DISTRIBUTION AND IMPACT OF CRYPTORHYNCHUS LAPATHI (L.) (COLEOPTERA: CURCULIONIDAE) ON SALlX SPP. IN BRITISH COLUMBIA
Cynthia L. Broberg
B. Sc. (Plant Biology), University of British Columbia, 1997
THESIS SUBMllTED IN PARTIAL FULFILLMENT FOR THE DEGREE OF
MASTER OF PEST MANAGEMENT
in the Department
of
Biological Sciences
O Cynthia L. Broberg 1999
SIMON FRASER UNIVERSITY
October 1999
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The poplar and willow borer, Cryptorhynchus lapathi (L.), known to be present in British
Columbia since 1923, primarily attacks species of Salk and Populus. Larvae bore into stems, causing them to break easily. Its impact has been increasing in recent years due to the increasing importance of poplar and willow from both economic and ecological perspectives. I conducted a survey to document the distribution and prevalence of C. lapathi in B.C. within different biogeoclimatic subzones and Salix hosts, and to describe the between-tree and within- tree dynamics of C. lapathi. The sunrey spanned five biogeoclimatic zones, 15 subzones, 45 locations, 135 sites, and 3360 trees, 675 of which were measured in detail. The range of C. lapathi has at least doubled since 1963. The weevil was present in 38 locations and 14 subzones. The intensity of attack and the number of individual weevils were positively related to the prevalence of attacked trees (f= 0.701 and 0.562, respectively). The prevalence of weevil- attacked trees was significantly lower in cold than in warm subzones. Using available climatic data, three different regression models were derived using: number of months with mean ternperature >1 O°C (mode1 1); number of months with mean ternperature >lO°C, mean annual ternperature (OC), and number of frost tee days (model 2); and elevation (m), mean temperature warmest month (OC), and accumulated day degrees >5'C (model 3) to predict the proportion of attacked trees, al1 with ? XI.8. There were 11 new host records, but no evidence of host preference. In general, attacked trees were larger, had more dead wwd and stems, more adventitious branches per stem, more total breaks per stem, and more naturally-caused breaks per stem than their attack-free neighbours. Breaks caused by C. lapathi tended to be slightly larger in diameter and lower on the stem than naturally-caused breaks. Bases of stems were preferentially attacked, and C. lapathi selected large stems in which to oviposit. As large attack- free trees becorne less abundant, weevils apparendy start to attack small-diameter stems.
Although C. lapethi is advenely affecting the health of willows in B.C., there is no evidenm that any Salix species is threatened by weevil-caused extinction.
iii Well grandpa, here's to given'er snoose. Acknowledgements
I thank Kim Hardacker and Alton Harestad for helping develop the methodology used in the study; John Borden for his support and supervision; Margaret Gajecki for her unfailing enthusiasm and help in collecting most of the data; Kim Hardacker, Ryan Comber, John Borden,
Morgan Jones, and Nicole Jeans-Williams for their help in the field; rny parents for their help and encouragement; Lee Humble for his help starting this project; George Argus and Anna Roberts for help with willow identification; Del Meidinger for allowing me access to the dimate data; lan
Bercovitz for his help with PROC MIXED; and John Borden, Alton Harestad and Lee Humble for review of this manuscript.
This research was supported by the Natural Sciences and Engineering Research Council of
Canada, the Canadian Forest Sewice, Forest Renewal B.C., Ainsworth Lumber Co. Ltd., B.C.
Hydro Power Authority, Bugbusters Pest Management Inc., Canadian Forest Products Ltd.,
Crestbrook Forest lndustries Ltd., Finlay Forest lndustries Inc., Gorrnan Bros. Ltd,, International
Forest Products Ltd., Lignum Ltd., Manning Oiversified Forest Products Ltd., MB Research,
Northwood Pulp and Timber ttd., Pacific Forest Products Ltd., Phero Tech Inc., Riverside Forest
Products Ltd., Slocan Forest Products Ltd., TimberWest Ltd,, Tolko lndustries Ltd., Weldwood of
Canada Ltd., West Fraser Mills Ltd., Western Forest Products Ltd., Weyerhaeuser Canada Ltd. Table of Contents
.i Approval ...... 11 Abstract ...... iii Acknowledgements ...... v .. List of Tables ...... VII List of Figures ...... ix Introduction Materials and Methods ...... m...... m...... m.mmm...... mm...10 SELECTION OF SAMPLING UNITS ...... 10 SAMPLINGTREES ...... 15 SALIXIDENTIFICATION ...... 16 STATISTICALANALYSES ...... 17 Results and Discussion ...... 21 DISTRIBUTION AND ABUNDANCE ...... S...... 2f GEOGRAPHICRANGE ...... 21 EFFECTOF BIOGEOCLIMATIC SUBZONE ON THE PROPORTION OF ArrACKED TREES ...... 24 RELATIONSHIPBETWEEN THE PREVALENCE OF ArrACKED TREES AND MEVIL ABUNDANCE ...... 30 INFESTATION DYNAMICS AND IMPACT ...... 33 HOST PREFERENCE ...... 33 DlFFERENCES BETWEN ATTACKED AND AITACK-FREE TREES ...... 35 Size related factors ...... 35 Dead wood ...... 37 Stem breakage ...... 42 WITHIN-TREE DISTRIBUTION OF C. UPATHl ...... 45 Conclusions ...... m..mm.m..mm..mmm.m...... m..m...m...m...... mm52 Appendix ...... 57 References Cited ...... m...m...... mm..m...... 76 List of Tables
'able 1. Biogeoclirnatic description, sampling date, and coordinates of the 45 locations in this study in decreasing order of mean annual temperature ("C). Latitude and longitude are from the most central of the thrw possible sites.
Table 2. Components of regression equations used to predict the proportion of attacked trees in any biogeocfimatic subzone. The intercepts and cfirnate variables are tested with the null hypothesis that they, or their modifying parameters, are equal to zero. Residuals are tested against the null hypothesis that they are nomally distributed. See text for explanation of mode1 components.
Table 3. Results of correlation analysis between the mean proportions of trees with attack and dimatic factors.
Table 4. Ranked percentages of attack by C. lapathi on willow in various taxa. Some species presented in groups because of inability to distinguish benHeen specirnens collected. Othen pooled because of taxonornic affinity within a section. Sarnples were excluded if species could not be determined.
Table 5. Comparison between attacked and attack-free willows with respect to 14 rneasured characteristics. Values pooled for each site so that each site with both attacked and attack-free trees is a replicate.
Table 6. Ranked summaries of causes of stem death in willows assessed by visual observations in the field, comparing stems attacked by C. lapsthi with attack-free stems.
Table 7. Predicted proportions and confidence and prediction intewals for Model 1 (TMO) in order of decreasing predicted proportion. 58
Table 8. Predicted proportions and confidence and prediction intervals for Mode1 1 (W0) in alphabetical order. 61
Table 9. Predicted proportions and confidence and ~dictionintewals for Mode12 (MAT, NFFD, €LE) in order of decreasing predicted proportion. 64
Table 10. Predicted proportions and confidence and predicüon intewals for Mode! 2 (MAT, NFFD, ELE) in alphabetical order. 67
vii Table 11. Predicted proportions and confidence and ptediction intervals for Mode13 (THO, MTWM, DD>5) in order of decreasing predicted proportion. 70
Table 12. Predicted proportions and confidence and prediction intervals for Model 3 (T>lO, MTWM, DD>5) in alphabetid order. 73
------.- - - -
viii List of Figures
Figure 1. Photographs of preserved Cryptorhynchus lapathi larvae (A), preserved pupae (8) with ventral (left) and dorsal (right) views, and a live adult (C).
Figure 2. Damage by C. lapathion stems of Salix spp. showing stem breakage (A), abundant frass and adventitious branch formation (B), and dead stem 'flags' in an attacked tree (C).
Figure 3. Schematic diagram of sampling protocol using one biogeoclimatic zone and subzone as an example. See Table 1 for explanation of zone and subzone symbols.
Figure 4, Map of B.C. showing both the locations sampled in 1997-1998, in which attack by C, lapathi was present (solid blue circles) or not found (red stars) and the known distribution of C. lapathi in 1963 according to the Forest lnsect and Disease Survey data summarized by J.W.E. Harris (1964) (green shaded area). Numbers beside the stars refer to the following locations, biogeoclimatic zones and subzones: 1) Nadina Lake, ESSFmc; 2) Blunt River, ESSFmc; 3) Foxy Lake, ESSFmc; 4) North Ling Creek, SBSmc; 5) Dokie Creek, SBSwk; 6) Bowron Lake, ICHmk; and 7) Pimainus Lakes, ESSFxc.
Figure 5. Proportions of trees attacked by C. lapathi in biogeoclimatic zones and subzones in B.C. Data presented in decreasing order. Standard error bars with the sarne letters are not significantly different, LSMEANS, P ~0.05.Asterisks indicate subzones where at least one location lacked attack.
Figure 6. Regression analysis between the predicted and actual proportions of attacked trees for Models 1 to 3 (Table 2).
Figure 7. Relationships between the mean attack intensity score for attacked trees, or the number of current-year insects attacking trees, and the proportion of trees with attack. Each point represents one location.
Figure 8. Relationships for sites (left) and 15 biogeoclimatic subzones (right) between the proportion of dead wood by basal area for attacked (top) and attack-free (bottom) trees and the proportion of trees with C. lapathiattack. Not ail sites or subzones had attacked or attack-free trees, thus n varies. Bars on subzone graphs indicate S.E. Figure 9. Relationship between the volume of stem missing due to C. lapathi galleries as calculated by water displacernent and the diameter of stems at the point of breakage. 90th volume and diameter log transformed prior to regression analysis. 43
Figure 10. Frequency distributions of C. lapathi- and naturallycaused breaks in relation to diameter of the stem at the break point and length of stem from the root collar to the break point. 46
Figure 11. Frequency distributions of stem lengths and basal diameters. comparing all stems sampled to C. lapathi-attackedstems. 48
Figure 12. Relationship between the proportion of trees attacked by C. lapathi in each site and the ratio of attacked to 'large' stems >17 mm basal diameter. 50
Figure 13. Frequency distribution of lapathi range along the length of Salix stems. C. attack 53 Introduction
The poplar and willow borer, Cryptorhynchus iapathi (l.)(Coleoptera: Curculionidae:
Cryptorhynchinae) (=Sternochetus lapathi (L. ), =Cryptonhynchus lapathi (L .)), is an exotic weevil from Eurasia which attacks a wide selection of willows and poplars. It has been present in British
Columbia for >70 years (Harris and Coppel 1967).
