4

E 100 109.4 -- - 150 26. 7

M 80 55. 0 - 540 45. 4

C 120 92.4 61. 5 50-75 280 38. 4

H 80 63.5 - 210 33. 4

B 60 68.9 -- - 250 (est.) 40. 0

L 30 33.7 - 260 43. 7

I 50 21.1 50. 9 45 -58 170 25. 5

J 50 51. 0 42.4 35 -55 380 31. 4

K 30 14. 0 -- - 110 28. 0