Examining the Potential of Western Larch, Siberian Larch, and Ponderosa Pine As Regeneration Species in Cariboo Region Ecosystems: 22-Year Results from EP904.02

T E C H N I C A L R E P O R T 0 9 6

Examining the Potential of Western Larch, Siberian Larch, and Ponderosa Pine as Regeneration Species in Cariboo Region Ecosystems: 22-year Results from EP904.02

2016

096 Examining the Potential of Western Larch, Siberian Larch, and Ponderosa Pine as Regeneration Species in Cariboo Region Ecosystems: 22-year Results from EP904.02

T.A. Newsome, J.L. Heineman, and A.F.L. Nemec The use of trade, ﬁrm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an ofﬁcial endorsement or approval by the Government of British Columbia of any product or service to the exclusion of any others that may also be suitable. Contents of this report are presented for discussion purposes only. Funding assistance does not imply endorsement of any statements or information contained herein by the Government of British Columbia. Uniform Resource Locators (urls), addresses, and contact information contained in this document are current at the time of printing unless otherwise noted.

ISBN 978-0-7726-6965-0 – Print version ISBN 978-0-7726-6966-7 – Digital version

Citation Newsome, T.A., J.L. Heineman, and A.F.L. Nemec. 2016. Examining the potential of western larch, Siberian larch, and ponderosa pine as regeneration species in Cariboo Region ecosystems: 22-year results from EP904.02. Prov. B.C., Victoria, B.C. Tech. Rep. 096. www.for.gov.bc.ca/hfd/pubs/Docs/ Tr/Tr096.htm

Prepared by Teresa A. Newsome B.C. Ministry of Forests, Lands and Natural Resource Operations Cariboo Region Williams Lake, B.C.

Jean L. Heineman J. Heineman Forestry Consulting Vancouver, B.C.

Amanda F. Linnell Nemec International Statistics and Research Corp. Brentwood Bay, B.C.

Copies of this report may be obtained, depending upon supply, from: Crown Publications, Queen’s Printer 2nd Floor, 563 Superior Street Victoria, BC v8w 9v7 1-800-663-6105 www.crownpub.bc.ca For more information on other publications in this series, visit www.for.gov.bc.ca/scripts/hfd/pubs/ hfdcatalog/index.asp © 2016 Province of British Columbia When using information from this report, please cite fully and correctly. Abstract

Experimental Project 904.02 (EP904.02) was established in 1987 to examine the performance of western larch (Larix occidentalis), Siberian larch (Larix sibirica), and ponderosa pine (Pinus ponderosa) at ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites in the Cariboo Region. Survival and growth of these non-native species over a 22-year period were compared with that of lodgepole pine (Pinus contorta var. latifolia), Douglas-fr (Pseudotsuga menziesii), and hybrid spruce (Picea engelmannii × glauca), which are common forest components in this region. Subsequent to the installation of this experiment, climate change–related forest health issues became an important management concern, and the exten- sion of species beyond their natural range was considered as a mitigation strategy. Western larch was a good candidate for assisted migration, and interim guidelines are now in place that allow this species to be planted in many Cariboo Region ecosystems. As a result of these recent changes, our 22-year western larch results are especially relevant to current forest management. Lodgepole pine, Douglas-fr, and hybrid spruce survived and grew according to general expectations for the individual biogeoclimatic units, except that lodgepole pine sustained high (40%) frst-year mortality at the ESSFwk1 site. At all locations, lodgepole pine grew more rapidly in early years than Douglas- fr or hybrid spruce, and continued to be larger at age 22. Douglas-fr, once established, survived and grew well at the ICHwk2 and SBSmw sites but did poorly at the SBPSxc installation. Hybrid spruce exhibited better overall survival than any other species but grew considerably more slowly than lodgepole pine or Douglas-fr throughout the 22-year assessment period. Western larch had higher survival and better growth at the ESSFwk1 than the ICHwk2 or SBSmw sites, possibly because the seedlot used at the ESSF- wk1 installation was better adapted to moist conditions than that used elsewhere. After 22 years, 79% of western larch survived at the ESSFwk1 site, and trees were approximately as tall as lodgepole pine. Within its current range, western larch is not common in the ESSF zone, and we speculate that if a more suitable seedlot had been used at our ICHwk2 and SBSmw sites, western larch growth would have at least equalled that at the ESSFwk1 location. Western larch had very low survival and was unable to increase in height at the SBPSxc site, apparently because it was as ill-suited as Douglas- fr to the harsh climatic conditions of the Chilcotin plateau. Siberian larch survival was equal to or better than that of western larch at all the experimental locations, but after 22 years, it was approximately 1 m shorter than western larch at the ESSFwk1 and SBSmw sites. Both larches sustained considerable forking damage, but from a growth and yield perspective, Siberian larch had the more serious defects. At the SBPSxc site, severe forking notwithstanding, Siberian larch had the second-best survival after lodgepole pine and was the only other species that was even marginally able to withstand the climatic limitations of that location. Ponderosa pine survived and grew reasonably well at the SBSmw and ICHwk2 sites, but tended to increase in diameter at the expense of height and was subjectively observed to have large branches and wide crowns, traits that do not suggest high economic value. Like all other species except lodgepole pine, ponderosa pine did poorly at the SBPSxc site.

iii ACKNOWLEDGEMENTS

The authors would like to thank Craig Sutherland for co-ordinating and over- seeing the project, and West Fraser Mills Ltd. for acquiring the Siberian larch seed and providing ongoing technical and fnancial support. We are grateful to Gerry Chapman, George White, and Doug Routledge for selecting sites and establishing individual experiments. We thank Kirsteen Laing and Larry McCulloch for initial assessments and data summaries, and Eva Fickell, Janet and Scott Zimonick, and Industrial Forestry Services employees for later data collection. We also thank Barry Jaquish, Deb MacKillop, Peter Ott, and Allan Powelson for providing helpful review comments. Funding assistance was re- ceived from the B.C. Ministry of Forests, the Forest Investment Account, and West Fraser Mills Ltd. Funding assistance does not imply endorsement of any statement or information in this report.

iv Contents

Abstract...... iii Acknowledgements...... iv 1 Introduction ...... 1 2 Methods...... 4 2.1 Study Areas...... 4 2.2 Experimental Design and Treatments...... 4 2.3 Measurements ...... 5 2.4 Data Calculations and Statistical Analysis...... 5 3 Results...... 6 3.1 Survival, Vigour, and Overtopping...... 6 3.1.1 Western larch...... 6 3.1.2 Siberian larch...... 7 3.1.3 Lodgepole pine ...... 7 3.1.4 Douglas-fr...... 11 3.1.5 Hybrid spruce...... 11 3.1.6 Ponderosa pine...... 11 3.2 Damage and Damaging Agents in Years 1−16...... 12 3.2.1 Hare and frost damage...... 12 3.2.2 Leader damage and forking ...... 12 3.2.3 Species-specifc damaging agents...... 13 3.3 Growth...... 16 3.3.1 Between-site comparison of size and growth rates for individual species...... 17 3.3.2 Between-species size and growth rate comparison at the ICHwk2, SBSmw, and ESSFwk1 sites ...... 23 3.4 Stand-level Responses...... 26 3.4.1 Year 22 tree condition according to growth and yield damage criteria...... 26 3.4.2 Gross stand volume per hectare...... 27 3.4.3 Site index...... 28 4 Discussion...... 29 4.1 Lodgepole Pine, Douglas-fr, and Hybrid Spruce...... 30 4.2 Western Larch...... 31 4.3 Siberian Larch ...... 33 4.4 Ponderosa Pine ...... 33 4.5 Management Considerations...... 34 5 Conclusion...... 36 Literature Cited ...... 37

APpendices 1 Stocktype, seedlot, and nursery information...... 41 2 Assessment codes for vigour, overtopping, damage, and damage cause. . 42

v tables 1 ep904.02 site and climatic characteristics...... 3 2 Overlap of western larch seed planning zones lw1 and lw2 with Cariboo Region ICHwk, SBSmw, ESSFwk, and SBPSxc subzones...... 4 3 Site–species combinations examined in ep904.02...... 4 4 p-values indicating statistical signifcance of interactions between site and species for size and growth variables between year 3 and year 22. . . . 16 5 Site effects on mean height of individual tree species in year 3, year 5, year 10, year 16, and year 22...... 17 6 Site effects on mean height and diameter growth of individual species for year 10−16, 16−22, and 21−22 intervals...... 18 7 Site effects on mean ground-level diameter in year 3, year 5, year 10, and year 16, and mean diameter at 1.3 m in year 22...... 19 8 Site effects on mean stem volume for individual tree species in years 16 and 22, and volume growth from years 16–22...... 20 9 Proportion of live trees affected by specifc damage types and damaging agents in the year 22 growth and yield assessment at the ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites...... 27 10 Mean year 22 site index estimated from year 22 tree size for individual tree species at the ICHwk2, SBSmw1, ESSFwk1, and SBPSxc sites...... 29

Figures 1 ep904.02 study site locations...... 2 2 Survival from planting to year 22 for western larch, Siberian larch, lodgepole pine, Douglas-fr, hybrid spruce, and ponderosa pine at individual sites...... 8 3 Vigour and overtopping of western larch, Siberian larch, lodgepole pine, Douglas-fr, hybrid spruce, and ponderosa pine in years 3, 5, 16, and 22 at individual sites ...... 10 4 Proportion of live trees of all species affected by hare damage in years 1 and 3 at the ICHwk2 site only, and live Siberian larch and Douglas-fr affected by frost damage in year 1 at the SBSmw and SBPSxc sites . . . 13 5 Survival and proportion of live western larch, Siberian larch, lodgepole pine, Douglas-fr, hybrid spruce, and ponderosa pine with leader or stem damage in years 1, 3, 5, 10, and 16 at individual sites. . . 14 6 Year 16 proportion of live lodgepole pine and ponderosa pine with western gall rust stem or branch infections, lodgepole pine and ponderosa pine with pine needle cast, and hybrid spruce with cooley gall adelgid branch galls at individual sites...... 15 7 Comparison of year 22 height, year 10–16 height growth, year 16–22 height growth, and year 21–22 height growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites...... 24 8 Comparison of year 22 dbh and year 16–22 dbh growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites...... 25 9 Comparison of year 22 stem volume and year 16–22 stem volume growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites. 26 10 Comparison of year 22 gross stand volume per hectare for individual species at the ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites...... 28 11 Comparison of year 22 gross stand volume per hectare at ICHwk2, SBSmw, and ESSFwk1 sites for western larch, Siberian larch, lodgepole pine, Douglas-fr, hybrid spruce, and ponderosa pine...... 29

vi 1 INTRODUCTION

Guidelines for selecting conifer species to regenerate harvested sites in British Columbia take into consideration natural distributions, ecological suitability, and factors related to forest health and productivity (B.C. Ministry of Forests 2002). In the past, the performance of indigenous species outside their natural ranges, and of non-native species, was largely speculative in British Columbia because our requirements were satisfed by the wide diversity of native species and the general good health of our forests. In response to the recent mountain pine beetle epidemic (B.C. Ministry of Forests and Range 2007) and projected climate-change effects on forest health and species distribution (Spittlehouse 2008; Kliejunas et al. 2009), there is now greater practical interest in expand- ing the range of acceptable species. One of the primary candidates for facilitated migration is western larch (Larix occidentalis), which is the most productive interior conifer species in British Columbia. This shade-intolerant species is best suited to medium to rich, moderately to slightly dry sites, and under optimum conditions, it can attain site indices of up to 30 m (B.C. Ministry of Forests, Lands and Natural Resource Operations 2013). It has the beneft of having relatively few serious health problems (Henigman et al. 2001), and it produces high-quality wood that is suitable for a range of products (Keegan et al. 1995; Parent et al. 2008). At present, western larch’s natural distribution in British Columbia is restricted to the southeastern portion of the province, but a recent in-depth modelling project by Rehfeldt and Jaquish (2010) suggested that its potential niche, especially as climate change is realized, extends considerably further north. On the basis of this work, seed planning zones (LW1 and LW2) were defned for western larch in central interior British Columbia, and interim guidelines were implemented to allow the inclusion of up to 10% western larch in management units within these zones (B.C. Ministry of Forests and Range 20101; B.C. Min- istry of Forests, Lands and Natural Resource Operations 2014). Siberian larch (Larix sibirica), which is native to northeastern parts of Euro- pean Russia and western Siberia, is also of academic interest because it has high productivity in regions that are climatically similar to parts of north and central British Columbia. In particular, the Raivola provenance, which originated from a stand established in 1738 near St. Petersburg to provide the Russian navy with raw material for shipbuilding, has caught the interest of researchers, since it is capable of attaining stand volumes of up to 1000 m3/ha (Viherä-Aarnio and Nikkanen 1995). Smith (1986) stated that the most important factor for successful introduction of exotic tree species is the similarity of climate and soils to the native region. He points out that dramatic movements of species across major geographic barriers to similar habitats may be more successful than seemingly modest extensions of natural ranges. Possibly because we have such a wealth of indigenous species, the introduction of exotic species has never been seriously contemplated in British Columbia. However, the process has been successful in other parts of the world—the most well-known being the successful introduction of Douglas-fr (Pseudotsuga menziesii) to the United Kingdom and Europe, and Monterey pine (Pinus radiata) to areas in the southern hemisphere that are

1 British Columbia Ministry of Forests and Range. 2010. Interim measures for the assisted range and population expansion of western larch for use as a climate change adaptation strategy in British Columbia. Tree Improvement Br., Victoria, B.C. Unpubl. rep.

1 environmentally similar to California. Siberian larch is currently used to some extent in Scandinavian forest management; however, research to identify suitable provenances and seed sources for that region is ongoing (Martinsson 1995; Larsson-Stern 2003). Although long-term feld experiments that monitor species−site relation- ships are somewhat limited by the small number of seedlots they involve (and hence they involve little genetic variation) and by variation that can be introduced when stock is sourced from more than one nursery, they are nonetheless a good source of information for considering the assisted move- ment or introduction of tree species (Aitken et al. 2008). In 1988, a species study (Experimental Project 904.02 [EP904.02]) was undertaken in the Cari- boo Region of south−central British Columbia to compare the performance of western and Siberian larch with that of lodgepole pine (Pinus contorta var. latifolia), Douglas-fr, and hybrid spruce (Picea engelmannii × glauca), which occur naturally in that geographic area. Out of interest about its ability to perform north of its natural range, ponderosa pine (Pinus ponderosa) was also included in the experiment. Experimental Project 904.02 was designed to encompass the wide diversity of ecosystems that occur in the Cariboo Region (Steen and Coupé 1997). It included single replicates on zonal sites in four biogeoclimatic subzones or variants (Figure 1). Limitations to conifer seedling establishment were anticipated to be most severe at the SBPSxc site, which had a high frost hazard rating (Steen et al. 1990). Limitations were also expected to be somewhat greater at

^ Study site ! Biogeoclimatic zone ^ESSFwk1 site Bunchgrass

Engelmann Spruce–Subalpine Fir Wells ! Interior Cedar Hemlock Interior Douglas-Fir ^ SBSmw site Montane Spruce Quesnel Sub-Boreal Pine-Spruce (! Kersley Sub-Boreal Spruce

(! ^ ICHwk2 site McLeese Lake Horsefly (!