The life cyde cm take 1 to 2 years, even within the same tree and among individuals of the sarne generation (Smith and Stott 1964). All lifestages are capable of overwintering (Chittenden
1904; Magerstein 1931; J.W.E. Harris 1964; Smith and Stott 1964). The eggs are creamy white, oval and ca. 1 mm long (J.W.E. Harris l964), and are laid in punctures made by the fernale near branch axils, buds or wounds, especially nearer the base of the stems, but also high in the crown of large-diameter trees or under a soi1 or moss layer. Larvae (Figure la) are C-shaped and legless, creamy white with a reddish brown head capsule, and are <1 .O to >10.0 mm long, length depending on instar (J.W.E. Harris 1964). 11 is unclear whether there are six (E.J. Harris 1959;
J.W .E. Harris 1964), five (Szalay-Mamsd 1962; Safranyik l963), or even four (Zivojnovie 1962) instars. Larvae mine in the host stem, at first in a girdling fashion in the phloem, then tunneling into the woody xylem for approximateiy 6 cm (J.W.E. Harris 1964). The gallery can extend up or down the stem, sometimes reversing direction to forrn a J-shape but occasionally can be a shallow pit excôvated under the bark instead of a long tunnel. Pupation occurs at the terminus of the gallery. Pupae (Figure 1b) are creamy colored but begin to darken as they age; the eyes darken first. Adults (Figure lc) are 0.5 - >1 cm long, and densely covered in grey-white to pink sales. The long rostrum can be tucked inlo a ventral groove in the prothorax. The legs are relatively long; the antennae are clubbed and elbowed.
The poplar and willow borer was first recorded in North America at Williamsbridge, New York
City in 1882 (Jeulich 1887). It spread rapidly westward in infested nursery stock from New York to North Dakota in 1904 (Washbum 1904), and in 1931, to Oregon (Chamberlin t 932). The
weevil was reported at three separate Toronto locations in 1906, suggesting an introduction to Figure 1. Photographs of preserved Cryptorhynchus Iapathi lawae (A), presewed pupae (6) with ventral (left) and dorsal (right) views, and a Iive adult (C).
Canada some time earlier (Caesar 1916). The first British Columbia record was at Vernon in
1923 (Harris and Coppel 1967).
Salix and Populus spp. are the preferred hosts of C. lapathi in North America, but in Europe the weevil also occasionally attacks Ainus spp., and rarely Betula spp. The known hosts
(Webster 1901; McC. Callan 1939; Schoene 1 goïa, l9O7b; Caesar 1916; Matheson 1917;
Houser 191 8; Strojny 1954; Zivojnovii and Tomii 1956; Szalay-Marzs6 1962; Froiland 1962;
J.W.E. Harris 1964; Smith and Stott 1964; Dafauce 1976; Dafauce and Cadahia 1977; Li et al.
1981; Noh et al. 1994) are listed below by their currently recugnized names (Kartesz 1994, Tutin et al. 1993), their synonyms (in parentheses), and, if different from above, as they were cited in the iiterature ln square brackets]:
Alnus glutinosa (L. ) Gaertn. [A. glutinosa, A. glutinosa Willd.] A. incana (L.) Moench [A. incana L., A. incana Moench, A. incana Willd., A. incana, A. incarna'] A. incana ssp. tenuifolia (Nutt.) Breitung (=A. tenuifolia Nutt.), (A. tenuifolia] A. viddis (Viii.) Lam & DC. [A. vinais DC., A. vin'dis] A. vMis ssp. sinuata (Regel) A 8 0.LBve (=A. crispa ssp. sinuata (Regel) HultBn, =A. sinuata (Regel) Rydb.), [A. crispa ssp. sinuata, A. sinusta'] Betuia nigra L. [B. ni ra] 8. papydfera Marsh. B [white birch] B. pendula Roth [B. pendula] B. pubescens Ehrh. [B. pubescens] B. pumila L. [B. pumiia] Populus alba I.(=P. alba var. bolleana Lauche), [P. alba, P. albs cv. bolleana Lauche] P. balsamifera L. [P. balsamifera] P. balsamifera L. ssp. balsamifera (=P. baisamifera var. candicans (Ait.) Gray, =P. balsamifera var. subconlata Hylander, =P. candicans Ait., =P. tacamahaca P. Mill.), [P. balsamifera var. candicans Gray, P. candicans, P. tacamahaca] P. balsamifera L. ssp. trichocatpa (Torrey 8 Gray ex Hook) Brayshaw (=P.irichocarpa Toney & Gray), [P. tnchocarpa] P. x berolinensis Dipp. [P. bemlinensis Dipp.] P. x canadensis Moench (=P. x euramericana (Dode) Guiner), [P. canadensis Moench, P. canadensis, P. x canadensis, P. canadiensis'. P. eummencan8 Guiner, P. x eurameticana] P. deltoides 8artr. ex Marsh. [P. deltoides Bartr., P. deltoid8~Marsh., P. deltoides] P. deltoides ss p. monilifera (Ait. ) Eckenwalder (=P. monilifen Ait. ), [P. monilifem] P. x generosa Henry [P. genema, P. x generosa] P. x jackii Sarg. (=P. x gileadensis Rouleau), [P. x gileadensis] P. nigm L. [P. nigra] [P. pseudo-simonil Kitag] [P. robusta7 P. simonii Carr. [P. simonid P. trernula L. [P. tremula] P. tremula ssp. davidiana (Dode) Hultdn (P. davidi8na5) P. tremuloides6 Michx. Pyms communis7 L. [Pirus communisl, pear] ~urnex'spp.
Salix acutifoliaQWilld . [S. acutifolia] S. alba L. [S. alba. S. aurea'y S. alba L. var. caerulea (Sm.) Sm. (=S. alba var. caerulea Sm.), [S. alba var. caerulea] S. alba L. var. vitellina (L.) Stokes [S. alba var. vitellina, S. vitellinaj S. amygda10ides~Anderss.[S. amygdaloides] S. arbusculoides Anderss. (=S. acutifolia auct. non Hook), [S. acutifolia Willd., S. acutifolia] S. babylonica L. (S. babylonica. S. babylonica Toum., S. babylonica ~owm.'] S. bebbiana Sarg. (=S. bebbiana var. permstrafa (Rydb.) Sneid.), [S. bebbiana var. bebbiana] S. caprea L. [S. caprea, S. caproea', S. cupreal] [S. cannabina'. "1 S. cinerea L. [S. cinerea, S. cinea', S. rnultiner~is'~] S. cordata Michx. or S. eriacephala Michx. [S. cordata] S. daphnoides Vill . [S. daphnoides] S. discolor Mu h 1. S. eriocephala Michx. (=S. cordata Muhl., non Michx.), [S. cofdata, S. amerkana Hort., S. amencana] S. eriocephala Michx. or S. cordata Michx. [S. cordata] S. exigua Nutt. (=S. interior Rowlee, =S. interior var. pedicellata (Anders.) Ball) S. fragilis L. [S. fragilis] S. lucida Muhl. [S. lucida] S. rnyrtillifolia Anderss . S. niga Marsh. S. pentandra L. [S. pentandra] S. petiolaris Sm. S. planifolia Pursh S. planifolia ssp. planifolia [S. planifolia Punh var. planifoia] S. purpurea L. [S. purpurea] S. x nrbens Schrank (=S. x vindis Fr.), [S. vinüis] S. scouleriana Barr. ex Hook [S. scouleriana Barr.] S. sekea Marsh. [S. sericeal [S. sabina'. '7 S. triandra L. (=S. amygdalina L.), [S. triandra, S. amygdalina] S. viminalis L. [S. viminalis]
' Probable spelling enor. Garbutt and Hafris (1994) report two incidences of C. lapethi attack on white birch. Cannot find reference to this spp. 'Cannot find current reference, but P. x robusta Dode was mcognired as a hybrid in Prain (1908). ' Cannot find curent reference to this spedes, but P. davidiana is a synoriym aCCOrding to Brenen (1981 ). Only 2 records: Cosens (191 2) and Garbutt and Harris (1994). ' Only one record of attack found in a mit tree (Ritzema-Bo6 1918); hovuever, there am several records of adulîs feeding on fruits and nu@ (Pettit 1925). 'These have likely been ated incmdly as hosts; however, adults could feed on them. Unnaeus (7758) found the wwvil on tapathurn (=sonel) or dock plants, Rumex spp., and thus named aie weevil 'laptht. @ S. acutilblia Willd. is a European to west Asian spedes; S. atnygdaloides Anderss. 1s an American species, ofhn incorrecîiy called S. acutilblia (George Argus, Memckville, Ontario, Canada, pen.comm.). 'O According to Jackson (1895) this is a synonyrn of S. al&. " Cannot find refererice to this sp. "This is a synonym of S. cinema L according to Jackson (1895), but has also been used to describe S. jntegra Thunb. (G. Argus, pers. comrn.),Mich is wmtntly recognizd as S. integra Thunb. ex Murray (Davies and Uoyd 1Wl), and in oie past was a synonyrn of S. nepens L (Jackson 1895). '' Cannot and referenœ to this sp., but if misspelled could be S. x sobn'na White (Jadwwi and Ouand 1W), an unknomi synonyrn. or cwld be S. semtine, vuhich can refer to either S. whinalis or S. tn'endm depending if the aulhodty is Pal!. Reise or Schur, raspecti~~ly(Jadrson 1985). 5 Mining by C. lapathi larvae in the phloem and wood severely weakens the stem and increases its susceptibility to breakage (Figure 2a). Production of adventitious shoots often occurs in or below damaged areas (Figure 2b). Small-diameter stems can be completely girdled and killed. In late summer attacked and broken branches with dried, red leaves are easily seen
(Figure 2c). Feeding by adults can lead to indirect damage in basket willow, causing the tips of young, vigorously growing shoots to snap off (Munro 1974; Ludwigs and Schmidt 1925; Szalay-
Marrso 1962; Smith and Stott 1964). This in turn causes the proximal portion of the stem to produce numerous secondary shoots which are unfavorabie for manufacturing baskets.