150 Mile House Williams Lake (! Alexis Creek (!

^ SBPSxc site

Kilometres 0 10 20 40 60 80

 1 ep904.02 study site locations.

2 the ESSFwk1 site than at the ICHwk2 or SBSmw sites, mainly because of the higher elevation of the ESSFwk1 installation, and because that biogeoclimatic variant is subject to heavy snowloads (Steen and Coupé 1997). Climatic characteristics of the research sites are provided in Table 1. Experimental Project 904.02 was established long before the interim guidelines for larch use came into being (B.C. Ministry of Forests, Lands and Natural Resource Operations 2014). Although none of our sites are precisely within the LW1 or LW2 seed planning zones (Table 2), the 22-year western larch responses are of interest because all the biogeoclimatic subzones we examined have some degree of overlap with the seed planning zones.

TABLE 1 ep904.02 site and climatic characteristics

Site ICHwk2 SBSmw ESSFwk1 SBPSxc Site characteristics Opening number 93A 036-71 93B 099(TFL 52) 93H 031(TFL 52) 93B 006-253 Latitude/longitude N52°22.81', N52°57.68', N53°18.21', N52°00.42', W120°57.35' W122°14.65' W121°50.54' W122°50.79' Site series 01 01 01 01 Elevation 1140 m 850 m 1340 m 1250 m Relative soil moisture regimea Mesic to subhygric Mesic Mesic Mesic Actual soil moistue regimea Fresh to moist Fresh Moist Moderately dry Slope position Mid–lower slope Flat Mid slope Flat Topography N/A Undulating N/A Flat Slope (%) 15–40% N/A 15–25% N/A Aspect NW N/A SW N/A Site history Clearcut 1985 Clearcut 1985 Clearcut 1985/86 Clearcut 1983 Broadcast burn 1986 Broadcast burn 1986 Broadcast burn 1986 Disc trenched 1986 Previous timber type CwFd 841 Unknown Unknown Pl 210 Recommended regeneration speciesb 1°: Fd, Pl, Sx 1°: Fd, Pl, Sx 1°: Se, Bl 1°: Pl 2°: Bl, Cw, Hw 2°: Bl 2°: Pl 2°: none Climatec Mean annual temperature (° C) 3.4 4.2 2.1 2.7 Mean warmest month temperature (° C) 14.1 15.5 12.1 13.7 Mean coldest month temperature (° C) –7.2 –7.0 –7.1 –8.5 Number of frost-free days 155 165 147 132 Continuous frost-free period (days) 98 107 96 75 Mean annual precipitation (mm) 847 603 978 502 Mean summer precipitation (mm) 399 291 393 229 Precipitation as snow (mm) 294 191 450 193 a Relative soil moisture regime is moisture regime relative to moisture availability, while actual soil moisture regime refers to moisture availability without regard to ecosystem (values from Steen and Coupé 1997). b Fd is Douglas-fr; Pl is lodgepole pine; Sx is hybrid spruce; Bl is subalpine fr; Cw is western redcedar; Hw is western hemlock. c From Climate BC, using normals 1971−2000 (updated July 5, 2015).

3 TABLE 2 Overlap of western larch seed planning zones lw1 and lw2 with Cariboo Region ICHwk, SBSmw, ESSFwk, and SBPSxc subzonesa

Total area in Area overlap- Proportion of sub- Cariboo Region ping lw1 or zone designated as Subzone (ha) lw2 (ha) lw1 or lw2 Location of research site relative to lw1 and lw2 ICHwk 303 207 167 529 55% Less than 1 km east of lw2 (northeast of Williams Lake) SBSmw 137 549 104 489 76% Approximately 2.5 km west and 1 km east, respectively, of narrow lw2 and lw1 areas that occur to the east of Quesnel ESSFwk 319 744 37 032 12% 25–30 km east of lw2 (northeast of Quesnel) SBPSxc 1 135 350 49 756 4% A minimum of 30 km from substantive lw1 boundaries that surround the Chilcotin plateau a Based on information provided by Geospatial Services, B.C. Ministry of Forests, Lands and Natural Resource Operations (Jan. 2016).

2 METHODS

2 .1 Study Areas The experiment includes a single site in each of four biogeoclimatic subzones or subzone variants: (1) Quesnel variant of the wet, cool Interior Cedar – Hem- lock zone (ICHwk2), (2) moist warm Sub-Boreal Spruce zone (SBSmw), (3) Cariboo variant of the wet, cool Engelmann Spruce – Subalpine Fir zone (ESS- Fwk1), and (4) very dry, cold Sub-Boreal − Pine Spruce zone (SBPSxc). The SBPSxc site had been classifed as IDFdk4 at the start of the study (Newsome et al. 1995) but was later reclassifed when biogeoclimatic boundaries were re- drawn. Individual site and climate characteristics are provided in Table 1.

2 .2 Experimental The experiment consisted of four separate randomized block designs, one at Design and each of the four biogeoclimatic subzones/variants (sites). At each site, plantings Treatments of up to six tree species were replicated in three blocks (western larch [Lw], Si- berian larch [Ls], hybrid spruce [Sx], Douglas-fr [Fd], lodgepole pine [Pl], and ponderosa pine [Py]). Site × species combinations are shown in Table 3.

TABLE 3 Site (subzone/variant)–species combinations examined in ep904.02

Site (subzone/variant) Species ICHwk2 SBSmw ESSFwk1 SBPS×c Western larch × × × × Siberian larch × × × × Lodgepole pine × × × × Douglas-fr × × × Hybrid spruce × × × Ponderosa pine × × ×

Douglas-fr and ponderosa pine were excluded from the ESSFwk1 site, which was clearly above the elevational range of those species, and hybrid spruce was excluded from the SBPSxc site due to the dryness of that ecosystem (the site was originally thought to be IDFdk4). At each site, each species (six at the ICHwk2 and SBSmw sites, four at the ESSFwk1 site, and fve at the SBPSxc site) was randomly assigned to a single plot measuring 25 × 25 m within each of three blocks. Blocks measured 50 × 75 m at the ICHwk2, SBSmw,

4 and SBPSxc sites, where fve or six species were examined, and 25 × 100 m at the ESSFwk1 site, where only four species were examined. Seedlings were planted on a 12 × 12 grid within each plot, at 2-m spacing, for a total of 144 trees per plot. In each plot, the 44 perimeter trees were left as a buffer, and the inner 100 trees, which were arranged on a 10 × 10 grid that was approximately 20 × 20 m (400 m2), were intended for eventual growth and yield assessment. Of these inner 100 trees, the frst 50 (i.e., trees in the frst fve rows) were tagged at the time of planting for regular assessment. In total, 150 trees of each species at each site and 3150 trees in the experiment as a whole were assessed at regular intervals. In year 22, the remaining 50 inner trees in each plot were tagged to allow growth and yield assessment of all 100 inner trees in each plot. Stocktype, seedlot, and nursery information is provided in Appendix 1. Seed- lings were planted in spring 1987, with the exception of western larch at the ESSFwk1 site, which was planted in spring 1988 due to an insufficiency of stock in 1987. As a result, western larch planted at the ESSFwk1 site was grown from a different seedlot than stock used at the other sites.

2 .3 Measurements With the exception of western larch at the ESSFwk1 site, the frst 50 measurement trees in each plot were assessed after growth was complete in years 1 (1987), 2 (1988), 3 (1989), 5 (1991), 10 (1996), 16 (2002), and 22 (2008). Assess- ments for western larch at the ESSFwk1 site were delayed by 1 year to compensate for the 1-year planting delay. Hereafter, for simplicity of present- ing results, western larch results will be presented as if they followed the same measurement schedule as the other species. During each assessment, height (± 5 cm) and diameter (± 0.1 cm) were measured. Diameter was measured at ground level (GLD) up to year 16, and at breast height (1.3 m) (dbh) in years 16 and 22. Survival, vigour, type and cause of damage, and degree of overtopping of measurement trees by competing vegetation were assessed in years 1, 2, 3, 5, 10, and 16 according to Cariboo Region Research Section codes that were current for the assessment year (Appendix 2). In year 22, survival of the frst 50 measurement trees in each plot was assessed, but vigour, type and cause of damage, and overtopping were not assessed as they had been in previous years. In the year 22 assessment, trees 51–100 (which had not been assessed previously) were measured for height and dbh, so that, together with data for trees 1–50, gross stand volume per hectare could be determined based on volume in the known plot area of 400 m2. In the year 22 assessment, damage agent and damage severity data were collected according to B.C. Ministry of Sustainable Resource Management (2003) criteria for all 100 measured trees. Specifc causes of tree mortality were not recorded in any years. In this report, for the frst 50 measurement trees, we present survival for years 1, 3, 5, 10, 16, and 22, overtopping for years 3, 5, 10, and 16, and vigour and growth for years 3, 5, 10, 16, and 22. For the full set of 100 measured trees, we present gross stand volume, damage agent, and damage severity results for year 22.

2 .4 Data Calculations All data were checked for outliers and normality prior to, and as part of, the and Statistical analysis. Individual tree volumes for years 16 and 22 were calculated using Analysis Kozak’s (1988) taper equations. Height growth was calculated for the intervals corresponding to 10−16, 16−22, and 21−22 years post planting. Diameter growth was calculated for the interval 10−16 years post planting based on GLD and for the interval 16−22 years post planting based on dbh. Volume growth was calculated for the interval 16−22 years. Categorical variables were

5 summarized as percent frequencies. Damage summaries included only trees with good, fair, or poor vigour; damage to moribund trees was excluded because it was inconsistently collected for trees that were very close to death. Site index was estimated by dividing the area occupied by the frst 50 measurement trees (which had been measured repeatedly since the start of the study) into approximately 0.01-ha subplots, selecting the largest dbh planted tree in each subplot as a site tree based on year 22 measurements, and apply- ing the following growth intercept models: western larch and Siberian larch (Nigh et al. 1999), lodgepole pine (Nigh 1997b), Douglas-fr (Nigh 1997a), hybrid spruce (Nigh 1999), and ponderosa pine (Nigh 2002). For the ICHwk2, SBSmw, and ESSFwk1, six trees of each species per site contributed to the site index calculations. In the SBPSxc, six trees contributed to site index determination for Siberian larch and lodgepole pine, and fve contributed to the value for ponderosa pine. Only two trees contributed to site index determination for western larch because so few achieved breast height. Similarly, site index could not be determined for Douglas-fr because trees did not achieve breast height. Mixed-effects analysis of variance ANOVA( ) was used to assess the interac- tive effects of site and species on the height, diameter, and volume of trees (excluding those in moribund condition). All analyses were based on a split- plot ANOVA model with (excluding the sub-sampling [tree] error) fxed site (i.e., subzone/variant)—the grouping factor for the main plots (i.e., blocks), species minus the split-plot factor, and site × species effects, and random block (nested in site) and block × species effects. We tested for an overall site × species interaction (degrees of freedom = 12 rather than the 15 that would have been used for a design where all 24 species–site combinations were represented) and constructed a series of contrasts to test for a site × species interaction at each pair of sites (degrees of freedom for each pair of sites = number of species common to the two sites minus 1). To simplify interpretation of the interactions, separate analyses were also performed by site and by species. The Bonferroni method of multiple comparisons was used to assess the signifcance of differences among relevant species or site means.2

3 RESULTS

3 .1 Survival, Vigour, 3.1.1 Western larch Year 22 survival of western larch at our four study sites and Overtopping decreased in the order of ESSFwk1 (79%) > ICHwk2 (50%) > SBSmw (43%) > SBPSxc (24%), a trend that was established as early as year 1 (Figure 2a). At the ESSFwk1 site, 5% of western larch died within 1 year of planting, and 13% had died by year 3, after which survival decreased very gradually over time. The proportion of the original measurement trees in good or fair vigour at the ESSFwk1 installation remained relatively constant (67–74%) from year 3 to year 22 (Figure 3a). At the ICHwk2, SBSmw, and SBPSxc sites, survival declined to 81%, 75%, and 75%, respectively, during the frst growing season, after which there were ongoing, relatively steady losses to age 22 (Figure 2a). At the ICHwk2 site, western larch vigour declined steeply between years 10 and 16, and there was a similar decline between years 5 and 10 at the SBSmw

2 All data analyses for this report were generated using SAS/STAT software, Version 9.3 of theSAS Sys- tem for Windows Copyright © 2002–2010 SAS Institute Inc. SAS and all other SAS Institute Inc. product or service names are registered trademarks or trademarks of SAS Institute Inc., Cary, NC, USA.

6 site (Figure 3a). There was some vigour recovery at both locations, resulting in about 40% of the original planted trees having good or fair vigour in year 22. At the SBPSxc site, almost all surviving western larch had poor vigour or were moribund from year 3 onwards (Figure 3a). At the ICHwk2 location, 33% and 38% of surviving western larch were overtopped in years 3 and 5, respectively, but almost none were overtopped in years 10 and 16 (Figure 3a). Approximately 20% of live western larch were overtopped in year 3 at the SBSmw site; the proportion of overtopped trees declined slightly by year 5, and in years 10 and 16, almost none were overtopped. Overtopping of western larch was minor at the ESSFwk1 (maximum 12% in year 5) and the SBPSxc (maximum 6% in year 16) sites.