In Europe, basket and cricket bat willow beds attacked by C. lapathi are greatly debilitated, possibly because C. lapathi creates infection courts for fungal pâthogens in the bole (Lindeijer
1932; Smith and Stott 1964; Abebe and Hart 1989). Although this issue is far from clear (McC.
Callan 1939; Gremmen and de Kam l982), Smith and Stott (1964) considered weevil damage to forecast impending willow bed degeneration.
In China, attempts to breed weevil-resistant poplar trees with superior growth qualities have been undertaken (Gao et al. 1991). The weevil is considered a primary Pest of young hybrid poplar plantings in ltaly (Gianni Allegro, lstituto di Sperimentazione per la Pioppicoltura, Casale
Monferrato, Italy, pers. comrn.). Numerous other countries also report sorne level of C. lapathi impact, e.g., Sweden (Tullgren 1918; Kangas 1942), the United Kingdom (Munro 1914; Fryer
1917; Smith and Stott 1964; Neenan and Kennedy 1989), Poland (Kalandra 1948; Strojny 1954),
Hungary (Szafay-Mans6 l962), Croatia (Jodal 1987), Czechoslovakia (Magerstein 1928, 1931,
1932, 1940; Nejedly l938), Germany (Ludwigs and Schmidt l925), France (Cldment 1916; Attard
1978,1979), Canada (Caesar 1916; Boisvert 1926), and the U.S.A. (Matheson 1915; Froiland t 962; Sanders and Fracker 1916; Primm 1918; E.J. Harris 1959).
In North America, weevil-susceptible species of poplar and willow have been of limited ecunomic importance, but are important ecologically, e.g., as biowse for mammals such as mwse or beaver and in riparian areas, helping to stabilize soil, control water temperature and provide nutrient inputs. The importance of these species is rapidly changing. Native poplar and Figure 2. Oamage by C. lapsthi on stems of Salix spp. showing stem breakage (A), abundant frass and adventitious branch formation (B), and dead stem 'flags' in an attacked tree (C). willow whips have been planted in B.C. for stream bank stabilization and to control soil erosion
(White 1997). In Sweden, willow beds are being tested to determine if they can improve the quality of ground water draining from agricultural lands, and as a biofilter of waste water and sludge by accumulating heavy metals and absorbing excess nutrients (Christersson and
Sennerby-Forsse 1994). In Vernon, B.C., municipal effluent has been spread over hybrid poplar plantations (Carlson 1992). Because of their rapid growth rates and ability to coppice. poplar and willow are amenable to production of biomass for pulp and biothermal energy (Christersson and
Sennerby-Forsse 1994; Culshaw and Stokes 1995; Brown 1999; Turner 1999). Energy production from biomass is sustainable and CO2-neutrai. In Australia, carbon-forestry is expanding to provide energy, ethanol, and carbon for steel making, silicon smelting and the production of activated carbon filters (David Brand, Executive General Manager, State Forests of
New South Wales, Pennant Hills, Australia, pers. comm.). There is increasing actual and
potential use of hybrid poplar for the production of pulp, lightweight construction materials,
paneling, moldings, and furniture manufacturing (Carlson and Berger 1998). Finally, poplar and
willow are valuable as ornamental trees where darnage is undesirable (E.J. Harris 1959; 0.
DeJong, Misty Meadows Nursery, Surrey, B.C., pers. comm.).
The rnajority of published research on C. iapathi examines, at least in part, host resistance
or chernical, physical or biological control methods (e.g., E.J. Harris 1959; J .W.€. Harris 1964;
Harris and Coppel 1967; Cavalcaselle 1975; Lou et al. 1983; Cavalcaselle and de Bellis 1983;
Cavalcaselle and Deseo 1984; Jodal 1987; Lapietra and Allegro 1987; Allegro 1989, 1990a,
1990b; Noh et al. 1994). Fewer studies have focussed on the ecology of C. lepathi.
I wnducted a survey of C. lapathi to assess its prevalence and impact on native Salk spp.
across the mainland of B.C. The weevil is capable of fiight (Szalay-Marzs6 1962; Smith and Stott
1964), but dispersal across ttie province has not been studied. Although C. lapathi exhibits clonal
prefetences in poplar plantations and among some willows (Caesar 1916; Szalay-Mans6 1962;
Dafauce 1976; Dafauce and Cadahia 1977), such information is not known for Salfx spp. in B.C.
My objectives were: 1. to determine the range and incidence of C. lapathi across B.C.;
2. to determine if there is a significant interaction between the proportion of trees with
C. lapathi attack and biogeoclirnatic subzone or site factors;
3. to detemine which native Salix spp. are susceptible to C. lapathi attack and if there
is any evidence of host preference;
4. to describe and compare the characteristics of attacked and attack-free trees to
eiucidate how native wiilow populations have been affected by C. lapathi; and
5. to describe the within-tree distribution of C. lapathi attack.
Materials and Methods
A systematic sarnpling protocol was followed (Figure 3). Within each of five biogeociimatic zones
in B.C. (Meidinger and Pojar 1991), three subzones were chosen to maximize variation between
available rnoisture regimes, i.e., one dry or very dry subzone, one moist subzone, and one wet or
very wet subzone. Each subzone was sampled at three locations (Table l), each road-
accessible with 250 km between them. Because suitable locations for the wettest subzones
could not be found in the lnterior Douglas Fir (IDF)zone, the very dry hot (xh), dry cool (dk), and
wet warm (ww) subzones were chosen. Three sites were chosen at each location to increase the
likelihood of encountering different Salix spp. Sites differed by extent andlor type of disturbance
andlor water abundance, andor light competition, but alwere within an approximate 3-km radius.
At each site, five willow trees (or clumps) were sampled intensively, and 20 additional trees were
assessed only for presencelabsence of attack. The total possible number (675) of trees were
intensively sampled, but only 2,685 (not 2,700) trees were additionally sampled because some 10 Figure 3. Schematic diagram of sampling protocol using one biogeoclimatic zone and subzorie as an example. See Table 1 for expfanation of zone and subtone syrnbols. Bioaeoclimatic Zones + CWH ICH IDF SES ESSF
Locations Marble 1 50 Mile Shatford + Canyon House Creek (2 50 km apart)
-Sites + wet site, dry site, another site, (s6 km apart) creek side open, sunny slope road side, dense edge
25 trees 25 trees 25 trees Table 1. Biogeoclimatic description, sampling date, and coordinates of the 45 locations in this study in decrearing order of mean annual temperature ("C). Latitude and longitude are from the most central of the three possible sites.
Biogeoclimatic zone, wi th subzone, MAT", and location Date Latitude Longitude lnterior Douglas Fir wet wan (IDFww), 9.4OC
Ainslie-Mowhokam Creeks 21 Aug.-98 50" 00.125' N 121O 28.644' W Seton Portage 9-1 3 Sept.-97, 25 May-98 50" 43.453' N 122" 15.655' W Twin Creek 22 Aug.-98 50°14.991'N 122O29.512'W
Coastal Western Hemlock very wet maritime (CWHvm), 8.2OC Clayton Falls Gamet Creek Hirsch Creek
Coastal Western Hemlock dry subrnantirne (CWHds), 7.8OC McGillivray Creek II 24-26 May-98 50" 37.647' N 122" 29.443' W Snootli Creek 10 Auge-98 52" 22.479' N 126" 37.052' W Yale 22-23 Sept.-97'23 May-98 49" 34,630' N 121 O 25.514' W
Inlerior Cedar Hemlock dry wann (ICHdw), 7.3OC Goat River Needles Robson lnterior Douglas Fir very dry hot (IDFwh), 6.5OC Lillooet Princeton Whiteman Creek
Coastal Western Hemlock moist submaritime (CWHms), 5.8OC Arnerican Creek Casper Creek Larso Bay lnterior Cedar Hemlock moist ml (ICHmk), 4.5% Blaeberry River Bowron ~akd South Barrière Lake Table 1 con?
Interior Douglas Fir dry cool (IDFdk), 3.g°C
Marble Canyon 30 Apr., 1 May-98 50" 51.51 5' N 121 a 46.374' W 150 Mile House 11 -1 2 AU^ .-98 52" 06.033' N 121" 53.788' W Shatford Cteek 30-31 JUW, 16 Aug.-98 49" 26.760' N 119" 49.135' W lnterior Cedar Hemlock very wet cool (ICHvk), 3.8OC Chappel Creek Perry River Upper Fraser
Sub-Boreal Spruce dry warm (SBSdw), 3.2OC Bouchie Lake Ruth Lake Saxton Lake
Sub-Boreal Spruce wet cool (SBSwk), 2.1°C Dokie creekb Kangaroo Creek Tacheeda Lakes
Engelmann Spruce Subalpine Fir wet mild (ESSFwm), 2.0°C McGillivray Creek I 15-16 Sept.-97'24 May-98 50" 36.587' N 122" 33.383' W Sanca Creek 23-24 dune-98 49O20.413'N 116°37.530'W Tularneen River 19-20 Aug.-98 49" 26.065' N 121O 00.778' W
Engelmann Spruce Subalpine Fir very dry cold (ESSFxc), 1.5OC Apex Mountain The Greystokes Pimainus Lakesb
Sub-Boreal Spruce rnoist cold (SBSmc), 1.O°C Arctic Lake 3 Aug.098 53" 40.375' N 123" 50.639' W Moffat Lake 25-26 Aug.-97, 12 Aue.-98 52" 07.820' N 121" 13.518' W North Ling creek8 26 July-98 54" 22.093' N 125" 36.385' W
Engelmann Spruce Subalpine Fir rnoist cold (ESSFmc), -0.7OC Hunt ~ive* Foxy Lakeb Nadina Lakeb
a = mean annual temperature (OC) = no attacked trees were fou^ at mis location sites did not contain 25 trees. Sarnpling was partially completed at five locations in 1997, and the remainder of the locations were sarnpled in the summer of 1998.
SAMPLINGTREES
The species of willow sampled depended on the species growing in any given site. All trees sampled had at least one stem 117 mm basal diameter, a lirnit set to ensure that the tree could sustain C. lapathi attack. Although most willows would be considered shrubs because of their rnulti-stemmed nature (Brayshaw 1996b), they are often trw-sized in stature (~2m) (Brayshaw
1996b). Since the mean maximum height of ail trees sampled was 2.9 m, I feel the use of 'tree' to refer to an individual plant is acceptable. The first intensively sampled tree was chosen randomly, using either a random compass bearing or a randomly determined distance depending on whether it was growing in a patchy, circular or linear environment. Trees were excluded from this selection procedure only if they were too small, subrnerged in deep water, or contained active bird (and in one case red ant) nests. Sequentially, the next ctosest trees were intensively sampled. The 20 additional trees were nearest neighbours of the five intensively sampled trees.
Where it was impossible to identify an individual tree (e.g., clonal S. exigua or S. melanopsis, or old, sprawling layered clumps of S. dmmmondiana), stems rooting within a 1 m2 patch were measured as a unit. The next closest, but distinct, patches were then sampled in a similar manner. The approximate dimensions of the plot containing al1 25 trees were recorded.
For the first five trees, the basal diameters, vertical heights, and lengths were recorded for the stems (originating at the mot crown), adventitious branches (resulting after the main stem
died) and codorninant branches. Diameters were measured with calipers or a diarneter tape, and
heights using a calibrated telescoping pole. The stem was classified as alive or dead. If boring
damage had occurred, the length of damaged area along the stem and the diameters of the
highest and lowest attack points for both oId and current attack were recorded. The number of C.
lapathi galleries containing current-year insects was determined by dissection. If a stem was
broken due to C. lapathidamage or any other cause, the diameter and length of the stem just
15 below the break point was recorded. If the break was C. lapathi-induced, as much as possible of the broken portion plus some stem distal andlor proximal to the break were returned to the laboratory and the volume missing due to C. lapathi galleries was determined by water displacement. The broken stem portions with a minimum amount of stem tissue not involved in the break were sealed in waterproof plastic, placed in a volumetric cylinder and their volume estimated. The broken stem portions were then opened to rernove al1 the C. lapathi frass, presoaked in water, and again measured volurnetricatly, the difference between the two volumes estimating the volume removed by C. lapathi. The length of C. lapathi galleries was estimated while removing frass and the size of the broken portion was measured with calipers (diameter) and a ruler (length). When I anticipated that it would be too time consuming to conduct the intensive field measurements on a tree, usually because it had numerous stems, I would sub- sample a fraction of the stems. The remaining stems were simply noted as being alive or dead and whether they contained current, old or both types of C. lapathi attack.
Al125 trees at each site were scored by attack intensity (O = none; 1 = attack present, but not obvious; 2 = attack readily visible but moderate; 3 = attack heavy on al1 stems) and whether the attack was current, old or both.
A leafy, and if possible catkin-bearing, branch sample was removed from each tree, and identified using published keys (Argus 1991; Brayshaw 1996a, 1996b) or INTKEY (Argus 1999), a computerized, interactive key provided by George Argus, Merrickville, Ontario, Canada. The species reported in this paper are in agreement with Kartesz (1994). A subset of specirnens was compared with herbarium specimens hmthe University of British Columbia. Some similar species could not always be separated. For example, S. scoulerians appears alone and in the S. scou/etfana/bebbiana group because vegetative specimens collected early in the season were difficult to distinguish from S. bebbiana. Sa/& barclayi and S. pseudomonticoI8 were grouped together because it was very difficult to distinguish between them without catkins. Similarly, S.
16 bebbiana and S. giauca were also grouped. Extremely problematic specimens were taken to
George Argus and Anna Roberts, Williams Lake, B.C., Canada, for identification during a willow workshop they hosted. A total of 26 specimens, most of which lacked leaves and catkins. remain unidentified.
STATISTICALANALYSES
Data were analyzed by both parametric and non-pararnetric tests (Jones 1984; Zar 1984;
Day and Quinn 1989; Daniel 1995) using the SAS statistical package (SAS lnstitute 1990) and in some instances. e.g.. for paired t-tests. using the analysis tools package in ~icrosoft~Excel
(~icrosoft@Corporation 1995). In ail cases a = 0.05.
The mean proportions of attacked trees for the nine sites in each of 15 biogeoclimatic subzones were analyzed by PROC MIXED, a rnodified ANOVA procedure, which can accommodate both random and fixed effects in a nested design framework; differences between subzones were determined using a Bonferroni adjustment with LSMEANS, a modified least significant difference procedure (SAS lnstitute t 990). Pearson Correlation Coefficients were calculated between the mean proportion of attacked trees for each biogeoclirnatic subzone and the corresponding means for 19 ciimatic parameters (provided by 0.Meidinger, Research
Branch, B.C. Forest Service) as follows:
DD
The influence of site factors on the incidence of attacked trees was analyred by chi-square tests. Sites were classed by the percent of attacked trees (>75%, >25% to s 75%, or ~25%)~and light availability (open grown trees, willow closed canopy, willow partially shaded by dominant canopy, or willow continuously shaded by dominant canopy) or water availability (high, intermediate or low). Correlation analysis was used to determine if any relationship occurred between host density and the proportion of attacked trees within sites.
The mean attack intensity scores within each location were compared to the proportions of trees attacked by linear regression (Zar 1984). Similarly, regression analysis was used to compare the relationship between the proportions of attacked trees within each location and the numbers of weevils (larvae, pupae and adults) recovered (a second measure of attack intensity).
The numbers of weevils per attacked tree were transformeci by loglo(x+l) to correct for non- normality (Zar 1984). Because there were few attacked trees at each site (~5)~insect numbers were pooled by location. Data from McGillivray Creek, Yale, Gamet Creek, Marble Canyon and
Seton Portage were deleted from the analysis because stems were dissected too early or too late
in the season to recover C. lapathi.
The numbers of attacked willows of different species (some species grouped because of
inability to separate, others pooled by taxonomic affinity into sections) were compareci by chi-
square analysis. To allow for differences that could have been caused by climat0 andlor weevil
presence in a location, expected values were calculateâ separately by location, and then
summed for each species, group or section. fable 2. Components of regression equationi uied to predict the proportion of attacked trees in any biogeoclimatic subzone. The intetcepts and climate variables are tested (t- test) with the nuIl hypothesis that they, or their modifying parameters, are equal to zero. Residuals are tested against the nuIl hypotheiis that they are norrnally distributed (W- statistic). See text for explanatiorr of modal components.
Model to predict proportion Mode, Test statistic of attacked willow trees
T>10 lntercept Residuals
MAT NFFD ELE lntercept Residuals
T>lO MTWM DD>5 lntercept Residuals Attacked and attack-free trees were compared with respect to 14 rneasured characteristics including only sites where both types of tree occuned. Values for each characteristic were pooled for attacked and attack-free trees within a site, creating one replicate per site.
Comparisons of means employed paired t-tests, when the data were nonnally distributed or when removal of a single outlier resulted in normaîity. Otherwise I used a paired sign test based on the normal approximation of the binomial probability (P = 0.50) of seeing 'ktmany negative or positive observations given the total number of non-zero ditferences (SAS Institute 1990; Daniel 1995).
Regression analysis was used to determine the relationship between the proportion of dead wood and the proportion of attacked trees in sites and subzones. The volume and proportional volume of stem missing frorn broken portions was regressed against the diameter of the break to determine the amount of damage needed for stems of certain sizes to break. In the former instance, both diameter and volume were transformed by log(x) (Zar 1984). 1 used chi-square analyses to compare the distributions of naturally- and C. lapathi-caused breaks by both diameter and length at which the break occurred.
Similarly, chi-square analyses were used to compare the frequency distributions of C. lapathi-attacked stems to the entire population of sampled stems with respect to length and basal diameter. All cornparisons of attacked and attack-free stems within attacked trees and the range of old and current-year attack within stems were done using the paired sign test, approximated by the normal distribution as above. tastly, for each site, the ratio of attacked stems to large stems
217 mm basal diameter was regressed against the proportion of ail trees attacked. The ll(x +
0.5)'" transformation was used to correct for non-normality (Zar 1984). Results and Discussion
DISTRIBUTION AND ABUNDANCE
GEOGRAPHICRANGE
The weevil was widespread across the province, but was not found in seven locations
(Figure 4). Although these locations tend to be cool, C. lapathi was found at other locations within the same biogeoclirnatic subzone with the exception of the three ESSFmc locations (Table
1, Figure 4). Its absence at North Ling Creek, Dokie Creek, Bowron Lake and Pimainus Lakes may indicate that it has not yet had the to colonize its complete potential range, perhaps because its progress has been slowed by climate. Its absence from the three ESSFmc locations probably reflects the cold climate (Table 1).
In comparison to the known distribution of C. lapathi in B.C. in 1963 (Figure 4), the weevil has at least doubled its range and has become newly established in the Williams Lake, Prince
George, and Bella Coola areas. Further extensions of the range rnight be disclosed by more extensive sampling. Because the Terrace population was quite isolated in 1963, combining an
intensive search for the weevil between Bella Coola, Terrace, the Lower Mainland and the interior
of the province with a study of lineages using molecular markers might disclose if the expanded
range is due to gradua1 dispersal or independent introductions.