3.1.2 Siberian larch Year 22 Siberian larch survival was higher than that of western larch at all four sites, and declined in the order of ESSFwk1 (81%) > ICHwk2 (73%) > SBSmw (66%) > SBPSxc (54%); again, this trend was established in year 1 (Figure 2b). There was no frst-year mortality of Siberian larch at the ESSFwk1 installation, but 16%, 24%, and 32% of seedlings at the ICHwk2, SBSmw, and SBPSxc sites, respectively, died within 1 year of planting. Declines in survival after year 1 were fairly gradual at all locations. At the SBSmw site, almost all Siberian larch that survived to year 3 consistently had good or fair vigour through year 22 (Figure 3b). In contrast, at the ESSFwk1 site where survival was highest, a small proportion of trees had poor vigour; this was also true at the ICHwk2 location, although by year 22, nearly all survivors at that site were in good or fair vigour. At age 22, the proportion of the original measurement trees that had good or fair vigour was the same (71%) at the ESSFwk1 and ICHwk2 sites, and was slightly lower (66%) at the SBSmw installation. At the SBPSxc site, approximately one-half to two-thirds of survivors had at least fair vigour through year 10, but most were in poor condition in years 16 and 22 (Figure 3b). Approximately 20% of surviving Siberian larch at the ICHwk2 site were overtopped in year 3, and this increased to nearly 40% by year 5 (Figure 3b). In years 10 and 16, presumably as trees outgrew surrounding vegetation, there was very little overtopping of Siberian larch at this location. Approximately 20% of surviving Siberian larch were overtopped in year 3 at the ESSFwk1 site. The proportion decreased slightly by year 5, and almost none of the ESSFwk1 Siberian larch were overtopped in years 10 or 16. Very few of the surviving Si- berian larch at the SBSmw or SBPSxc installations were overtopped in any of the assessment years.

3.1.3 Lodgepole pine Lodgepole pine survival at the ICHwk2 and SBPSxc sites was similarly high (≥ 89%) throughout the 22-year assessment period (Figure 2c), but vigour trends differed between these locations (Figure 3c). At the ICHwk2 site, approximately one-third of surviving pine had poor vigour in year 3, after which condition improved steadily until year 10. A small proportion of pine at this installation had poor vigour again in years 16 and 22; however, most (80%) were in good or fair condition. At the SBPSxc site, although more than 90% of pine survived to year 22, vigour declined after year 10; only 61% of the original measurement trees were in good or fair condition in years 16 and 22. At the SBSmw and ESSFwk1 sites, lodgepole pine survival declined to 85% and 60%, respectively, within 1 year of planting (Figure 2c).

7 ESSFwk1 ICHwk2 (a) Western larch SBSmw SBPSxc

100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year (b) Siberian larch

100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year (c) Lodgepole pine

100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year

 2 Survival from planting to year 22 for (a) western larch, (b) Siberian larch, (c) lodgepole pine, (d) Douglas-fir, (e) hybrid spruce, and (f) ponderosa pine at individual sites.

8 ESSFwk1 ICHwk2 (d) Douglas-fir SBSmw SBPSxc

100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year

(e) Hybrid spruce 100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year

(f) Ponderosa pine 100 90 80 70 60 50 40 Survival (%) 30 20 10 0 P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Year

 2 Continued

9 22 22 22 16 16 16 10 10 10 SBPSxc SBPSxc ESSFwk1 5 5 5 3 3 3 22 22 22 16 16 16 10 10 10 SBSmw SBSmw SBSmw 5 5 5 3 3 3 22 22 22 16 16 16 Overtoppedd 10 10 10 ICHwk2 ICHwk2 ICHwk2 5 5 5 3 3 3 0 0 0

80 60 40 20 80 60 40 20 80 60 40 20

100 100 100 Proportion of trees (%) trees of Proportion (%) trees of Proportion (%) trees of Proportion (d) Douglas-fir (e) Hybrid spruce Moribund (f) Ponderosa pine 22 22 22 Poor 16 16 16 10 10 10 SBPSxc SBPSxc SBPSxc 5 5 5 3 3 3 Fair 22 22 22 16 16 16 10 10 10 ESSFwk1 ESSFwk1 ESSFwk1 5 5 5 Good 3 3 3 22 22 22 16 16 16 10 10 10 SBSmw SBSmw SBSmw 5 5 5 3 3 3 22 22 22 16 16 16 10 10 10 ICHwk2 ICHwk2 ICHwk2 5 5 5 Vigour (proportion of original planted trees) and overtopping surviving trees that are overtopped) of (a) western larch, Vigour (e) hybrid spruce, and (f) ponderosa pine in years 3, 5, 16, 22 at individual (c) lodgepole pine, (d) Douglas-fir, (b) Siberian larch, sites. Overtopping data were not collected in year 22. 3 3 3

0 0 0

80 60 40 20 80 60 40 20 80 60 40 20

100 100 100 Proportion of trees (%) trees of Proportion (%) trees of Proportion (%) trees of Proportion (a) Western larch (a) Western (b) Siberian larch (c) Lodgepole pine 3  

10 After year 1, survival remained stable at the ESSFwk1 site, whereas at the SBSmw installation, it declined relatively steeply until year 5 and then stabi- lized. In year 22, lodgepole pine survival was similar (59−62%) at the two locations. At the ESSFwk1 and SBSmw sites, most pine that survived to year 3 had good or fair vigour through to year 22 (Figure 3c). At the ICHwk2 site, 34% and 30% of surviving lodgepole pine were overtopped in years 3 and 5, respectively, but nearly all were taller than the surrounding vegetation in years 10 and 16 (Figure 3c). At the ESSFwk1 installation, 25% of pine were overtopped in year 3, but almost none were overtopped in years 5, 10, or 16. There was minor pine overtopping at the SBSmw installation in years 3 and 5 (≤ 6%) and none in any assessment year at the SBPSxc site.

3.1.4 Douglas-fir Douglas-fr at the SBSmw, ICHwk2, and SBPSxc sites had similar year 1 survival (91−93%) (Figure 2d). After year 1, survival at the SBSmw and ICHwk2 locations gradually diverged until it was 73% and 58%, respectively, in year 22. At the SBSmw site, most surviving Douglas-fr were in good or fair vigour at all assessment dates (Figure 3d). In contrast, more than one-half of the surviving Douglas-fr at the ICHwk2 installation were in poor or moribund condition in year 3, after which vigour improved consistently until year 10. Although Douglas-fr survival declined between years 10 and 16 at the ICHwk2 site, nearly all live trees continued to have good or fair vigour. At the SBPSxc installation, survival declined steadily after planting to 18% in year 22 (Figure 2d). Nearly all surviving Douglas-fr at this site were in poor condition or moribund throughout the 22-year assessment period (Figure 3d). Approximately one-half (49%) of the surviving Douglas-fr at the ICHwk2 installation were overtopped in year 3, and the proportion increased to 66% by year 5 (Figure 3d). Most survivors grew through surrounding vegetation after year 5, so that ≤ 7% were overtopped in years 10 and 16. Overtopping of Douglas-fr was less severe at the SBSmw site, but again, it increased between years 3 and 5 (from 26 to 34%) before declining to less than 6% in years 10 and 16. At the SBPSxc location, none of the surviving Douglas-fr were overtopped in any assessment year.

3.1.5 Hybrid spruce Throughout the 22-year assessment period, hybrid spruce survival was ≥ 91% at the ICHwk2 and ESSFwk1 sites, and ≥ 84% at the SBSmw site (Figure 2e). With the exception of a short period of decline in condition in year 16 at the SBSmw location, most spruce consistently had good or fair vigour (Figure 3e). Twelve percent of live spruce at the ICHwk2 site were overtopped in year 3, and this increased to 30% by year 5 (Figure 3e). In years 10 and 16, overtopping of spruce at this location was minimal (2−3%). At the SBSmw site, 11% of surviving spruce were overtopped in year 3; the proportion increased to 26% in year 5, decreased to 3% in year 10, and then increased again to 15% in year 16. At the ESSFwk1 installation, 46% of surviving spruce were overtopped in year 3, but the proportion decreased to 15% by year 5 and was minimal in years 10 and 16 (≤ 4%).

3.1.6 Ponderosa pine Year 1 ponderosa pine survival was higher (94−99%) at the ICHwk2 and SBPSxc sites than at the SBSmw location (80%) (Figure 2f).

11 Between years 1 and 5, survival at the ICHwk2 site declined steeply to 59%, and then gradually to 53% in year 22. At the SBSmw site, ponderosa pine survival after year 1 declined gradually but steadily until it was 60% in year 22. Ponder- osa pine survival at the SBPSxc installation was high until year 10 (≥ 88%), after which it declined precipitously to 34% in year 16 and 21% in year 22. Pon- derosa pine vigour trends differed at the three locations (Figure 3f). Most surviving ponderosa pine at the ICHwk2 site had poor vigour in year 3, but condition improved markedly by year 10, likely because survivors were out- growing surrounding vegetation. Beyond age 10, nearly all survivors had good or fair vigour. At the SBSmw installation, almost all surviving ponderosa pine had good or fair vigour at all assessment dates, while at the SBPSxc site, vigour declined steadily through the 22-year assessment period (Figure 3f). At the ICHwk2 installation, 55% of surviving ponderosa pine were overtopped in year 3, and the proportion increased to 65% by year 5 (Figure 3f). Ponderosa pine grew through the vegetation between years 5 and 10, and there was almost no overtopping of that species at the ICHwk2 site in year 10 or year 16. At the SBSmw location, approximately 20% of ponderosa pine were overtopped in years 3 and 5, but none were overtopped in years 10 or 16. There was no overtopping of ponderosa pine at the SBPSxc installation.

3 .2 Damage and 3.2.1 Hare and frost damage Browsing and clipping by hares was common Damaging Agents in at the ICHwk2 site; in year 1, hare damage affected 10−11% of surviving Sibe- Years 1−16 rian larch, Douglas-fr, and ponderosa pine, and 2−4% of lodgepole pine, western larch, and hybrid spruce (Figure 4a). In year 3 at this installation, hare damage affected 77% of surviving ponderosa pine, 47% of western larch, 40% of lodgepole pine, 36% of Douglas-fr, 16% of Siberian larch, and 15% of hybrid spruce. Hare damage in years 1 and 3 was minor at the ESSFwk1 and SBPSxc sites, affecting ≤ 5% of trees regardless of species. No hare damage was recorded at the SBSmw installation in year 1 or year 3. At the end of the frst growing season, frost damage affected 2% of surviving Siberian larch and 10% of surviving Douglas-fr at the SBSmw site (Figure 4b). At the SBPSxc site, frost damage affected 19% of surviving Siberian larch and 1% of surviving Douglas-fr at the end of the frst growing season. No year 1 frost damage was observed at other installations or among other species. There was almost no recorded frost damage to trees of any species after year 1, although it may have been present but not recorded where more serious types of damage affected trees.

3.2.2 Leader damage and forking With the exception of year 3 hare damage at the ICHwk2 installation, leader injury and stem forking were the most prevalent types of damage that affected all tree species at all study sites. Western larch and Siberian larch sustained the most extensive injury (Figure 5a, b). Despite ongoing high survival and relatively good vigour at the ESSF- wk1 site, 89% of surviving western larch had some form of leader damage in year 10. The proportion of trees with leader damage declined to 38% by year 16 at this location, but 69% of surviving larch had forked stems in year 16. At the SBPSxc installation, all western larch that survived to year 16 had leader damage and stem forks. Siberian larch sustained similar amounts of leader and forking damage as western larch at the ICHwk2 and SBSmw sites but was less affected than western larch at the ESSFwk1 location. At the SBPSxc

12 (a) Hare damage

0 Proportion of trees (%) Yr1 Yr3 Yr1 Yr3 Yr1 Yr3 Yr1 Yr3 Yr1 Yr3 Yr1 Yr3

Western Siberian Lodgepole Douglas- Hybrid Ponderosa larch larch pine fir spruce pine ICHwk2 (b) Frost damage

20 15

10 5

0 Proportion of trees (%) SBSmw SBPSxc SBSmw SBPSxc

Siberian Douglas- larch fir

 4 Proportion of (a) live trees of all species affected by hare damage in years 1 and 3 (1989) at the ICHwk2 site only (occurrence of hare damage was minor at other sites), and (b) live Siberian larch and Douglas-fir affected by frost damage in year 1 at the SBSmw and SBPSxc sites (these species did not sustain frost damage at other sites, nor was it recorded for other species at any sites). Moribund trees are not included. installation, surviving Siberian larch also sustained slightly less forking damage than western larch. Ponderosa pine was also severely affected by leader damage and/or forking at the SBPSxc site, where 73% of survivors were forked in year 16 (Figure 5f). Year 16 damage was not summarized for Douglas-fr at the SBPSxc site (Figure 5d), where nearly all the trees were moribund; however, severe forking is assumed to have occurred based on the average year 22 height of 22 cm. Douglas-fr and ponderosa pine sustained considerably less leader and forking damage at the ICHwk2 and SBSmw sites than at the SBPSxc installation, with a maximum of 31% of Douglas-fr and 22% of ponderosa pine having forks at age 16. Lodgepole pine and hybrid spruce had more prevalent forking than leader damage (Figure 5c, e). In year 16, 23% of lodgepole pine at the ICHwk2 site and 35−41% at the other locations had forks. Hybrid spruce had more extensive year 16 forking damage at the ICHwk2 (25%) and SBSmw (41%) sites than at the ESSFwk1 installation (13%).

3.2.3 Species-specific damaging agents In year 16, the proportion of live lodgepole pine that had western gall rust (Endocronartium harknessii) stem infection ranged from 6 to 10% at the ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites (Figure 6a). The proportion of live lodgepole pine that had

13 16 16 16 10 10 10 5 5 5 SBPSxc SBPSxc SBPSxc 3 3 3 1 1 1 16 16 16 10 10 10 5 5 5 SBSmw SBSmw SBSmw 3 3 3 1 1 1 16 16 16 10 10 10 Survival 5 5 5 ICHwk2 ICHwk2 ICHwk2 3 3 3 1 1 1 0 0 0

80 60 40 20 80 60 40 20 80 60 40 20

100 100 100 Proportion of trees (%) trees of Proportion (%) trees of Proportion (%) trees of Proportion (d) Douglas-fir (e) Hybrid spruce (f) Ponderosa pine Forked stem 16 16 16 10 10 10 5 5 5 SBPSxc SBPSxc SBPSxc 3 3 3 Leader damage 1 1 1 16 16 16 10 10 10 5 5 5 ESSFwk1 ESSFwk1 ESSFwk1 3 3 3 1 1 1 16 16 16 10 10 10 5 5 5 SBSmw SBSmw SBSmw 3 3 3 1 1 1 16 16 16 10 10 10 5 5 5 ICHwk2 ICHwk2 ICHwk2 3 3 3 Survival and proportion of live (a) western larch, (b) Siberian larch, (c) lodgepole pine, (d) Douglas-fir, (e) hybrid spruce, and (f) ponderosa pine with (c) lodgepole pine, (d) Douglas-fir, (b) Siberian larch, Survival and proportion of live (a) western larch, leader or stem damage in years 1 (1987), 3 (1989), 5 (1991), 10 (1996), and 16 (2002) at individual sites. Moribund trees were not included. 1 1 1

0 0 0

80 60 40 20 80 60 40 20 80 60 40 20

100 100 100 Proportion of trees (%) trees of Proportion (%) trees of Proportion (%) trees of Proportion 5   (a) Western larch (a) Western (b) Siberian larch (c) Lodgepole pine

14 western gall rust branch infections was more variable, increasing in the order of ICHwk2 (1%) < SBPSxc (18%) < ESSFwk1 (21%) < SBSmw (40%). No ponderosa pine had western gall rust stem infection in year 16, and minor branch infection (3% of live trees) was observed only at the SBSmw site. In year 16, pine needle cast (Lophodermella concolor) infection was recorded on 8% and 10% of live lodgepole pine at the ESSFwk1 and SBPSxc installations, respectively, but was not observed on lodgepole pine at the ICHwk2 or SBSmw locations (Figure 6b). In contrast, pine needle cast affected 35% and 55% of ponderosa pine at the ICHwk2 and SBSmw sites, respectively, at age 16 but was not observed on trees at the SBPSxc installation. Cooley gall adelgid branch galls (Adelges cooleyi) were present on 92%, 95%, and 68% of live hybrid spruce at the ICHwk2, SBSmw, and ESSFwk1 sites, respectively, in year 16 (Figure 6c), but they did not substantially reduce tree vigour. (a) Western gall rust Stem Branch 50 40 30 20 10 0 Proportion of trees (%) ICHwk2 SBSmw ESSFwk1 SBPSxc ICHwk2 SBSmw SBPSxc

Lodgepole Ponderosa pine pine (b) Pine needle cast

60 50 40 30 20 10 0 Proportion of trees (%) ICHwk2 SBSmw ESSFwk1 SBPSxc ICHwk2 SBSmw SBPSxc

Lodgepole Ponderosa pine pine (c) Cooley gall adelgid 100 80 60 40 20 0 Proportion of trees (%) ICHwk2 SBSmw ESSFwk1

Hybrid spruce

 6 Year 16 (2002) proportion of live (a) lodgepole pine and ponderosa pine with western gall rust stem or branch infections, (b) lodgepole pine and ponderosa pine with pine needle cast, and (c) hybrid spruce with cooley gall adelgid branch galls at individual sites. Moribund trees are not included.

15 3 .3 Growth There were signifcant overall interactions between site and species for all growth measures that were assessed, in all assessment years (Table 4). When individual pairs of sites were compared, the site × species interaction for height was most consistently signifcant for ICHwk2 versus SBSmw, ICHwk2 versus SBPSxc, and SBSmw versus ESSFwk1. For diameter, the interaction was most consistently signifcant for ICHwk2 versus SBSmw, ICHwk2 versus ESSFwk1, and SBSmw versus ESSFwk1. Site × species interactions for height growth during the year 10−16 interval were variably signifcant for the six pairwise comparisons. During the year 16−22 interval, height growth interactions were signifcant for all pairwise comparisons, and for the year 21−22 interval, they were signifcant for all comparisons except ICHwk2 versus SBSmw. Diameter growth interactions were variable; they became signifcant over time for some pairwise comparisons but non-signifcant for others. Stem volume and volume growth interactions were signifcant for all pairwise comparisons except ICHwk2 versus SBPSxc.

TABLE 4 p-valuesa indicating statistical significance of interactionsb between site and species for size and growth variables between year 3 (1989) and year 22 (2008)

Site × species interactionsc ICHwk2 vs ICHwk2 vs ICHwk2 vs SBSmw vs SBSmw vs ESSFwk1 vs Variable Year Overall SBSmw ESSFwk1 SBPSxc ESSFwk1 SBPSxc SBPSxc Height 3 < 0.01 < 0.01 0.02 < 0.01 0.07 < 0.01 0.26 5 < 0.01 < 0.01 0.20 < 0.01 0.02 < 0.01 0.48 10 < 0.01 < 0.01 0.68 < 0.01 < 0.01 < 0.01 0.02 16 < 0.01 < 0.01 0.50 0.02 < 0.01 0.11 0.02 22 < 0.01 < 0.01 0.01 0.03 < 0.01 0.26 < 0.01 Diameter 3 < 0.01 < 0.01 0.11 < 0.01 0.02 < 0.01 0.88 5 < 0.01 < 0.01 < 0.01 0.01 0.03 < 0.01 0.09 10 < 0.01 < 0.01 < 0.01 0.07 < 0.01 0.02 < 0.01 16 < 0.01 < 0.01 < 0.01 0.71 < 0.01 0.75 0.10 22 < 0.01 < 0.01 < 0.01 0.01 0.01 0.16 0.33 Volume 16 < 0.01 < 0.01 < 0.01 0.08 0.02 < 0.01 < 0.01 22 < 0.01 < 0.01 < 0.01 0.22 0.01 < 0.01 < 0.01 Height growth 10–16 < 0.01 < 0.01 0.02 0.82 < 0.01 0.17 0.02 16–22 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 21–22 < 0.01 0.77 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 Diameter growth 10–16 < 0.01 < 0.01 < 0.01 0.65 < 0.01 0.78 < 0.01 16–22 < 0.01 0.27 < 0.01 < 0.01 0.24 < 0.01 0.61 Volume growth 16–22 < 0.01 0.02 < 0.01 0.26 < 0.01 0.02 < 0.01 a Interactions are considered signifcant at p ≤ 0.05 (indicated by bold font). Owing to the absence of some zone−species combinations, the number of degrees of freedom is not the same for each comparison presented in this table. b A signifcant interaction implies that growth trends for conifer species are not parallel, while non-signifcant interactions imply parallel growth trends. c For the overall site × species interaction, due to incompleteness the denominator degrees of freedom = 12, rather than 15 as would be the case for a design where all 24 species–site combinations are represented. For contrasts testing the site × species interaction for each pair of sites, the denominator degrees of freedom for each pair of sites = number of species common to the two sites minus 1.

16 3.3.1 Between-site comparison of size and growth rates for individual species

Western larch In all assessment years, western larch was signifcantly taller at the ESSFwk1, SBSmw, and ICHwk2 sites than at the SBPSxc installation (Table 5). Western larch height was statistically similar at the ESSFwk1, SBSmw, and ICHwk2 locations in years 3, 5, and 10, but in years 16 and 20, trees were signifcantly taller at the ESSFwk1 than the ICHwk2 site. Western larch height growth during the year 10−16, 16−22, and 21−22 intervals was also signifcantly greater at the ESSFwk1, SBSmw, and ICHwk2 sites than at the SBPSxc installation (Table 6). Western larch at the ESSFwk1 site had signifcantly greater height

TABLE 5 Site effects on meana height of individual tree species in year 3 (1989), year 5 (1991), year 10 (1996), year 16 (2002), and year 22 (2008)

Height (cm) Species Year ICHwk2 SBSmw ESSFwk1 SBPSxc p-valueb Western larch 3 57 ± 6 a 78 ± 6 a 53 ± 6 a 10 ± 6 b 0.0002 5 89 ± 8 a 124 ± 8 a 93 ± 8 a 22 ± 9 b 0.0002 10 245 ± 16 a 287 ± 17 a 308 ± 16 a 40 ± 20 b < 0.0001 16 503 ± 21 b 538 ± 22 ab 601 ± 19 a 76 ± 38 c < 0.01 22 709 ± 31 b 789 ± 32 ab 908 ± 27 a 72 ± 42 c < 0.0001 Siberian larch 3 54 ± 6 ab 84 ± 6 a 63 ± 6 a 30 ± 6 b 0.002 5 85 ± 10 bc 138 ± 11 a 98 ± 10 ab 45 ± 11 c 0.002 10 230 ± 19 a 291 ± 19 a 259 ± 19 a 74 ± 19 b 0.0002 16 493 ± 26 b 618 ± 26 a 539 ± 26 ab 157 ± 28 c < 0.01 22 745 ± 30 a 886 ± 30 a 793 ± 29 a 192 ± 31 b < 0.0001 Lodgepole pine 3 36 ± 6 bc 81 ± 6 a 59 ± 6 ab 30 ± 6 c 0.001 5 88 ± 11 bc 162 ± 11 a 123 ± 11 ab 58 ± 11 c 0.001 10 303 ± 18 b 422 ± 19 a 339 ± 19 ab 150 ± 18 c < 0.0001 16 598 ± 23 b 745 ± 24 a 639 ± 24 ab 266 ± 23 c < 0.01 22 893 ± 29 a 1008 ± 30 a 912 ± 31 a 375 ± 29 b < 0.0001 Douglas-frc 3 29 ± 3 a 39 ± 3 a 14 ± 3 b 0.003 5 55 ± 6 a 69 ± 6 a 20 ± 6 b 0.002 not 10 184 ± 15 a 198 ± 15 a 30 ± 17 b 0.0004 included 16 457 ± 34 471 ± 33 – 0.79 22 726 ± 35 a 749 ± 34 a 22 ± 60 b < 0.0001 Hybrid spruce 3 45 ± 3 50 ± 3 46 ± 3 0.53 5 72 ± 6 80 ± 6 82 ± 6 0.48 not 10 149 ± 10 152 ± 11 190 ± 10 0.06 included 16 324 ± 22 307 ± 22 358 ± 22 0.30 22 553 ± 31 475 ± 31 576 ± 31 0.13 Ponderosa pine 3 20 ± 2 b 56 ± 2 a 23 ± 2 b < 0.0001 5 42 ± 3 b 105 ± 3 a 43 ± 2 b < 0.0001 not 10 161 ± 8 b 257 ± 7 a 95 ± 7 c < 0.0001 included 16 380 ± 16 b 505 ± 16 a 170 ± 31 c < 0.01 22 631 ± 21 b 745 ± 20 a 157 ± 32 c < 0.0001 a Values are mean ± 1 standard error. b p-values are based on ANOVA (p-values ≤ 0.05 are in bold typeface). Means assigned the same letter do not differ signifcantly according to the Bonferroni test. c Year 16 values are not presented for Douglas-fr at the SBPSxc site because all trees were moribund (and therefore were not included in the analysis).

17 TABLE 6 Site effects on meana height and diameter growth of individual species for year 10−16, 16−22, and 21−22 intervals

Height or diameter growth (cm) Variable Species Year ICHwk2 SBSmw ESSFwk1 SBPSxc p-valueb Height growth Western larch 10–16 227 ± 11 b 241 ± 12 ab 288 ± 9 a 23 ± 21 c < 0.01 16–22 228 ± 9 b 243 ± 9 b 306 ± 7 a 13 ± 13 c < 0.01 21–22 43 ± 2 b 42 ± 2 b 53 ± 1 a 7 ± 3 c < 0.01 Siberian larch 10–16 260 ± 12 b 324 ± 12 a 273 ± 12 ab 73 ± 13 c < 0.01 16–22 247 ± 10 a 267 ± 10 a 250 ± 10 a 50 ± 10 b < 0.01 21–22 52 ± 2 a 53 ± 2 a 46 ± 2 a 10 ± 2 b < 0.01 Lodgepole pine 10–16 293 ± 6 a 319 ± 7 a 299 ± 7 a 111 ± 6 b < 0.01 16–22 285 ± 8 a 268 ± 9 a 273 ± 9 a 119 ± 8 b < 0.01 21–22 47 ± 2 a 47 ± 2 a 49 ± 2 a 25 ± 2 b < 0.01 Douglas-fr 10–16 267 ± 19 269 ± 18 – 0.93 not 16–22 267 ± 11 a 281 ± 10 a –9 ± 23 b < 0.01 included 21–22 47 ± 2 a 45 ± 2 a 2 ± 4 b < 0.01 Hybrid spruce 10–16 176 ± 12 150 ± 12 167 ± 12 0.38 not 16–22 229 ± 12 176 ± 12 218 ± 12 0.05c included 21–22 46 ± 2 42 ± 2 43 ± 2 0.37 Ponderosa pine 10–16 218 ± 6 a 240 ± 6 a 47 ± 17 b < 0.01 not 16–22 251 ± 10 a 246 ± 9 a 33 ± 15 b < 0.01 included 21–22 44 ± 3 a 40 ± 3 a 9 ± 3 b < 0.01 Diameter growthd Western larch 10–16 7.9 ± 0.4 b 9.4 ± 0.4 a 6.3 ± 0.3 c 2.6 ± 0.8 d < 0.01 16–22 3.2 ± 0.2 a 2.7 ± 0.2 b 3.7 ± 0.2 a – < 0.01 Siberian larch 10–16 9.8 ± 0.3 b 12.1 ± 0.3 a 11.9 ± 0.3 a 4.1 ± 0.3 c < 0.01 16–22 2.9 ± 0.2 2.3 ± 0.2 2.7 ± 0.2 1.9 ± 0.2 0.05c Lodgepole pine 10–16 10.0 ± 0.6 b 13.2 ± 0.7 ab 14.5 ± 0.7 a 5.4 ± 0.6 c < 0.01 16–22 2.6 ± 0.2 b 2.6 ± 0.2 b 3.5 ± 0.2 a 2.5 ± 0.2 b 0.01 Douglas-fre 10–16 8.8 ± 0.4 9.0 ± 0.4 not – 0.68 16–22 3.7 ± 0.2 3.3 ± 0.2 included – 0.23 Hybrid spruce 10–16 6.8 ± 0.5 6.5 ± 0.5 7.6 ± 0.5 not 0.36 16–22 3.7 ± 0.2 3.0 ± 0.2 3.5 ± 0.2 included 0.11 Ponderosa pine 10–16 10.3 ± 0.4 b 13.5 ± 0.3 a not 5.6 ± 1.0 c < 0.01 16–22 4.4 ± 0.3 a 3.4 ± 0.3 ab included 1.6 ± 0.5 b 0.01 a Values are mean ± 1 standard error. b p-values are based on ANOVA (p-values ≤ 0.05 are in bold typeface). Means assigned the same letter do not differ signifcantly according to the Bonferroni test. c Indicates the Bonferroni test could not separate means although p ≤ 0.05. d Diameter growth is based on ground-level diameter for the year 10–16 interval and on diameter at 1.3 m (dbh) for the year 16–22 interval. e Values are not presented for Douglas-fr at the SBPSxc site because all trees were moribund in years 16 and 22 (and therefore were not included in the analysis).