The capacity of C. lapathi for flight and longdistance dispersal is unknown because
observations of fiight are so rare. Szalay-Mans&(1 962) observed directed flight from one willow
to another in Hungary. Smith and Stott (1964) report an incident of an adult escaping and fiying
in the laboratory and another instance when one flew into the house of a Salix grower in England,
in addition to frequent flights in crowded, caged conditions within a greenhouse- In B.C., J. H.
Borden (Dept. of Biological Sciences, Simon Fraser University, pers. comm.) obsewed active
flight at the University of Northem British Columbia campus in Prince George and the occasional
C. lapethi is found in multiple-funnel traps baited with ethanol (L. M. Humble, Pacifc Forestry
21 Figure 4. Map of B.C. showing both the locations samplad in lW?-l998, in which attack by C. Iapathi was present (solid blue circler) or not found (red stars) and the known distribution of C. lapaihi in 1963 according to the Forest Insect and Disuase Survey data summarized by J.W.E. Harris (1964) (green shadeâ area). Numbem baside the stars refer to the following locations, biogeoclirnatic zones and subzones: 1) Nadina Lake, ESSFrnc; 2) Blunt River, ESSFmc; 3) Folry Lake, ESSFrnc; 4) North Ling Creek, SBSmc; 5) Dokie Creek, SBSwk; 6) Bowron Lake, ICHmk; and 7) Pimainus Lakes, ESSFxc.
Centre, Canadian Forest Service, and R. L. Mclntosh, Dept. of Biological Sciences, Simon Fraser
University, pers. comm.). Thus, flight is possible, but it's importance in expfaining the large range expansion over 35 years (Figure 4) is unknown.
EFFECTOF BIOGEOCLIMATIC SUBZONE ON THE PROPORTION OF ArrACKED TREES
There were highly significant differences among biogeoclimatic zones, subzones, and locations with respect to the proportions of willows attacked by C. lapathi (F = 38.95, P <0.0001, ndflddf = 4/28; F = 1138, P <0.0001, ndflddf = 10128; F = 3.96, P <0.0001, ndflddf = 30160, respectively). Most importantly, the coldest subzones tended to have the lowest proportions of attacked trees. The ICI-lmk had a significantly lower proportion of attack than the 10 subzones with the highest proportions of attacked trees. The SBSwk. SBSmc and ESSFxc had proportions of attacked trees not significantly greater than in the ESSFmc, which had no attacked trees
(Figure 5).
Several climatic factors were significantly correlated to the proportion of attacked trees
(Table 3). Precipitation-related factors and extreme minimum temperature ("C) were not significantly correlated; however, al1 other factors, primarily measures of the warmth of the growing season, were significant (a = 0.05). Using some of these factors (Table 2), three final model equations are reported, each with different strengths (Figure 6). See Appendix for predicted proportions of attacked trees, with the 95% confidence and 95% prediction intervals calculated by each equation. AI1 models show declining incidence of C. lapathi-attacked trees with increasing severity of climate, suggesting that C. lapathi may soon approach the northem limit of its potential geographic range, at least in the interior of B.C. (Figure 4) where cold zones and subzones tend to occur (Meidinger and Pojar 1991).
Despite the striking ability of climatic factors to predict the expected proportion of attacked hees in a biogeoclimatic zone (Figure 6), there were absolutely no trends in light availability (X2 =
5.23, P = 0.51, df = 6). water availability (X2 = 3.79. P = 0.44. df = 4) or density (r = 0.0056, P =
0.949, n = 133) of willow trees that could account for differences in üie proportion of attacked 24 Figure 5. Ranked proportions of trees attacked by C. lrprthl in biogeocllmatlc zones and subzones in B.C. Bars with the same letten are not significantly different, LSMEANS, P Table 3. Results of correlation analysis between the mean proportions of trees with attack and climatic factors. Pearson Correlation Factors n Coefficient P Temperature-Related Factors T>10 15 0.89874 MTWM 15 0.86191 MAT 15 0.82820 EXT 14 0.80522 NMWS 14 -0.77733 DD>5 14 0.74482 DDcO 14 -0.70508 Tc0 15 -0.67484 €LE 15 -0.65342 MTCM 15 0.60764 FFP 14 0.55238 NFFD 14 0.55036 €NT 14 0.49472 Precipitation-Related Factors MWP 14 0.27082 MPWM 14 0.26950 MAS 14 -0.25761 MA? 14 0.2301 5 MPDM 14 0.14904 MSP 15 0.01 042 Figure 6. Regression analysis between the predicted and actual proportions of attackeâ trees for Models 1 to 3 (Table 2). MODEL 2: MAT, ELE, 8 NFFD y=0.848~ +0.088 ' ? =0.842 1 P ~0.0001 n = 14 Actual Proportion of Attacked Trees trees between sites. However, I observed several instances where it appeared that trees in warm sites were more frequently attacked than in cool sites within the same location. For example, one site at Moffat Lake, located along an epherneral creek in a clearcut, had attack, yet the forested site along the same creek had none. At Tacheeda Lake, an exposed clearcut had attack, but two partially shaded sites had no attack. Within site 3 at Saxton Lake, none of the shaded willows had attack, but trees exposed to the sunlight were attacked and had fiass at their bases. All of the above sites, and others where ! noticed similar trends, were in colder subzones, suggesting that differences in local distribution occur most frequently where temperatures may be approaching the minimum threshold for larval development. RELATIONSHIPBETWEEN THE PREVALENCE OF AlTACKED TREES AND WEEVIL ABUNDANCE The mean attack intensity scores for attacked trees were directly related to the proportions of trees attacked (Figure 7). Thus as more and more trees became attacked, the intensity of attack within a given tree also increased. Furthermore, the attack intensity as evidenced by the recovery of actual weevils, was also positively related to the proportion of trees attacked (Figure 7). Large numbers of attacked trees in an area have frequently been docurnetited, indicating that populations can also becorne very large. For example, White (1997) reported 91.4% of trees in a young cottonwood plantation with attack. ln some of my locations, 100% of the trees sampled had attack. Also, of the 1831 attacked durnps, only 9.9% lacked old attack, indicating that most trees are attacked repeatedly and relatively few attack-free neighbours are colonized every year. This conclusion is consistent with the finding that marked weevils in a Selrix bed demonstrated very little rnovement away from their capture point (Smith and Stott 1964). Figure 7. Relationships between the mean attack intmdty score for attacked trees, or the number of current-year insects attacking trws, and the proportion of trees with attack. Each point represents one location. ATTACK INTENSITY SCORE y = 1.050~+ 1.234 NUMBER OF CURRENT-YEAR INSECTS y = 1.865e0.M1" ? = 0.562. P I la= Un 1 1 1 1 1 O 02 O .4 O .6 O .8 1 Proportion of Trerr with Mack lNFESTAflON OYNAMICS AND lMPACT HOSTPREFERENCE Attack by C. lapathi was observed on rnany native Salix spp. (Table 4), and also on S. brachycarpa Nuttall individuals too small in basal diameter to be included in this study. Salix geyenana Andersson observed independently at the Malcolm Knapp Research Forest, University of British Columbia Research, Maple Ridge, B.C., also had attack. The observations for S. barclayiAndersson, S. brachycarpa, S. dnrmmondiana Barratt ex Hooker, S. geyenana, S. glauca L., S. hookeriana Barratt ex Hooker, S. melanopsis Nuttall, S. prolixa Andersson, S. pseudomonticola Bal1, S. pyrifolia Andersson and S. sikhensis Sanson ex Bongard are apparently new host records for C. lapathi. None of the seven clumps of S. commutata Bebb sampled was attacked, but it was found only in locations with little or no attack. Calculation of expected values for chi-square analysis by location, a more sensitive measure of weevil presence and abundance in an area than biogeoclimatic subzone, showed lack of evidence for host preference (Table 4). Had biogeoclimatic subzone been used as the basis for expected values, there is evidence of host preference (X2 = 23.86, P = 0.005, df = 9), but this is strongly influenced by the distribution of Salix spp. Specifically, S. commutata was found in the ESSFmc and ESSFxc; S. dmmmondiana in the ICHmk, SBSmc, ESSFxc, and ESSFmc; S. barclayi/pseudomonticola in the CWHms, ICHmk, SBSwk, SBSmc, ESSFxc, and ESSFmc; and S. pyn'folia in the SBSmc. Conversely, S. scoulefiana was found rnostly in locations with very high Ievels of attack. The lack of host preference indicates that native species as a whole are more or less equally vulnerable to the damage the weevil can inflict. Similady, high vulnerability of native species to exotic pests have been shown in other instances where CO-evolutionhas not occurred, e.g., North Arnerican soft pines and white pine blister rust, Cmnstiium ribicola 3.C. Fischer ex Rabh . (Ziller 1974). Table 4. Ranked percentages of attack by C. lapathi on willow in various taxa. Some species presented in groups because of inability to distinguish between specimens collected. Others pooled because of taxonomie affinity within a section. Samples were excludecl if species could not be determined. Taxonornic designation, with numbers of trees (clumps) Nurnber of trees Percent with C. in parentheses for species pooled by section sampled lapathi attacka Group S. scoulerianalbebbiana Section cinefella S. scouledana (248), S. hookedana (1 ) Section longifoliae S. exigua (2)8 S. melanopsis (7) S. lucida ssp. lasiandra (Bentham) E. Murray Group