growth than those at the ICHwk2 site during the year 10−16, 16−22, and 21−22 intervals, and ESSFwk1 larch also had signifcantly greater height growth than SBSmw larch during the year 16−22 and 21−22 intervals. In all assessment years, western larch was signifcantly larger in diameter at the ESSFwk1, SBSmw, and ICHwk2 sites than at the SBPSxc installation (Table 7). In years 3 and 5, western larch at the SBSmw site had signifcantly larger diameter than at the ESSFwk1 or ICHwk2 sites. By year 10, diameter

18 TABLE 7 Site effects on meana ground-level diameter (gld) in year 3 (1989), year 5 (1991), year 10 (1996), and year 16 (2002), and mean diameter at 1.3 m (dbh) in year 22 (2008)

Diameter (cm) Species Year ICHwk2 SBSmw ESSFwk1 SBPSxc p-valueb Western larch 3 0.91 ± 0.08 bc 1.35 ± 0.08 a 0.89 ± 0.08 b 0.40 ± 0.08 d 0.0003 5 1.41 ± 0.13 bc 2.45 ± 0.13 a 1.75 ± 0.13 b 0.66 ± 0.13 d 0.0001 10 3.70 ± 0.30 b 5.71 ± 0.33 a 6.89 ± 0.29 a 1.15 ± 0.30 c < 0.0001 16 8.4 ± 0.5 b 9.9 ± 0.5 b 13.3 ± 0.4 a 2.7 ± 0.9 c < 0.01 22 8.2 ± 0.5 b 9.2 ± 0.5 b 12.3 ± 0.4 a 1.2 ± 2.3 c < 0.0001 Siberian larch 3 0.90 ± 0.11 b 1.57 ± 0.11 a 1.08 ± 0.11 ab 0.60 ± 0.11 b 0.002 5 1.50 ± 0.19 bc 2.77 ± 0.19 a 2.33 ± 0.19 ab 1.09 ± 0.19 c 0.001 10 4.41 ± 0.39 b 6.74 ± 0.40 a 5.76 ± 0.39 ab 1.95 ± 0.40 c 0.0001 16 10.3 ± 0.3 b 12.7 ± 0.4 a 12.4 ± 0.3 a 4.3 ± 0.4 c < 0.01 22 9.9 ± 0.3 a 10.9 ± 0.3 a 10.6 ± 0.3 a 2.6 ± 0.4 b < 0.0001 Lodgepole pine 3 0.91 ± 0.13 b 1.75 ± 0.13 a 1.26 ± 0.13 ab 0.85 ± 0.13 b 0.003 5 1.91 ± 0.24 b 3.45 ± 0.25 a 3.37 ± 0.25 a 1.60 ± 0.24 b 0.001 10 5.84 ± 0.33 b 8.25 ± 0.34 a 8.65 ± 0.35 a 3.20 ± 0.33 c < 0.0001 16 10.6 ± 0.7 b 14.0 ± 0.7 a 15.4 ± 0.7 a 5.7 ± 0.7 c < 0.01 22 10.5 ± 0.5 b 12.8 ± 0.6 ab 14.3 ± 0.6 a 5.8 ± 0.5 c < 0.0001 Douglas-frc 3 0.64 ± 0.04 b 0.83 ± 0.04 a 0.46 ± 0.05 b 0.003 5 1.05 ± 0.09 b 1.55 ± 0.09 a 0.79 ± 0.10 b 0.002 not 10 3.72 ± 0.27 a 4.31 ± 0.27 a 1.27 ± 0.30 b 0.0004 included 16 9.2 ± 0.4 9.5 ± 0.4 – 0.64 22 9.2 ± 0.4 8.9 ± 0.3 – 0.56 Hybrid spruce 3 0.93 ± 0.04 0.98 ± 0.04 0.96 ± 0.04 0.72 5 1.54 ± 0.10 1.71 ± 0.11 1.91 ± 0.10 0.11 not 10 3.36 ± 0.21 b 3.24 ± 0.21 b 4.35 ± 0.21 a 0.02 included 16 7.2 ± 0.5 6.9 ± 0.5 8.1 ± 0.5 0.32 22 7.7 ± 0.5 6.6 ± 0.5 8.2 ± 0.5 0.17 Ponderosa pine 3 0.78 ± 0.04 b 1.58 ± 0.04 a 0.93 ± 0.04 b < 0.0001 5 1.25 ± 0.07 c 2.89 ± 0.07 a 1.65 ± 0.06 b < 0.0001 not 10 4.49 ± 0.16 b 7.53 ± 0.15 a 3.40 ± 0.16 c < 0.0001 included 16 10.6 ± 0.4 b 14.3 ± 0.4 a 5.7 ± 1.0 c < 0.01 22 11.2 ± 0.7 a 12.9 ± 0.7 a 3.3 ± 1.2 b 0.0009 a Values are mean ± 1 standard error. b p-values are based on ANOVA (p-values ≤ 0.05 are in bold typeface). Means assigned the same letter do not differ signifcantly according to the Bonferroni test. c Year 16 values are not presented for Douglas-fr at the SBPSxc site because all trees were moribund (and therefore were not included in the analysis); year 22 values are not presented because trees had not achieved a height of 1.3 m (dbh).

was signifcantly larger at the ESSFwk1 and SBSmw locations than at the ICHwk2 (Table 7). In years 16 and 22, diameter at the ESSFwk1 site signifcantly exceeded diameter at the SBSmw and ICHwk2 locations. Diameter growth during the year 10−16 interval decreased signifcantly at the four sites in the order of SBSmw > ICHwk2 > ESSFwk1 > SBPSxc (Table 6). For the year 16−22 interval, western larch diameter growth was signifcantly greater at the ESSFwk1 and ICHwk2 installations than at the SBSmw location (the SBPSxc site was not included in the comparison because most trees had not achieved a height of 1.3 m in year 16). Western larch mean stem volume in years 16 and 22 was signifcantly greater at the ESSFwk1 site than at the ICHwk2 or SBSmw locations (Table 8). Mean

19 TABLE 8 Site effects on meana stem volume (dm3)b for individual tree species in years 16 (2002) and 22 (2008), and volume growth from years 16–22

Volume (dm3/tree) Species Year ICHwk2 SBSmw ESSFwk1 SBPSxc p-valuec Western larch 16 8.0 ± 1.1 b 9.1 ± 1.1 b 15.2 ± 0.8 a 0.2 ± 8.8 ab < 0.01 22 27.4 ± 2.9 b 25.8 ± 3.0 b 45.9 ± 2.3 a 0.1 ± 14.1 b < 0.01 16–22 20.0 ± 2.0 b 16.3 ± 2.0 b 31.0 ± 1.5 a – < 0.01 Siberian larch 16 9.4 ± 1.3 a 15.2 ± 1.4 a 12.8 ± 1.3 a 0.1 ± 1.7 b < 0.01 22 26.7 ± 2.4 a 34.5 ± 2.5 a 32.6 ± 2.3 a 0.8 ± 3.0 b < 0.01 16–22 17.1 ± 1.3 a 19.2 ± 1.4 a 19.5 ± 1.3 a 0.9 ± 1.9 b < 0.01 Lodgepole pine 16 16.2 ± 2.1 b 29.8 ± 2.2 a 28.1 ± 2.2 a 1.5 ± 2.1 c < 0.01 22 43.7 ± 4.5 b 64.1 ± 4.7 ab 70.3 ± 4.8 a 5.7 ± 4.5 c < 0.01 16–22 27.0 ± 2.5 b 34.7 ± 2.6 ab 42.1 ± 2.7 a 4.4 ± 2.5 c < 0.01 Douglas-frd 16 6.3 ± 1.1 6.6 ± 1.0 – 0.81 not 22 24.4 ± 2.0 23.5 ± 1.8 – 0.75 included 16–22 18.0 ± 1.3 17.1 ± 1.2 – 0.64 Hybrid spruce 16 2.5 ± 0.4 2.3 ± 0.4 4.1 ± 0.4 0.05e not 22 13.6 ± 1.9 9.7 ± 1.9 17.6 ± 1.9 0.07 included 16–22 11.3 ± 1.5 7.8 ± 1.5 13.6 ± 1.5 0.08 Ponderosa pine 16 6.7 ± 1.2 b 15.8 ± 1.2 a 0.6 ± 2.7 b < 0.01 not 22 28.7 ± 3.9 a 42.4 ± 3.8 a 1.4 ± 6.7 b < 0.01 included 16–22 22.0 ± 2.9 a 27.1 ± 2.8 a 1.3 ± 5.2 b < 0.01 a Values are mean ± 1 standard error. b Stem volume is calculated using Kozak (1988) taper equations. One cubic decimeter (dm3) = 1000 cm3 = 0.001 m3. c p-values are based on ANOVA (p-values ≤ 0.05 are in bold typeface). Means assigned the same letter do not differ signifcantly according to the Bonferroni test. d Values cannot be presented for Douglas-fr at the SBPSxc site because trees had not achieved a height of 1.3 m (dbh). e Indicates the Bonferroni test could not separate means although p ≤ 0.05.

stem volume was highly variable at the SBPSxc site; consequently, although means were very small, the Bonferroni test could not consistently separate them from larger, less variable means at the other locations. Year 16−22 volume growth was signifcantly larger at the ESSFwk1 than the ICHwk2 or SBSmw sites. Year 16−22 volume growth was not calculated for the SBPSxc installation due to a mean overall decrease in size between years 16 and 22.

Siberian larch In all assessment years, Siberian larch height was statistically similar at the SBSmw and ESSFwk1 sites, and height at both locations signifcantly exceeded that at the SBPSxc installation (Table 5). In years 10, 16, and 22, Siberian larch at the ICHwk2 site was also signifcantly taller than that at the SBPSxc installation. In years 5 and 16, Siberian larch was signifcantly taller at the SBSmw than the ICHwk2 site. For the year 10−16 interval, Siberian larch height growth was signifcantly greater at the SBSmw installation than at the ICHwk2 or SBPSxc sites (Table 6). During the year 16−22 and year 21−22 intervals, height growth was statistically similar at the ICHwk2, SBSmw, and ESSFwk1 installations, all of which signifcantly exceeded that at the SBPSxc site. Siberian larch had signifcantly larger diameter at the SBSmw installation than at the ICHwk2 or SBPSxc sites in years 3, 5, 10, and 16 (Table 7). In years

20 5 through 22, diameter was also signifcantly larger at the ESSFwk1 than the SBPSxc site, and in years 10 through 22, it was larger at the ICHwk2 than the SBPSxc site. Siberian larch diameter growth from year 10 to 16 was signifcantly greater at the SBSmw and ESSFwk1 sites than at the ICHwk2 or SBPSxc sites; diameter growth at the ICHwk2 installation also signifcantly exceeded that at the SBPSxc installation (Table 6). For the year 16−22 interval, the Bonferroni test could not separate mean diameter growth despite a signifcant site effect (p = 0.05). Siberian larch stem volume in years 16 and 22 and volume growth for the year 16−22 interval were signifcantly greater at the SBSmw, ESSFwk1, and ICHwk2 sites than at the SBPSxc installation (Table 8). There were trends in greater volume and volume growth at the ESSFwk1 and SBSmw sites than at the ICHwk2 location, but means did not differ signifcantly.

Lodgepole pine In all assessment years, lodgepole pine was signifcantly taller at the SBSmw and ESSFwk1 sites than at the SBPSxc location (Table 5). In years 10 through 22, lodgepole pine height at the ICHwk2 site also signifcantly exceeded that at the SBPSxc site. Pine at the SBSmw site was signifcantly taller than that at the ICHwk2 site until year 16, but ESSFwk1 pine did not differ signifcantly in height from those at the SBSmw or ICHwk2 sites in any of the assessment years. During the year 10−16, 16−22, and 21−22 intervals, lodgepole pine height growth at the SBSmw, ICHwk2, and ESSFwk1 sites was statistically similar, and consistently exceeded that at the SBPSxc location (Table 6). Lodgepole pine had signifcantly larger diameter at the SBSmw site than at the ICHwk2 or SBPSxc installations in years 3, 5, 10, and 16 (Table 7). Pine had signifcantly larger diameter at the ESSFwk1 site than at the ICHwk2 or SBPSxc locations in years 5 through 22; and in years 10, 16, and 22, ICHwk2 pine also had signifcantly larger diameter than SBPSxc pine. Lodgepole pine diameter growth during the year 10−16 interval was signifcantly greater at the ESSFwk1, SBSmw, and ICHwk2 sites than at the SBPSxc location, and diameter growth at the ESSFwk1 site also signifcantly exceeded that at the ICHwk2 location (Table 6). During the year 16−22 interval, lodgepole pine diameter growth at the ESSFwk1 site was signifcantly greater than that at the other three locations. Lodgepole pine stem volume in years 16 and 22, and volume growth for the year 16−22 interval were signifcantly greater at the SBSmw, ESSFwk1, and ICHwk2 sites than at the SBPSxc site (Table 8). In year 16, stem volume was signifcantly larger at the SBSmw and ESSFwk1 sites than at the ICHwk2 installation; the difference between the ESSFwk1 and ICHwk2 sites persisted to year 22. Stem volume growth between years 16 and 22 was signifcantly greater at the ESSFwk1 than at the ICHwk1 site.

Douglas-fir Douglas-fr failed to increase in height at the SBPSxc site, with survivors averaging only 22 cm in height at age 22 (Table 5). Fir from this installation were not included in the analysis for year 16 because nearly all the trees were moribund; in all other assessment years, Douglas-fr was signifcantly taller at the ICHwk2 and SBSmw sites than at the SBPSxc location. Douglas-fr height did not differ signifcantly between the SBSmw and ICHwk2 sites in any of the assessment years. Height growth of Douglas-fr during the

21 year 10−16 interval was statistically similar at the ICHwk2 and SBSmw installations (the SBPSxc site could not be included due to the absence of year 16 data) (Table 6). For the year 16−22 and year 21−22 intervals, Douglas-fr height growth continued to be statistically similar at the ICHwk2 and SBSmw sites, and both were signifcantly greater than that at the SBPSxc location. In years 3 and 5, Douglas-fr at the SBSmw site had signifcantly larger diameter than those at the ICHwk2 and SBPSxc installations (Table 7). In year 10, Douglas-fr diameter at the SBSmw and ICHwk2 locations was signifcantly larger than at the SBPSxc site. In years 16 and 22, Douglas-fr diameter was statistically similar at the ICHwk2 and SBSmw sites; the SBPSxc was not included in the analysis for these years because diameter was not measured in year 16, and in year 22 trees had not achieved a height of 1.3 m. There were no signifcant differences in Douglas-fr diameter growth between the ICHwk2 and SBSmw installations for the year 10−16 and year 16−22 intervals (diameter data were not collected for Douglas-fr at the SBPSxc site in years 16 or 22) (Table 6). There were no signifcant differences in Douglas-fr stem volume in years 16 or 22, or in year 16−22 stem volume growth, between the ICHwk2 and the SBSmw sites (Table 8). Values could not be calculated for Douglas-fr at the SBPSxc location.

Hybrid spruce Hybrid spruce height did not differ signifcantly between sites in any assessment year (Table 5). The site effect on spruce height growth was not signifcant for the year 10−16 and year 21−22 intervals, and although the effect was signifcant for the year 16−22 interval (p = 0.05), the Bonferroni test could not separate means (Table 6). There were no signifcant differences in spruce diameter between installations except in year 10, when diameter was signifcantly larger at the ESSFwk1 installation than at the ICHwk2 and SBSmw sites (Table 7). There also were no signifcant differences in rates of spruce diameter growth between the three locations for the year 10−16 or year 16−22 intervals (Table 6). The site effect was signifcant for year 16 spruce stem volume (p = 0.05), but the Bonferroni test could not separate means (Table 8). The site effect on year 22 hybrid spruce stem volume and year 16−22 stem volume growth was not signifcant.

Ponderosa pine Ponderosa pine was signifcantly taller at the SBSmw site than at the ICHwk2 or SBPSxc sites in all assessment years (Table 5). In years 10, 16, and 22, height at the ICHwk2 installation also signifcantly exceeded that at the SBPSxc location. Ponderosa pine height growth for the year 10−16, 16−22, and 21−22 intervals was statistically similar at the ICHwk2 and SBSmw installations, and height growth at both locations was signifcantly greater than that at the SBPSxc site (Table 6). Ponderosa pine had signifcantly larger diameter at the SBSmw site than at the ICHwk2 or SBPSxc installations in years 3, 5, 10, and 16 (Table 7). In year 5, ponderosa pine diameter was signifcantly larger at the SBPSxc than at the ICHwk2 site, but the reverse was true in years 10 through 22. At the three sites where ponderosa pine was assessed, diameter growth for the year 10−16 interval signifcantly decreased in the order of SBSmw > ICHwk2 > SBPSxc (Table 6). During the year 16−22 interval, diameter growth was signifcantly greater at the ICHwk2 than at the SBPSxc installation.

22 In year 16, ponderosa pine stem volume was signifcantly larger at the SBSmw site than at the ICHwk2 or SBPSxc installations (Table 8). Year 22 stem volume and year 16–22 volume growth were signifcantly greater at the SBSmw and ICHwk2 sites than at the SBPSxc location.

3.3.2 Between-species size and growth rate comparison at the ICHwk2, SBSmw, and ESSFwk1 sites

ICHwk2 At the ICHwk2 site in year 22, lodgepole pine was signifcantly taller than ponderosa pine and hybrid spruce, and Siberian larch was signifcantly taller than hybrid spruce (Figure 7a). During the year 10–16 interval, height growth of lodgepole pine, Siberian larch, and Douglas-fr signifcantly exceeded that of hybrid spruce (Figure 7b). Height growth during the year 16–22 interval was signifcantly greater for lodgepole pine than hybrid spruce and western larch, but there were no other between-species differences (Figure 7c). During the year 21–22 interval, Siberian larch increased the most in height (52 cm), but the Bonferroni test was unable to separate means at p = 0.05 (Figure 7d). At age 22, ponderosa pine at the ICHwk2 site had signifcantly larger stem diameter (dbh) than Douglas-fr, western larch, or hybrid spruce, and Siberi- an larch and lodgepole pine diameter signifcantly exceeded that of hybrid spruce (Figure 8a). Between years 16 and 22, ponderosa pine increased in diameter (dbh) signifcantly more than lodgepole pine, Siberian larch, and western larch; and Douglas-fr and hybrid spruce also increased signifcantly more in diameter than lodgepole pine (Figure 8b). Year 22 stem volume at the ICHwk2 installation was signifcantly larger for lodgepole pine than Siberian larch, Douglas-fr, or hybrid spruce, but there were no other between-species differences (Figure 9a). Lodgepole pine stem volume growth for the year 16–22 interval was signifcantly greater than that of Siberian larch and hybrid spruce, and ponderosa pine volume growth was also signifcantly greater than that of hybrid spruce (Figure 9b).

SBSmw At the SBSmw site, lodgepole pine was signifcantly taller in year 22 than any other species except Siberian larch (Figure 7a). During the year 10–16 interval, height growth of lodgepole pine and Siberian larch was signifcantly greater than that of the other species, and height growth of western larch, Douglas-fr, and ponderosa pine also signifcantly exceeded that of hybrid spruce (Figure 7b). For the year 16–22 interval, hybrid spruce increased in height signifcantly less than the other species, which did not differ signifcantly from each other (Figure 7c). During the year 21–22 interval, Siberian larch increased in height by 53 cm, which was signifcantly greater than height increases for western larch, hybrid spruce, or ponderosa pine (Figure 7d). Lodgepole pine and ponderosa pine at the SBSmw site had almost identi- cal diameter (dbh) in year 22 (12.8 cm versus 12.9 cm, respectively), which signifcantly exceeded that of all other species except Siberian larch (Figure 8a). Between years 16 and 22, ponderosa pine increased in diameter (dbh) signifcantly more than Siberian larch, but there were no other between- species differences in diameter growth rate (Figure 8b). Lodgepole pine stem volume in year 22 was signifcantly larger than that of any other species at the SBSmw site (Figure 9a). In the same year, ponderosa

23 (a) p < 0.01 p < 0.01 p < 0.01 1200 a a ab a a 1000 bc a abc ab abc c c 800 bc c b 600 d

Year 22 400

height (cm ) 200 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

(b) p < 0.01 p < 0.01 p < 0.01 350 a a a b a a a 300 a a ab b b 250 ab b 200 c b 150 100 Year 10–16 50

height growth (cm ) 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

height growth (cm ) 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

(d) p = 0.05† p < 0.01 p < 0.01 60 a a ab ab ab ab b b 50 b b 40 30 20

Year 21–22 10 0 height growth (cm ) Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

 7 Comparison of (a) year 22 height, (b) year 10–16 height growth, (c) year 16–22 height growth, and (d) year 21–22 height growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites. Lw: western larch; Ls: Siberian larch; Pl: lodgepole pine; Fd: Douglas-fir; Sx: hybrid spruce; Py: ponderosa pine. For individual sites, means with the same letter do not differ significantly according to the Bonferroni test; † indicates the Bonferroni test was unable to separate means and no letters are assigned.

24 (a) p < 0.01 p < 0.01 p < 0.01 16 a a a 14 ab a ab 12 ab ab b bc bc bc 10 bc c c 8 c 6 Year 22

dbh (cm ) 4 2 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

(b) p < 0.01 p < 0.01 p = 0.02 5 a ab ab a ab ab 4 bc ab a bc ab c ab ab b 3 b 2

Year 16–22 1 dbh growth (cm ) 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

 8 Comparison of (a) year 22 dbh and (b) year 16–22 dbh growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites. Lw: western larch; Ls: Siberian larch; Pl: lodgepole pine; Fd: Douglas-fir; Sx: hybrid spruce; Py: ponderosa pine. For individual sites, means with the same letter do not differ significantly according to the Bonferroni test. pine volume was signifcantly larger than that of western larch, Douglas-fr, or hybrid spruce; Siberian larch stem volume was signifcantly larger than that of Douglas-fr or hybrid spruce; and western larch had greater volume than hybrid spruce. Lodgepole pine stem volume growth for the year 16–22 interval was signifcantly greater than that of any species except ponderosa pine (Figure 9b). Ponderosa pine volume growth for the year 16–22 interval signifcantly exceeded that of western larch and hybrid spruce, and Siberian larch volume growth during that period was also signifcantly greater than that of hybrid spruce.

ESSFwk1 In year 22, lodgepole pine and western larch were approximately the same height (912 cm versus 908 cm, respectively) at the ESSFwk1 site, and both species, as well as Siberian larch, were signifcantly taller than hybrid spruce (Figure 7a). During the year 10–16 interval, height growth of these three species was also signifcantly greater than that of hybrid spruce (Figure 7b). Between years 16 and 22, western larch and lodgepole pine continued to have signifcantly greater height growth than hybrid spruce, but Siberian larch did not (Figure 7c). During the year 21–22 interval, only western larch, which grew 53 cm, had signifcantly greater height growth than hybrid spruce (Figure 7d). Lodgepole pine diameter (dbh) in year 22 was signifcantly larger than that of Siberian larch and hybrid spruce but not western larch (Figure 8a). West- ern larch and Siberian larch also had signifcantly larger diameter than hybrid spruce in that year. Between years 16 and 22, western larch increased in diameter (dbh) signifcantly more than Siberian larch, but there were no other between-species differences in diameter growth rate (Figure 8b).

25 (a) p < 0.01 p < 0.01 p < 0.01 80 a a 70 )

3 60 50 a b b bc 40 bc ab b b ab cd de 30 c Year 22 20 b e volume (dm 10 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

(b) p < 0.01 p < 0.01 p < 0.01 ) 3 50 a a 40 a a ab 30 abc ab bc b bc abc cd bcd 20 c b d Year 16–22 10 0 volume growth (dm Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1

 9 Comparison of (a) year 22 stem volume and (b) year 16–22 stem volume growth for individual species at the ICHwk2, SBSmw, and ESSFwk1 sites. Lw: western larch; Ls: Siberian larch; Pl: lodgepole pine; Fd: Douglas-fir; Sx: hybrid spruce; Py: ponderosa pine. For individual sites, means with the same letter do not differ significantly according to the Bonferroni test.

Lodgepole pine stem volume in year 22 was signifcantly larger than that of western larch, Siberian larch, or hybrid spruce at the ESSFwk1 location (Figure 9a). Western larch also had signifcantly greater stem volume than hybrid spruce. Year 16–22 volume growth was signifcantly greater for lodgepole pine and western larch than for Siberian larch or hybrid spruce (Figure 9b).

3 .4 Stand-level 3.4.1 Year 22 tree condition according to growth and yield damage criteria Responses In year 22, forks or crooks that were serious enough to be recorded as growth and yield damage were present on all tree species at all sites, with the exception of hybrid spruce at the ICHwk2 location (Table 9). Forks and crooks were most extensive among Siberian larch (15–41% of trees damaged) and lodgepole pine (10–32% of trees damaged), with the proportion of trees that sustained damage increasing in the order of ICHwk2 < SBSmw < ESSFwk1 < SBPSxc. At the SBPSxc site, a substantial proportion of surviving ponderosa pine (22%) also had forks or crooks in year 22. The proportion of western larch that had forks or crooks ranged from 4% at the ICHwk2 installation to 12% at the ESSF- wk1 site. The incidence of forks and crooks among Douglas-fr and ponderosa pine at the ICHwk2 and SBSmw sites ranged from 2 to 9%, while 5–7% of hybrid spruce at the ICHwk2 and SBSmw sites sustained this type of damage. Fourteen percent and 25% of spruce at the ICHwk2 and SBSmw sites, respectively, had white pine terminal weevil (Pissodes strobi) damage, but spruce at the ESSFwk1 installation were unaffected (Table 9). Other types of damage recorded in the growth and yield assessment affected primarily lodgepole pine

26 TABLE 9 Proportion of live trees affected by specific damage types and damaging agents in the year 22 (2008) growth and yield assessment at the ICHwk2, SBSmw, ESSFwk1, and SBPSxc sitesa

Proportion of live trees affected (%) Damaging agent

Damage type

Species Site or Fork crook Scar Dead top Mistletoe Ungulate Squirrel Mountain beetlepine gall rust Western infection stem gall rust Western infection branch Lodgepole pine weevilterminal pine White weevilterminal Snow/ice competition Tree Unknown Western larch ICHwk2 4 2 – – 1 – – – – – – – – – SBSmw 6 – – – – – – – – – – – – 3 ESSFwk1 12 1 – – – – – – – – – – – – SBPSxc 6 – – – – – – – – – – – – – Siberian larch ICHwk2 15 1 – – – – – – – – – – – 2 SBSmw 19 – – – – – – – – – – – 1 – ESSFwk1 19 – – – – – – – – – – – – – SBPSxc 41 – – – – – – – – – – – – – Lodgepole pine ICHwk2 10 10 – – 2 – – 10 5 – – – – – SBSmw 17 13 – – – 1 – 12 12 1 – – – 3 ESSFwk1 17 6 – – – – – – – – – – – SBPSxc 32 19 – 4 – – 9 22 16 – – – – 2 Douglas-fr ICHwk2 2 – – – – – – – – – – – – – SBSmw 3 – – – 2 – – – – – – – – – Hybrid spruce ICHwk2 – – – – – – – – – 14 – – – SBSmw 7 – – – – – – – – – 25 – 1 – ESSFwk1 5 – 1 – – – – – – – – – – – Ponderosa pine ICHwk2 4 2 – – 4 – – – – – – – – – SBSmw 9 1 – – – – – 1 2 – – 3 – 1 SBPSxc 22 1 – – – – – 2 1 – – – – 1 a Moribund trees were not included in the summary; all surviving Douglas-fr at the SBPSxc site were moribund in year 22.

and not other species. Up to 19% of lodgepole pine had scars that were serious enough to be recorded in the growth and yield assessment, whereas scarring affected no more than 2% of trees of other species at any of the locations. Scar- ring of lodgepole pine was least severe at the ESSFwk1 site, where only 6% of trees were damaged. For lodgepole pine at the ICHwk2, SBSmw, and SBPSxc sites, western gall rust stem infections were recorded on 10–22% of trees, while branch infections were recorded on 5–16% of trees; galls were not observed on pine at the ESSFwk1 installation (Table 9). Ponderosa pine is also susceptible to western gall rust, but only 1–2% of surviving trees were affected at any site. At the SBPSxc site, 9% of lodgepole pine were damaged by the mountain pine beetle (Dendroctonus ponderosae), but otherwise, both lodgepole and ponderosa pine were unaffected by the beetle as of year 22. Animal, abiotic, and unknown damage also affected a minor proportion of trees (Table 9).