S. planifolialdiscolor Group S. bebbianalglauca Section haststae Grou p S. barclayi/pseudomonticola (56) S. pyrifolia (1 ) & S. cornmutata (7) a No significant difference between percents with attack. X2 = 9.85, df = 9. P = 0.363. To accowt for climatic (Figures 5 and 6) and locational (Figure 4) diffmces that could have influenced the percent attack. expected values for each species. group or section were calculated separately by location and then summed. However, host preference does exist. Inhibition and stimulation of oviposition have been linked to two unidentified substances isolated from resistant and susceptible Populus hybrids, respectively (Dafauce 1976; Dafauce and Cadahia 1977). Others have also shown resistance among poplar clones (Szontagh 1983, 1985; Jodal 1987; Noh et al. 1994). Caesar (1916) felt that Babylonian willows were attacked less frequently in Ontario than native species. In Hungary, the exotic species S. americana had more frequent and severe attack than S. cannabina, S. acutifolia and S. purpurea (Szalay-Mans6 1962) and this phenornenon is generally accepted as fact across Europe (Smith and Stott 1964). DIFFERENCESBETWEEN ATTACKED AND ATTACK-F REE TREES Size related factors Attacked trees were larger than nearby attack-free trees with respect to basal diameter of stems, stem length, maximum stem height, number of stems, number of stems 217 mm diam. and total basal area (Table 5). These results are similar to those of Safranyik (1963) who found significant positive correlations between the number of current infestations and tree height, diarneter at breast height (1.3 rn) and age. Thus as for conifer teminal weevils, Pissodes spp. (VanderSar 1977; Maclauchlan 1992), if C. lapathi has a choice, it prefers to attack large trees that could support many weevils. Alternatively, large trees may also be more apparent (Feeny 1976) than small trees, and have a higher probability of intercepting flying weevils. Large trees could also be older than small trees (Safranyik 1963), and exposed to attack for a longer period. On several instances I observed old, relatively large, attacked trees apparently acting as a source of weevils that then initiated attack on srnall trees. Mean height of al1 stems was not significantly different between attacked and attack-free trees (Table 51, perhaps surprising given that mean stem height and length for each clump were highly comtlated (r = 0.953, n=135, P < 0.0001). When small-diameter stems (47mm basal Table 5. Cornparison between attacked and attack-free willows with terpect to 14 measureâ characteristics. Values pooled for each site so that each site with both attacked and attack-free trees is a replicate. Attacked trees trees - - t or z Characteristic measured n (x+SE) (xî SE) valuea P stem basal diameter (mm) stem height (cm) stem height (cm) when basal diameter 2 17 mm stem length (cm), including curvatures max. vert. stem height (cm) no. stems no. stems with a basal diam. 217 mm basal area of multiple stems per tree (cm2) angle of stems from vertical (degrees) % dead basal area per tree % stems dead no. adventitious branches per stem no. of breaks per stem no. breaks per stem not associated with C. iapathi attack a z-value derived hmthe normal approximation of the binomial distribution for the paired sign test. diam.) were excluded, the difference in height between attacked and attack-free trees became even smaller. The fact that attacked trees had longer stems than attack-free trees, but the overall height is the same, rnay be because attacked trees have more broken stems lying close to the ground which would decrease height measurernents and keep length measurements constant. Attacked trees, being bushier than attack-free trees, may also have spread out from the central crown and therefore may have long stems, but be no higher than attack-free trees. Darnaged trees with broken stems may be more stressed and therefore more likely tu be attacked than undarnaged trees. The hypothesis that attacked trees have a more prostrate growth form than attack-free trees is consistent with a greater off-vertical angle for attacked trees (Table 5). Dead wood Attacked trees had a significantly higher proportion of dead basal area (calculated as the basal area of dead stems divided by the total basal area of a given tree, assuming stems were circular in cross-section) (Table 5). This measure underestimates the lethality of C. lapathi attack because many stems, classed as living, had a few stniggling adventitious shoots surviving, and were obviously moribund. Because attacked trees were larger than attack-free trees (Table 5), they may also be older and could have accumulated more dead wwd naturally. Visual assessment in the field determined that C. lapathi alone or in combination with a canker disease was the primary cause of stem death in 38.5% of attacked trees (Table 6). For C. lapathi to be accepted as the cause of stem death, attack had to be so heavy that translocation would have been impossible, directly girdling the stem or causing a severe basal break. The canker distinctly matched the description of Cytospora chtysospema (Pers.: Fr.) Fr. (Allen et al. 1996). In recently killed stems, the bark is orange with an unpleasant odor, and often has orange tendrils protruding through the bark. In long-dead stems, the bark easily falls away from the stem in long strips, and still has the holes made by the tendrils. The results demonstrate that: 1) C. lapathi does cause some stem death; 2) over half the dead stems had attack; and 3) canker plays an important role in stem death. If fwther observations indicate that C. lapalhi and canker occur more frequently together than independently, it could mean that C. lapafhieither vectors or Table 6. Ranked causes of stem death in willows assessed by visual observations in the field, camparing stems attacked by C. lapathi with attac k-free stems. Attacked stems Attack-free stems Cause of death % Cause of death % ------ unknown 22.7 unknown 39.3 C. lapathi attack 20.5 cankef 28.6 C. lapathi + can ke? 1 8.0 mechanical cuts 16.3 canke? 17.2 othe? 12.8 mechanical cuts 9.2 beaver 3.0 othe? 8.7 beaver 3.6 a probably Cytospora chrysospema 'includes such causes as rot, lightening, snow press, and pushing over by large fallen trees creates infection courts for the disease, or that the fungus weakens and predisposes the tree to C. lapathi attack. Wounding by C. lapathi has been irnplicated in facilitating entry of Septoria musiva Peck into hybrid poplar bark (Abebe and Hart 1989). The hypothesis that C. lapatii is responsible for high proportions of dead wood within a clump is supported by the significant positive relationships between weevil prevalence and the amount of dead wood in attacked trees, and the corresponding negative relationships (albeit weak) in attack-free trees (figure 8). If cuid subzones wi!h low levels of attacked trees also have low weevil populations within trees (Figure 7), then it follows that attacked trees in these areas would show less impact. Many investigators have concluded that C. lapaihi prefers stressed or weakened trees, so dead wood rnay increase attractiveness to C. fapathi, assurning trees with dead wood are perceived as stressed. Once attacked, stressed trees may even be Iess able to defend against further attack. Large trees could also be more attractive than small trees if they lack vigor. Harrison (191 5) noted that C. lapathi attacked S, cinerea that had been previously weakened by the willow scale, Chionaspis salicis Linnaeus. Alnus incana weakened by the pathogen Nectria cinnabanna (Tode ex Fr.) Fr. were attacked and killed by secondary insects including C. lapathi (Kangas 1942). Magerstein (1928) felt that dry sites had higher populations of C. lapathi than areas where there was adequate soi1 moisture, probably because trees in dry areas were drought stressed. Waterlogged or saline soils also weaken willow beds, increasing their susceptibility to C. lapathi attack (Szontagh 1983), although periodic fiooding may drown weevil infestations (Chittenden 1904; Nejedly 1938). Extremes of drainage stressed poplar plantations in Michigan, resulting in a high incidence of C. lapathi darnage (Woods et al. 1982). Magerstein (1931 ) also reported C. lapathi predominantly attacking healthy young willows. Where there was an adequate water table, willows in North Dakota were more tolerant of C. lspathi attack than those on dry sites (Froiland 1962). However, poplars growing on the richest soils were more heavily attacked than trees growing in poor soils (Attard 1978), and the rnost vigorous poplar clones under various irrigation regirnes were attacked most intensely (Dafauce 1976). Figure 8. Relationships for sites (left) and 15 biogeoclimatic subzones (right) between the proportion of dead wood by basal area for attacked (top) and attack-free (bottom) trees and the proportion of trees with C. lapalhi attack. Not al1 sites or rubtoner had attacked or attack-free trees, thus n varies. Bars on subzone gtaphs indicrte S.E. SITE BlOGEOCLlMATlC SUBZONE 0.5 1 ATTACKED TREES CATTACKED REES y = 0.499~+ 0.084 y = 0.294~+ 0.042 A 8 = 0.584 6 = 0.231 A 0.4 P <0.0001, n = 100 A A A P = 0.0015, n = 14 ATTACK-FREE TREES y = -0.205~+ 0.247 8 = 0.093 t P = 0.0029. n = 93 Proportion of Attacked Trees Only 1.8% of the 3,360 willow trees sampled were dead and, by visual estimation, at least half of these apparently died in conjunction with canopy closure. In a Black Hills, North Dakota, survey, Froiland (1962) found some sites, prirnarily dry, that appeared to be under significant weevil pressure, and willows in these areas were declining. However, the willows in the Black Hills were not under any apparent threat of extinction due to C. lapathi, and if Viere was adequate soi1 moisture, the impact was negligible. My observations agree witb those of Froiland (1962). Trees like S. scouleriana growing on dry hillsides in the interior of B.C. suffer the most severe damage. Formerly live stems, 210 rn tatl, have died back after attack so that the only living parts are adventitious branches. These trees usually have canker in them as well. Stem breakage Attacked trees had more breaks per stem, and more "natural" breaks per stem not associated with C. lapathi attack, than attack-free trees (Table 5). (Because C. lapathi is introduced to North America, it is not unreasonable to refer to these latter breaks as natural,) Natural breaks appeared to be associated with dead wood, but there was no significant correlation between the proportion of dead wood and the number of natural breaks at each site (r = 0.035, P = 0.68, n = 135). However, compared to live stems, dead stems were more likely to have been broken by natural causes (X2 =101.9, P <<0.0001, df = 1) and by C. lapethi attack plus natural causes (X2 -263.6, P <<0.0001, df = 1). Of the 510 C. lapathi-caused stem breaks retumed to the lab, 22.7% occuned at the junction of a btanch and the main stem. The mean diameter at a C. iapathkaused break was 21.6 mm (range 4 - 68 mm). As the diarneter of stems at the break point increased, the volume missing, as calculated by water displacement, increased exponentially (Figure 9). Srnall stems neeâed very little damage before becoming sufficiently weak to break; 43.9% of the 51 0 break points were >I5 mm diameter. The proportional amount of volume missing was weakly and negatively correlated with stem diameter at the break point (r = -0.249, n = 510, P < 0.0001). In some instances, breaks occurred after very little attack, e.g. at a dead patch of wood around an Figure 9. Relationstiip between the volume of stem misiing due to C. lapathi galleries as calculated by water displacement and the diameter of stems at the point of bnakage. Both volume and diameter log transformed prior to regression analysis. Break Diameter (mm) unsuccessful attack. If areas of moderate ta intense gallery density occur on opposite sides of the stem, a break could occur with a clean, slanted surface separating the attacked areas. Most breaks occurred across the stem with varying degrees of jaggedness, particularly for large diameter breaks. Naturally-occurring and C. IapathCinduced breaks had similar, but significantly different frequency distributions with respect to diameter and height (Figure 10). However, the peak for C. lapathi-caused breaks occurred in slightly larger diameter stems than those due to natural causes, and naturally-caused breaks almost always occurred higher on the stem than C. lapathi- caused breaks, probably because C. lapathi preferentially attacks near the base of stems (Saftanyik 1963). WITHIN-TREEDISTRIBUTION OF C. UPATHl Stems attacked by C. lapathi were proportionately longer and larger in basal diameter than would be expected if C. lapathi selected stems randomly (Figure 11). The relatively large number of stems 530 cm long is due to a significant number of C. lapathi-broken stems where the distal portion was no longer present. Large stems within trees (clumps) are also preferred, because attacked stems were significantly larger than attack-free stems for mean stem Iength (z = -8.43, P <0,0001, k = 69, n = 280), maximum stem Iength (z = -5.57, P <0.0001, k = 90, n = 273), mean stem basal diameter (z = -12.98, P <0.0001, k = 30, n = 277) and maximum stem basal diameter (z = 40.09, P <0.000?,k = 54, n = 277). As the levei of attack in a site increased, the ratio of attacked stems to 'large' stems ri7mm basal diameter also increased (Figure 12), indicating that as weevil pressure increased, small stems were chosen more frequently. Correlation analysis comparing the ratio of attacked to "largenstems, with respect to mean stem height (r = -0.00602, P = 0.95, n = 135). Iength (r = 0.M7, P = 0.63, n = 135), basal diameter (r = -0.0612, P = 0.48, n = 135) and basal area (r = 0.0694, P = 0.42, n = 135), ensured that there were no underiying differences in tree sue between sites with low and high pressure. Figure 10. Freqwncy distributions of C. Iapathb and naturally-caused breaks in relation to diameter of the stem at the break point and length of stem from the root collar to the break point. O Naturally-caused breaks C. lapethi-caused breaks DiAMETER OF STEM AT BREAK POINT x2 1102.1 5 P <0.0001 n = 1436 Diameter (upper limit of diameter class, mm) LENGTH OF STEM TO BREAK POINT x2 = 61.44 P = 0.0001 n = 1350 Length (upper limit of kngth clasr, cm) Figure 11. Frequency distributions of stem lengths and basal diameters, comparing al1 stems sampled to CDlapathif-attacked stems. O All Stems I Attacked Stems STEM LENGTHS x2 =285.46 P <0.0001 df = 34 nali= 4668 namm = 1537 O 60 120 180 240 300 360 420 480 540 600 66û 720 780 840 900 960 1020 Stem Length (upper limit of length class, cm) STEM BASAL DIAMETERS x2 =640.08 P <0*0001 df = 35 nail= 5058 namw = 1548 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 >1ôû Basal Diameter of Stem (upper limit of diameter class, mm) Figure 12. Relationship between the proportion of trees attacked by C. lapsthi in each site and the ratio of attacked to 'large' stems >If mm basal diameter. O 0.2 0.4 0.6 0.8 1 Proportion of Trees with Attack in Each Site The base of stems was preferentially attacked by C. lapathi (Figure 13). In repeatedly attacked trees, old attack occurred at a significantly lower minimum height and greater stem diameter than current-year attack (paired sign test, n = 285, k = 85, z = -6.75, P <0.0001; n = 236, k = 69, z = -6.31, P <0.0001,respectively). The maximum attack heigMs and coiresponding minimum diameters of old and current attack were not significantly different between old and currentattack(n =303,k= 151,z=0.0, P=0.50;andn =263, k= 121, z=-1.23, P=0,11, respectively). Possibly, as the base of the stem accumuiated attack, it rnay have becorne progressively unsuitable for oviposition (Safranyik 1963). Conclusions My research leads to 14 pertinent condusions, as outlined below. The known range of C. lapathi in B.C. has increased substantialy since 1963 (J.W.E. Harris 1964). The range now extends further northward to at least 54O 40' N in the interior of the province, and has reached Bella Coola on the central coast. Cryptothynchus lapathi is widespread across biogeoclimatic zones and subzones, and is found in the CWHds, CWHms, CWHvm, ESSFwm, ESSFxc, ICHdw, ICHmk, ICHvk, IDFdk, IDFww, IDFxh, SBSdw, SBSmc, and SBSwk. It was not detected in the ESSFmc subzone which was sampled between Hazelton and Srnithers, B.C. The single most important factor lirniting weevil abundance appears to be climate. Cold biogeoclirnatic subzones had significantly fewer attacked trees than wansubzones. Regression models can be derived that use dimatic factors to predict the expected proportion of attacked trees with 280% accuracy. The most important factors involved in these predictions were: number of months with mean temperature >tO°C, mean annual temperature (OC), number of frost free days, elevation, rnean temperature of the wamest month (OC). and accumulated day degrws >5OC. Figure 13. Frequency distribution of C. lapsthi attack range along the Iength of Salix stems. O 90 180 270 360 450 540 630 720 810 900 990 1080 Length of Stem at Point of Attack (upper limit of length class, cm) On-site factors such as Iight and water availability or host density do not appear to affect the abundance of C. lapathi attacked trees, although assessment of these factors was not done systernatically . The proportion of attacked trees is directly related to number of weevils in a population, the intensity of their attack, and therefore the impact. There is no evidence of host preference for any species of Salix, although some trees apparently escape attack by growing in cold locations. New host records for C. lapathi found in this survey are: S. barclayi, S. brachycarpa, S. drurnmondiana, S. geyeriana, S. glauca, S. hookenana, S. melanopsis, S. prolixa, S. pseudomonticola, S. pyrifolia, and S. silchensis. Compared to attack-free trees, attacked trees have significantly larger mean basal diameters, rnean stem lengths, maximum stem heights, more stems, more large diameter stems, and larger total basal area. They also have more stems that grow on an angle and therefore are longer than stems in attack-free trees, but attacked trees are net significantly taller than attack-free trees. IO. Compared to attack-free trees, attacked trees proportionately have more dead wood, more dead stems, more adventitious branches per stem, more total breaks per stem, and more breaks not associated with C. lapathi attack. Thus they suffer more within-tree mortality than attack-free trees. 11, Attack occurs predorninately at the base of stems. 12. Breaks caused by C. lapathi attack tend to occur at slightly larger stem diameters, and correspondingly lower on the stem, than "naturally" caused breaks. 