3.4.2 Gross stand volume per hectare Year 22 stand volume for individual species ranged from 24 to 109 m3/ha at the ICHwk2, SBSmw, and ESSFwk1 sites; at the SBPSxc installation, stand volume was 12 m3/ha for lodgepole pine and less than 1 m3/ha for other species (Figure 10). In year 22, lodgepole

27 p < 0.01 p < 0.01 p < 0.01 p < 0.01 140

a 120 a a

/ha) 100 ab 3

80 b bc b 60 b b bc c b b b c 40 c

Gross volume (m 20 a b b b 0 Lw Ls Pl Fd Sx Py Lw Ls Pl Fd Sx Py Lw Ls Pl Sx Lw Ls Pl Sx

ICHwk2 SBSmw ESSFwk1 SBPSxc

 10 Comparison of year 22 gross stand volume per hectare for individual species at the ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites. Lw: western larch; Ls: Siberian larch; Pl: lodgepole pine; Fd: Douglas-fir; Sx: hybrid spruce; Py: ponderosa pine. For individual sites, means with the same letter do not differ significantly according to the Bonferroni test.

pine had signifcantly greater stand volume than any other species at the ICHwk2 and SBSmw sites; at the ESSFwk1 installation, it had greater stand volume than all species but western larch. At the ICHwk2 site, species other than lodgepole pine had statistically similar stand volume. At the SBSmw site, Siberian larch had signifcantly greater stand volume than western larch and hybrid spruce, and at the ESSFwk1 installation, western larch had signifcantly greater stand volume than hybrid spruce. When year 22 stand volume achieved by individual species was compared between locations, no signifcant differences between sites were evident for Siberian larch, lodgepole pine, Douglas-fr, or hybrid spruce (Figure 11). Western larch had signifcantly greater stand volume at the ESSFwk1 site than at the ICHwk2 or SBSmw installations and ponderosa pine had signifcantly greater stand volume at the SBSmw site than at the ICHwk2 location.

3.4.3 Site index ANOVA was not conducted for site index; however, mean values for individual sites are presented in Table 10. At the ICHwk2 installation, there was a trend of higher site index for Douglas-fr and western larch (24.7 m and 23.5 m, respectively) than for other species, for which site index ranged from 20.2 m (ponderosa pine) to 21.6 m (Siberian larch). At the SBSmw location, Douglas-fr again had the highest mean site index (23.8 m), and values for the other species descended in the order of Siberian larch (22.0 m) > lodgepole pine (21.5 m) > ponderosa pine (21.1 m) > western larch (20.5 m) > hybrid spruce (19.5 m). At the ESSFwk1 installation, mean site index was highest for western larch (22.4 m) and Siberian larch (21.6 m), followed by lodgepole pine (21.1 m) and hybrid spruce (21.0 m). Site index at the SBPSxc site decreased in the order of lodgepole pine (14.0 m) > Siberian larch (13.6 m) > western larch (13.4 m) > ponderosa pine (10.4 m). Site index could not be determined for Douglas-fr at that location because none had achieved a height of 1.3 m by age 22.

28 p = 0.0004 p = 0.112 p = 0.787 p = 0.470 p = 0.080 p = 0.030 140

120 a

/ha) 100

3 a 80

60 b b b 40

Gross volume (m 20

0 SBSmw SBSmw SBSmw SBSmw SBSmw SBSmw ICHwk2 ICHwk2 ICHwk2 ICHwk2 ICHwk2 ICHwk2 ESSFwk1 ESSFwk1 ESSFwk1 ESSFwk1 Western larch Siberian larch Lodgepole pine Douglas-fir Hybrid spruce Ponderosa pine

 11 Comparison of year 22 gross stand volume per hectare at ICHwk2, SBSmw, and ESSFwk1 sites for western larch, Siberian larch, lodgepole pine, Douglas-fir, hybrid spruce, and ponderosa pine. For individual sites where p ≤ 0.05, means with the same letter do not differ significantly according to the Bonferroni test (no letters are assigned where p > 0.05).

TABLE 10 Meana year 22 site index estimated from year 22 tree size for individual tree species at the ICHwk2, SBSmw1, ESSFwk1, and SBPSxc sites

Site Index (m) Species ICHwk2 SBSmw ESSFwk1 SBPSxc Western larch 23.5 ± 0.5 20.5 ± 0.4 22.4 ± 0.5 13.4 ± 0.9b Siberian larch 21.6 ± 1.0 22.0 ± 0.4 21.6 ± 0.4 13.6 ± 0.7 Lodgepole pine 21.4 ± 0.5 21.5 ± 0.3 21.1 ± 0.2 14.0 ± 0.2 Douglas-fr 24.7 ± 1.5 23.8 ± 0.3 – – Hybrid spruce 20.9 ± 0.9 19.5 ± 0.5 21.0 ± 0.5 – Ponderosa pine 20.2 ± 0.3 21.1 ± 0.3 – 10.4 ± 0.9 a Values are mean ± 1 standard error. b The site index value for western larch at the SBPSxc site is based on only two site trees.

4 DISCUSSION Experimental Project 904.02 examines survival and growth performance of western larch, Siberian larch, and ponderosa pine relative to that of naturally occurring conifers in the Cariboo Region. The study was established in 1987, prior to widespread acceptance of climate change as a serious threat to forest health in British Columbia. Since that time, various strategies to mitigate the potential negative effects of climate change and increase forest resilience have been considered. One potential strategy is the assisted migration of conifer species beyond their natural range. In order to keep pace with climate-related changes to habitat, it has been estimated that temperate tree species would have to migrate at a rate of at least 1000 m/year (Malcolm et al. 2002), whereas historical records suggest actual migration rates are in the order of 100 m/year (Aitken et al. 2008). For a variety of reasons, western larch was a good candidate for assisted migration, and recent modelling by Rehfeldt and Jaquish

29 (2010) resulted in the development of seed planning zones (designated LW1 and LW2) that make this species acceptable across a considerable portion of south−central British Columbia (B.C. Ministry of Forests, Lands and Natural Resource Operations 2014). The responses of western larch in our study are, therefore, particularly relevant to current forest management and are the focal point of this discussion. None of our study sites are precisely within the LW1 or LW2 seed planning zones (Table 2); however, we do not think this diminishes the relevance of our results. The seed planning zone boundaries are based on climate projections to 2030 coupled with current elevational deployment limits for the seed source populations, and cannot be expected to fully take into account ecosystem variation at a local scale. Our experiment was conducted in four biogeoclimatic subzones or variants that occupy relatively large areas in the Cariboo Region. To the east of the Fra ser River, the moist, productive ICHwk2 and SBSmw are suited to a wide range of tree species that includes lodgepole pine, Douglas-fr, and hybrid spruce, while lodgepole pine and hybrid spruce are common in the higher-elevation ESSFwk1 (Steen and Coupé 1997; B.C. Ministry of Forests 2002). In contrast, the SBPSxc is a relatively low-productivity, dry, cold subzone on the Chilcotin plateau to the west of the Fraser River, where the only recommended regeneration species is lodgepole pine (B.C. Ministry of Forests 2002). The SBPSxc site was classifed as IDFdk4 when EP904.02 was initiated, and as a result, Douglas- fr was tested as a native species for this site. Performance of all species except lodgepole pine was extremely poor at this location; therefore, this discussion focusses primarily on tree responses at the other three sites.

4 .1 Lodgepole Pine, We report frst on growth of the native species in our experiment to provide Douglas-fir, and a basis for evaluating and comparing the performance of introduced species Hybrid Spruce in the following sections. As expected, shade-intolerant lodgepole pine increased in height and diameter considerably more rapidly than more shade-tolerant Douglas-fr and hybrid spruce until at least year 16. Beyond that age, growth rates for Douglas-fr gradually gained on those of lodgepole pine, a phenomenon that has been observed in other Cariboo Region studies (Newsome et al. 2016a). Although average height growth of Douglas-fr was less than that of lodgepole pine at age 22, site index estimates for Douglas-fr were 2–3 m higher than those for lodgepole pine at the ICHwk2 and SBSmw sites. Hybrid spruce grew more slowly than lodgepole pine and Douglas-fr throughout the 22-year period. Slow early growth is typical for standard spruce stock (Coates et al. 1994) and has been observed in other Cariboo Re- gion studies (Newsome et al. 2016a, b). Since western larch, Siberian larch, and ponderosa pine are all shade-intolerant pioneer species that have rapid juvenile growth rates, lodgepole pine provides a relevant baseline comparison to age 22. Over the longer term, growth comparisons between the introduced species and Douglas-fr and hybrid spruce will be of increasing interest. Survival is also an important factor for assessing performance, and ideally, we would compare responses of the introduced species to that of all three native species. Survival outcomes were somewhat confounded at the SBSmw and ESSFwk1 sites, which makes it a less reliable criterion for comparison than growth. At the SBSmw site, there were unexplained early declines in survival of all species, even lodgepole pine, which generally has low rates of early mortality in the SBS zone (e.g., Boateng et al. 2012; Newsome et al. 2016a). Stock

30 for the six species tested at that site came from different nurseries, which suggests that the problem developed after stock arrived at the site. There was little evidence of frost or hare damage in the year of planting at this site, so poor on-site handling or planting techniques may have been responsible. An atypi- cal lodgepole pine survival response also occurred at the ESSFwk1 site, with approximately 40% of seedlings dying within 1 year of planting. Since on-site handling and planting of experimental stock were consistent across species, this suggests that lodgepole pine stock may have been compromised during nursery production or transport. This assumption is supported by reports of low survival (48%) in operational areas of the cutblock that were planted with the same lodgepole pine seedlot.

4 .2 Western Larch Western larch in our study had higher survival and better growth at the ESSF- wk1 site than at the SBSmw or ICHwk2 locations, which we attribute primarily to the ESSFwk1 stock having been grown from a seedlot that was better adapted to moist conditions than was the seedlot used for the other sites. Larch populations that are native to warm, moist climates tend to have the highest growth potential (Rehfeldt and Jaquish 2010); the seedlot used at the ESSFwk1 site was collected at an ICHdw site in the West Kootenay seed planning zone, which is in the Moist Climatic Region of the former Nelson Forest Region (Braumandl and Curran 1992). In contrast, stock for the ICHwk2, SBSmw, and SBPSxc sites was grown from seed collected at an IDF (probably IDFdm1) site in the Thompson Okanagan Dry seed planning zone, which has lower relative growth potential,3 and which may not have been well-suited to the fresh to moist soil conditions of the ICHwk2 and SBSmw. The use of more than one seedlot was unplanned but demonstrates the strong role that genetic suitability can play when a species is extended beyond its range. Almost 80% of western larch planted at our ESSFwk1 site survived to age 22, and at that age, trees were approximately as tall as lodgepole pine (9 m). This survival and growth is surprisingly good considering the relatively short growing season and long snowpack duration in the ESSFwk1 (Steen and Coupé 1997), and that our research site is 25–30 km east of the LW2 seed planning zone. In contrast, western larch at the SBSmw and ICHwk2 sites declined gradually in vigour and survival until only about 40% of the original planted trees were in good or fair condition at age 22. The survivors were approximately 80% as tall as lodgepole pine, and continued to grow slightly more slowly. At all three of these sites, forking was the most common type of damage that affected western larch, although most of it was not serious enough to be considered a growth and yield defect at age 22. It is not clear whether forking was caused by frost or snow damage; western larch is said to have a high tolerance to snow loading because of its open crown and deciduous nature, but it is only moderately frost-tolerant (Klinka et al. 2000; Parent et al. 2008). LePage and McCulloch (2011)4 also documented considerable forking of western larch in some off-site SBS zone plantations that had been established in central and northern British Columbia over the past 35 years; they attributed the damage to frost and snow-related breakage, and suggested that this is a

3 B. Jaquish, B.C. Ministry of Forests, Lands and Natural Resource Operations, Research Branch, Kalamalka Forestry Centre, pers. comm., June 2008. 4 LePage, P. and L. McCulloch. 2011. Assessment of off-site tree plantations in the northwest interior of British Columbia – project summary. Prepared for the Forest Genetics Council of British Columbia. Unpubl. rep. www.fgcouncil.bc.ca/Off-Site_Species_Assessment_Final_Report_Opt.pdf (Accessed Jan. 5, 2016).

31 potentially important growth and yield consideration. Snow breakage is most likely to be an important consideration in areas that receive heavy snows in early spring, after the emergence of western larch foliage. In our experiment, we speculate that western larch performance would have been even better at the ICHwk2 and SBSmw sites than at the ESSFwk1 location if the West Kootenay seedlot had been used throughout. We base this on our understanding that western larch is ecologically better suited to the slightly warmer conditions of the ICH and SBS (Klinka et al. 2000). With the exception of lower elevations in the ESSF in southeast British Columbia (MacKillop and Ehman, in press), western larch has only minor presence in the ESSF within its natural range in southeastern British Columbia; it is, however, common in the ICH zone (Klinka et al. 2000). Rehfeldt and Jaquish’s (2010) modelling suggested that within the Cariboo Region, only 12% of the ESSFwk subzone is suitable for western larch, compared with 75% of the SBSmw and 55% of the ICHwk. Recent survey results from off-site western larch plantations in central and northern British Columbia also indicate that western larch height growth can exceed that of native species on some SBS sites (LePage and McCulloch 20115). Western larch performed very poorly at our SBPSxc site, exhibiting survival and growth rates that were similar to those of Douglas-fr. The few trees of these two species that survived to age 22 were in poor condition and did not exceed 75 cm in height. Newsome et al. (2016a) also found that Douglas-fr could not increase in height at a similarly harsh IDF site on the Chilcotin plateau, apparently because of repeated frost and winter injury. The SBPSxc comprises approximately 1.1 million hectares in the Cariboo Region, and 4% of that area (nearly 50 000 ha) overlaps the LW1 seed planning zone for western larch. It is likely that these overlapping areas are at the periphery of the subzone, where climatic limitations are less severe than at our research site; however, we suggest using caution with regard to planting western larch in the SBPSxc. From a growth and yield perspective, western larch also performed very well at our ESSFwk1 site. Although individual tree volume continued to be signifcantly smaller than that of lodgepole pine at age 22, year 16–22 volume growth of the two species was statistically similar. Gross stand-level western larch and lodgepole pine volume per hectare was also statistically similar at the ESSFwk1 site; however, the relatively small magnitude of the difference (22%) is at least partly due to pine at that site having sustained unusually high planting-season mortality. Estimated site index for western larch at the ESSFwk1 site was more than 1 m higher than that of lodgepole pine, which suggests that it has the higher long-term growth potential, and will do well if it outgrows forking damage. Growth and yield performance of western larch was poorer at the SBSmw and ICHwk2 sites than at the ESSFwk1 location due to lower survival and lesser rates of growth. At the SBSmw installation, larch had only 40% the individual stem volume and 27% the gross stand volume of lodgepole pine. The gap between average individual stem volume of western larch and lodgepole pine was smaller at the ICHwk2 site, but this appeared to be due to poorer lodgepole pine growth rather than better western larch growth. The high survival of lodgepole pine at that site resulted in it having almost three times the stand-level volume of western larch at age 22. Although western larch had, on average, achieved a height of only 7 m at age 22, site index estimates suggest that its growth potential at that

5 Ibid.

32 site was higher even than at the ESSFwk1 site, where the more productive seedlot was used. Western larch site index at the ICHwk2 site was estimated to be approximately 2 m greater than that of lodgepole pine, and second only to that of Douglas-fr. In contrast, western larch site index estimates for the SBSmw site suggest that western larch growth potential was slightly less than that of lodgepole pine and considerably less than that of Douglas-fr. Continued monitoring of this site will be critical for evaluating the rotation-age viability of western larch as a commercial tree species in the Cariboo Region.