13. As the diameter of a broken stem caused by C. lapethi attack increases, so does the total volume of stem material rnissing due to C. lapathi galleries, thus it appears more damage must be done on a large diarneter stem before it will break. Also, as the diameter of the stem break increases, so does the length of the break in profile. 14. Cryptorhynchus lapathi proportionately attacked a population of stems slightly larger in diameter and longer than the total population of stems. As the weevil becornes more abundant, it will attack smaller diameter stems, In summary, C. lapathi is now well established throughout the south half of the province and may be nearing the limits of its potential geographic range. Although the weevil can be very abundant on numerous Salix spp., and its damage to individual trees very severe, there is no evidence that species or populations of willow are threatened with extinction. The changes in tree structure, health, and the potential for Salix trees never reaching maximum size could, however, have ecological ramifications by changing plant community structure, composition or function. For example, although heavily attacked stems may be essentially coppiced, they likely wouldn't increase moose browse because there is decreased vigor and health in such stems; the vigorous and abundant new flush from mechanical cutting would be of superior quantity, quality and longevity for moose than adventitious branches following weevil attack. The increase in tree structural and possibly chernical complexity after attack as a direct result of induced tree response, stress, disease, death or stem breaks potentially could provide more habitat substrates and actually increase the diversity of organisms that could utilize the willow. This in tum could affect th8 abundance and distribution of numerous other organisms, from insectivorous birds and parasitic wasps to pathogens and mycorrhizae. Appendix Reported here in Tables 7 to 12 are the predicted proportions of attacked trees, along with the 95% confidence and 95% prediction intervais, as calculated by the three regression models. They are arranged in both alphabetical order and order of decreasing predicted proportion. Blanks indicate that at least one of the required climate factors was rnissing from the original data set. Some climate data were available for Alaska, the Yukon and Northwest Tenitories, Alberta, Washington, Idaho, and Montana so they have also been included. Table 7. Predicted proportions and confidence and prediction intervals for Modell ("MO) in order of decreasing predicted proportion. Actual Predicted Lower end of Upper end of Lower end of Upper end of Biogm- proportion of proporüon of a 95% a 95% a 95% a 95% climatic attacked attacked confidence confidence prediction prediction Zone Subzone trees trees intewal intewal interval interval CWH dm CDF mm CWH xml BG xhl CWH xm2 PP xhl CWH ds IDF WW BG xh2 BG xh3 BG xwl CWH dsl CWH ds2 ICH mw2 ICH mw3 ICH XW IDF dk1 IDF dm1 IDF mw2 IDF tl 1DF WW IDF xhl ,ww PP dhl PP dh2 PP xtl2 Idaho ICH dw ICH dw Montana IDF xhl IDÇ xh CWH vm CWH vml Washington IDF dm2 BG xw2 IDF xh2 SBS mh CWH vh 1 IDF mw1 CWH ms CWH ms1 CWH wsl CWH vh2 CWH whl ICH mk1 ICH vkl ICH wkl IDF xm IDF XW MH mmp2 SBS dh IDF dk ICH wk3 Alaska ICH mk SBS dw2 ICH mc2 ICH v k CWH wm IDF dk2 SES dwl SES dw IDF dk3 ESSF dk MS dk ICH mk3 ICH wk2 BWBS mwl IDF dk4 SES vk ses dw3 SBS wkl S8S wk ESSF wm BWBS dk2 BWBS mw2 8WBS wk2 ESSF mm1 ESSF mw fSSF wm ICH mm ICH VC ICH v k2 IDF au MH mm1 MS dm1 MS dm2 MS x k SBPS dc ses mk2 SBS rnw ses wk3 SBS wk3lmc sas dk SBS wk2 SBS mk1 SBPS mk SBS mc2 SBS rnc BWBS dk1 SBS mc3 BWBS wkl SEPS XC SWB mk ESSF XC ESSF rnk ESSF VC ESSF VCP ESSF XC SBPS mc ESSF wk2 ESSF mv2 ESSF mm MH mmpl ESSF mc ESSF mc ESSF wkl ESSF mv3 AT 9 AT b ESSF wc3 AT a BWBS mxl BWBS wk3 CWH vm2 ESSF wc3p ICH mwl MS xv Yukon N.W. Tenitories Alberta Table 8. Predicted proportions and confidence and pndictlon intervals for Mode11 ('MO) in alphabetical order. Actual Predicted Lower end Upper end Lower end Upper end proportion proportion of a 95% of a 95% of a 95% of a 95% Biogeo-climatic of attacked of attacked confidence confidence prediction prediction zone subzone trees trees interval interval intewal interval AT a b 4 BG xhl xh2 xh3 xwl xw2 BWBS dkl dk2 rnwl mw2 mx1 wkl wk2 wk3 CDF mm CWH dm ds dsl ds2 ms msl vhl vh2 vm vml vm2 whl wm wsl xm1 xm2 ESSF dk mc mk mm mm1 mv2 mv3 rnw VC VCP wc3 wc3p wkl wu wm XC ICH dw mc2 mk mkl mk3 mm mwl mw2 rnw3 VC vk v kl v k2 wkl wk2 wk3 xw IDF au dk dkl d k2 d k3 d k4 dm1 dm2 rnwl mw2 U WW xh xhl xhf ,ww xh2 xrn XW mm1 mmpl mmp2 dk dm1 dm2 xk xv dhl dh2 xh1 xh2 SBPS dc mc mk XC SBS dh dk dw dwt dw2 dw3 mc mc2 mc3 mh mkl m k2 niw vk wk wk1 wk2 wk3 wk3lmc SWB mk Yukon N.W. Tenitories Alberta Washington Idaho Montana Table 9. Predicted proportions and confidence and prediction Intervals for Modal 2 (MATl NFFD, €LE) in order of decreasing predicted proportion. Actual Predicted Lower end of Upper end of Lower end of Upper end of Biogeo- proportion of proportion of a 95% a 95% a 95% a 95% climatic attacked attacked confidence confidence piediction prediction zone Subzone trees irees interval intervat intewal interval BG xh 1 1.279 0.779 1.424 BG xh2 PP xh 1 IDF xhl ,ww PP xh2 ICH XW IDÇ mwl IDF dm1 IDF xh 1 IDF WW PP dhl IDF U IDF mw2 IDF x h IDF xh2 ICH dw IC H dw IDF WW BG xh3 CWH xml CWH ds 1 BG xwl IDF dkl ICH mw3 ICH mw2 PP dh2 CWH xm2 BG w2 CWH ds CWH dm CWH ms CWH rnsl CDF mm CWH ds2 IDF au SBS mh IDF dm2 SBS dwl IDF xm IDF dk IDF dk4 CWH vm1 CWH wsl ICH vk2 IDF dk2 CWH whl SBPS XC ESSF mw ICH wkl MS dm1 ICH vk ICH mk3 CH vkl ICH mk SBPS mk ICH mkl ICH wk2 ICH mc2 CWH wm CWH vm IDF d k3 SBS dw SBS dw3 CWH vh 1 MS x k MH mmp2 ESSF mk SBS wk1 SBS dh MS dk SBS dk ESSF wm ESSF wm SES dw2 CWH vh2 MH mm1 ESSF mm1 SBPS dc SBS wk SES rnkl MS dm2 ses mc2 ses mk2 BWBS mw1 ESSF VC Alberta BWBS mxl SES wk2 BWBS dkl ses mc ESSF XC ESSF XC ESSF dk ESSF wkl SWB mk BWBS mw2 ESSF VCP BWBS w k2 MH mmpl BWBS dk2 AT 9 Yukon ESSF wc3 ESSF mc AT a AT b BWBS wk1 swss wk3 CWH vm2 ESSF rnc ESSF mm ESSF rnv2 ESSF mv3 ESSF wc3p ESSF w k2 ICH mm ICH mwl ICH VC ICH w k3 IDF XW MS xv SBPS mc SES mc3 SBS mw S8S vk SBS wk3 SBS w k3trnc N.W. Territories Washington Idaho Montana Alaska Table 10. Predicted proportions and confidence and preâiction intervals for Mode12 (MAT, NFFD, €LE) in alphabetical order. Actual Predicted Lower end of Upper end of Lower end of Upper end of Biogeo- proportion of proportion of a 95% a 95% a 95% a 95% climaüc attacked attacked confidence confidence ~redicüon ~rediction zone Subzone trees trees intervat interval interval interval AT a b 9 BG xhl xh2 xh3 xwl xw2 BWBS dkl d k2 mwl mw2 mxl w kl w k2 wk3 CDF mm CWH dm ds dsl ds2 rns ms 1 vhl vh2 vm vml vm2 whl wm ws 1 xml xm2 ESSF dk mc mk mm mm1 mv2 mv3 mw mwl mcv2 mw3 VC vk vkl v k2 wkl wk2 w k3 xw IDF au dk dkl dk2 dk3 dk4 dm1 dm2 rnwl mw2 U WW WW xh xhl xtlt ,ww xh2 xm XW MH mm1 rnmp1 mmp2 MS dk dm1 dm2 xk XV PP dh1 dh2 xhl xh2 SBPS dc rnc rnk XC SBS dh dk dw dwl dw2 dw3 mc mc2 rnc3 mh rnkl mk2 mw vk wk wkl wk2 wk3 wk3lrnc SWB mk Yukon N.W. Territories Alberta Washington Idaho Montana Alaska Table 11. Predicted proportions and confidence and prodiction intewals for Mode13 (T>lO, MWM, DD>S) in order of decreasing predktrd proportion. Actual Predicted Lower end of Upper end of Lower end of Upper end of Biogeo- proportion of proportion of a 95% a 95% a 95% a 95% climatic attacked attacked confidence confidence prediction prediction zone Subzone trees trees intenral interval interval interval xw2 ICH mw3 PP dh2 PP xh2 IDF dm1 IDF mw2 IDF dm2 BG xhl ICH mw2 IDF U PP dhl PP xhl ICH dw ICH dw ICH xw BG xh3 SBS mh IDF dkl BG xw1 IDF xh2 [OF xh IDF xhl 1Df rnwl BG xh2 IDF WW IDF WW CWH ds 1 IDF xh1 ,ww ICH vkl CWH ds CWH xm2 CWH ms CWH msl CWH ds2 ICH wkl CWH dm MH mmp2 CWH xml IDF xm ICH mk1 SBS dh CDF mm CWH ws1 CWH vm CWH vml IDF dk CH vk MS dk ICH rnk IDF d k2 BWBS d k2 CWH wm ESSF dk MS xk ESSF wm ESSF wm BWBS mw1 IDF d k3 SBS dw2 SBS dwl SBS dw MS dm2 ICH wk2 ESSF mm1 CWH wh1 SBS dw3 ESSF mw ICH mk3 MS dm1 BWBS wk2 IDF au CWH vhl SBS wk2 IDF dk4 SBPS dc MH mm1 ICH vk2 CWH vh2 SBS wkl SBS dk ICH mc2 S8S mkl BWBS mw2 sas mk2 SBS wk ESSF VC SWB rnk SBS mc3 ESSF XC BWBS dk1 ESSF XC SOS rnc SBPS mk ESSF VCP ESSF mk SBS mc2 SBPS XC AT 9 MH mmpl ESSF wk1 ESSF wc3 ESSF Alas ka Al berta AT a AT b BWBS mxl BWBS wk2 BWBS wk3 CWH vm2 ESSF mc ESSF mm ESSF mv2 ESSF mv3 ESSF wc3p ESSF wk2 ICH mm ICH mwl ICH VC ICH wk3 Idaho !OF Montana MS xv N.W. Territories SBPS mc SBS mw S8S vk SBS wk3 SBS wk3Jmc Washington Yukon Table 12. Predicted proportions and confidence and prediction intervals for Mode13 (TMO, MTWM, DD>5) in afphabetical order. Actual Predicted Lower end of Upper end of Lower end of Upper end of Biogeo- proportion of proportion of a 95% a 95% a 95% a 95% clirnatic attacked attacked confidence confidence prediction predicüon zone Subzone trees trees intewal interval interval interval AT a b 9 BG xhl xh2 xh3 xwl xw2 BWBS dk1 dk2 mw1 mw2 mxl wk1 wk2 wk3 CDF mm CWH dm ds dsl ds2 ms msi vhl vh2 vm vml vm2 wh1 wm ws1 xml xm2 ESSF dk rnc rnk mm mm1 mv2 mv3 mw VC VCP wc3 W~P wkl wu wm XC ICH dw mc2 mk mkl mk3 mm mwl mw2 mw3 vc vk vkl vk2 wkl wk2 wk3 xw IDF au dk d kl d k2 d k3 dk4 dm1 dm2 mwl mw2 U WW WW xh xh1 xhl ,ww xh2 xm XW MH mm1 mmpl mmp2 MS dk dm1 dm2 xk XV PP dht dh2 xhl xh2 SBPS dc rnc rnk XC SBS dh dk dw dwl dw2 dw3 rnc rnc2 mc3 mh mkl mk2 rnw vk wk wkl wk2 wk3 wk3imc SWB mk Yukon N.W. 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