4 .3 Siberian Larch The Raivola Siberian larch seedlot used in our study has high growth potential (Viherä-Aarnio and Nikkanen 1995), and between years 21 and 22, it had average leader lengths of more than 50 cm at the ICHwk2 and SBSmw sites. At both these locations, it exhibited better survival and growth than western larch that originated from the Thompson Okanagan Dry seed planning zone. With the exception of western larch at the ESSFwk1 site, Siberian larch also had the second-best height growth rates in the study after lodgepole pine. Site index estimates for Siberian larch indicated that its growth potential was similar to that of lodgepole pine at all research locations; however, estimates may be less reliable than those for other species because we lacked species-specifc site index models. In terms of individual stem volume and stand-level volume, Siberian larch performed as well or better than western larch at the SBSmw and ICHwk2 sites. At the ESSFwk1 installation, where western larch was thriving, Siberian larch had only about three-quarters the individual stem and stand-level volume as that of western larch. The main negative attribute of Siberian larch in our study was related to its form; the year 22 growth and yield assessment indicated that forking and crooking defects were considerably more serious among Siberian larch than western larch. In a Swedish study, snow breakage, forking, and crooked stems were also the most common types of damage that affected Siberian larch (Martinsson 1995). Siberian larch performed poorly but better than western larch at our SBPSxc site. More than one-half of the Siberian larch survived to age 22 and achieved an average height of almost 2 m at that age. This suggests that Siberian larch was gradually growing through the layer of cold air accumulation (Stathers and Steen 1990), which western larch was unable to do. Further, Siberian larch survived winter weather events that killed most ponderosa pine between years 10 and 16 at that site. Siberian larch had poor form at the SBPSxc installation, however, and at age 22, more than 40% had forks or crooks that were serious enough to be noted as growth and yield defects. The damage severity is somewhat surprising, since in its native habitat, Siberian larch reportedly tolerates temperatures as low as –50° C (Larsson-Stern 2003). It prefers moist, deep soil (Larsson-Stern 2003), however, and its vigour and ability to withstand stress may have been reduced by the presence of a root-restricting layer and dry soil conditions at the SBPSxc site, both of which are typical of that biogeoclimatic subzone (Steen and Coupé 1997) and which were not alleviated by the disc trenching that was used at that site.

4 .4 Ponderosa Pine Ponderosa pine performed moderately well at our ICHwk2 and SBSmw sites considering that it was substantially north of its current geographic range and growing at the limits of its edaphic moisture tolerance (Klinka et al. 2000). Its

33 survival was similar at these sites (approximately 60%), but height growth after 22 years was significantly better in the slightly drier climate of the SBSmw than the ICHwk2. At both these sites, ponderosa pine was approximately three-quarters as tall as the 9–10 m tall lodgepole pine at age 22 and had about two-thirds the individual stem volume. The slightly higher survival and slightly better growth of ponderosa pine at the SBSmw location resulted in it achieving about two-thirds the stand-level volume per hectare of lodgepole pine at that site, in comparison with only about 40% as much at the ICHwk2 installation. Site index estimates based on age 22 tree size indicated that ponderosa pine was the least productive of any species at the ICHwk2 site but that it had slightly better long-term potential than western larch or hybrid spruce at the drier SBSmw site. Continued monitoring of these sites will determine the actual growth potential of ponderosa pine at rotation age. In spite of its ability to withstand dry conditions, ponderosa pine had poor survival and growth at the SBPSxc site. In 1987, when EP904.02 was initiated, this site was classified as IDFdk4, and ponderosa pine was thought likely to perform as well as at other IDFdk4 experimental sites (Newsome et al. 2016a). The harsher conditions at the SBPSxc site were obviously beyond its tolerance. Ponderosa pine vigour declined steeply until age 10 at this location, after which there was extensive mortality. Subjective observations suggest that mortality was probably caused by brief periods of warming that induced trees to respire when they were unable to take up water from the frozen soil (winter desiccation) (Krasowski et al. 1993).

4.5 Management Western larch is now an acceptable regeneration species in Cariboo Region Considerations ecosystems that overlap the LW1 and LW2 seed planning zones. Like lodgepole pine, western larch is a shade-intolerant pioneer species that has rapid juvenile growth, but it has, at least within its current range, fewer serious health problems. It is hoped that the availability of western larch as a planting option will reduce the dominance of lodgepole pine as the regeneration species of choice, which will increase diversity and potentially improve forest health at stand and landscape scales. Western larch also has features in common with Douglas-fir as it matures, namely fire resistance and high-quality wood (Parent et al. 2008). Larch has the advantage of becoming increasingly resistant to Armillaria root disease after approximately age 20–25 (Cleary et al. 2008), however, which makes it a potentially good replacement for Doug- las-fir on high-risk sites. Western larch cannot take the place of Douglas-fir in ecosystems where mule deer winter range must be maintained because the deciduous canopy does not intercept snow, and also because fallen Douglas- fir needles constitute an important winter food source for ungulates. Western larch commonly forms mixtures with lodgepole pine and Doug- las-fir throughout its natural range in southeastern British Columbia (Klinka et al. 2000), which suggests that it is suitable for inclusion in SBSmw and ICHwk2 plantations. It also appears in mixtures with Engelmann spruce in the recently defined ESSFwh and ESSFmh subzones of southeastern British Columbia (MacKillop and Ehman, in press), again implying that it can be ad- mixed with spruce in Cariboo Region ESSFwk1 openings that are within the LW2 seed planning zone, particularly on warmer sites. Assisted migration of species beyond their natural range has associated risks that must be weighed against those expected to arise from doing nothing

34 (McLachlan et al. 2005). For example, the assisted migration of potentially invasive species could result in unacceptable ecosystem change, and that risk must be weighed against potential species loss without interference. Western larch is not potentially invasive, however, and risk is viewed primarily from the perspective of possible plantation failure (B.C. Ministry of Forests, Lands and Natural Resource Operations 2014). As a way of minimizing this risk, interim guidelines limit the proportion of planted western larch seedlings within individual management areas to 10% (B.C. Ministry of Forests, Lands and Natural Resource Operations 2014), and it is recommended that the species constitute a maximum of 50% of the stocking on individual sites.6 Experimental Project 904.02 also suggests that Siberian larch can success- fully be grown on Cariboo Region SBSmw, ICHwk2, and ESSFwk1 sites. It will be interesting to monitor growth and yield performance of this species over the longer term. From a practical perspective, we think the large amount of research that would be necessary to support operational introduction of this species is unwarranted considering the likelihood of higher success with assisted western larch migration in these ecosystems. At the SBPSxc site, although Siberian larch sustained severe forking, the fact that more than one-half of the original planted trees survived and were able to grow through the layer of cold air accumulation warrants consideration. Lodgepole pine is currently the only species that is recommended for planting on zonal sites in the SBPSxc (B.C. Ministry of Forests 2002). If Siberian larch eventually outgrows the forking damage, it could be a potential alternative. Should there be further interest in Siberian larch as a planting species in British Columbia, considerable new research has been conducted in Scandinavia that could help guide operational testing (e.g., Larsson-Stern 2003). Ponderosa pine survived and grew moderately well at our ICHwk2 and SBSmw sites, and proved to be second only to lodgepole pine in terms of its ability to gain volume at an early age. From a forest health perspective, there may be little beneft to introducing ponderosa pine into the species mix in moist Cariboo Region ecosystems because it is subject to most of the same damaging agents as lodgepole pine, including mountain pine beetle, hard pine stem rusts, and pine needle cast (Henigman et al. 2001). Furthermore, it is unlikely to be economically valuable, especially in the ICHwk2, where it had lower site index than any other species. At age 22, ponderosa pine was subjectively described as having undesirable form at that site—trees had wide crown and large branches, traits that are undesirable from the perspective of wood quality and economic value (Groot and Schneider 2011). The performance of ponderosa pine should be monitored until maturity at the EP904.02 sites, especially in the SBSmw, where our results suggest it has moderate growth potential. Ponderosa pine’s range is predicted to expand by approximately 300% by 2055 and approximately 600% by 2085 (Hamann and Wang 2006), and the drought and fre tolerance characteristics of this species (Klinka et al. 2000) may be benefcial attributes.

6 J. Snetsinger, Chief Forester, British Columbia (memorandum dated Dec. 15, 2010).

35 5 Conclusion

The need to proactively manage for conifer tree species diversity and forest resilience in south−central British Columbia became obvious in the wake of the mountain pine beetle epidemic and the mounting evidence of forest health issues regarding lodgepole pine (e.g., Woods et al. 2005; Heineman et al. 2010). The inclusion of western larch in climatically suitable areas is intended to mitigate anticipated negative effects of climate change on forest health,7 issues that are particularly important for productive ecosystems in the ICHwk2 and SBSmw that naturally support diverse tree species mixtures. Our results to age 22 for the two seedlots examined in this study support the inclusion of western larch that originates from climatically similar ecosystems in reforestation programs in the SBSmw, ICHwk2, and ESSFwk1. Our results do not support inclusion of western larch in reforestation programs for the SBPSxc, where the harsh climate appears to preclude use of any species except lodgepole pine. Experimental Project 904.02 provides an opportunity to monitor western larch responses in the ICHwk2, SBSmw, and ESSFwk1 until tree maturity. The interim guidance regarding western larch was developed on the basis of climate projections to 2030, which is now less than 15 years away; data from older stands can potentially contribute to timber supply modelling and help identify forest health concerns that may not be evident at age 22. Ongoing growth and yield monitoring will also facilitate longer-term comparison of western larch with Douglas-fr and hybrid spruce, which although highly productive, typically exhibit slower early growth than shade-intolerant species. TheLW 1 and LW2 distributions were developed based on modelling outcomes that have a margin of error (Rehfeldt and Jaquish 2010); we therefore recom- mend that Cariboo Region plantations where western larch is introduced should be carefully monitored for health and growth well beyond the juvenile stage. Furthermore, the LW1 and LW2 boundaries were defned based on climate-change projections, and do not match boundaries currently defned by biogeoclimatic classifcation. Biogeoclimatic classifcation is the basis for forest management in British Columbia, and to facilitate operational use of western larch as a regeneration species, we suggest developing stocking guidelines by biogeoclimatic unit as a next phase of this project.

7 J. Snetsinger, Chief Forester, British Columbia (memorandum dated Dec. 15, 2010).

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40 – – – – Seedlot Seedlot 855–1555 780–1280 510–1010 806–1506 753–1153 814–1214 775–1475 775–1475 775–1475 746–1546 range (m) range 1080–1580 1080–1580 1080–1580 1250–1650 1200–1600 1140–1740 1140–1740 elevational elevational 850 850 850 850 850 850 1140 1340 1250 1340 1250 1140 1250 1140 1340 1140 1250 1140 1250 1140 1340 (m) Site elevation elevation – – – – Seedlot Seedlot 117°05'–122°05' 117°05'–122°05' 114°10'–119°10' 117°05'–122°05' 119°37'–124°37' 120°07'–125°07' 120°23'–125°23' 119°07'–124°07' 120°35'–125°35' 119°27'–124°27' 119°14'–124°14' 114°00'–118°50' 114°00'–118°50' 114°00'–118°50' 118°45'–125°45' 119°56'–126°56' 119°49'–126°49' latitudinal range latitudinal Site longitude 120°57.35' 122°14.65' 121°50.54' 122°50.79' 122°50.79' 120°57.35' 122°14.65' 122°50.79' 120°57.35' 122°14.65' 121°50.54' 122°14.65' 121°50.54' 120°57.35' 122°50.79' 120°57.35' 122°14.65' 122°50.79' 120°57.35' 122°14.65' 121°50.54' – – – – range Seedlot Seedlot latitudinal 48°04'–51°04' 48°04'–51°04' 48°06'–51°06' 48°04'–51°04' 51°25'–54°25' 51°41'–54°41' 50°58'–53°58' 51°07'–54°07' 51°55'–54°55' 52°08'–55°08' 51°16'–54°16' 48°37'–51°37' 48°37'–51°37' 48°37'–51°37' 51°18'–54°18' 52°00'–55°00' 51°54'–54°54' 52°22.81' 52°57.68' 53°18.21' 52°00.42' 52°00.42' 52°22.81' 52°57.68' 52°00.42' 52°22.81' 52°57.68' 53°18.21' 52°57.68' 53°18.21' 52°22.81' 52°00.42' 52°22.81' 52°57.68' 52°00.42' 52°22.81' 52°57.68' 53°18.21' Site latitudeSite Vernon Vernon Vernon Vernon Nursery IFS Surrey Pelton Silv. World Surrey Reid Collins Ruff's IFS Telkwa IFS Koksilah Skimikin Skimikin Skimikin Surrey Hygro Ruff's c – – – – 3395 3395 5235 3395 2419 8476 2373 3786 2115 8456 0233 0233 0233 2866 4305 4050 1043 Seedlot 313 1+0 313 1+0 313 1+0 313 1+0 211 1+0 211 1+0 313 1+0 313 1+0 313 1+0 313 1+0 211 1+0 211 1+0 313 1+0 313 1+0 313 1+0 313 1+0 313 1+0 313 1+0 313 1+0 313 1+0 313 1+0 Stocktype psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb psb a SBSmw ESSFwk1 ICHwk2 SBPSxc SBSmw SBPSxc SBPSxc SBSmw SBPSxc ESSFwk1 ICHwk2 ICHwk2 SBSmw ESSFwk1 ICHwk2 ESSFwk1 SBSmw SBPSxc SBSmw ICHwk2 ICHwk2 Site Stocktype, seedlot, and nursery information (grey highlighted cells indicate where the site is outside recommended range for seedlot) b origin latitude latitude origin ussr Karelia; southern Raivola, is Provenance Finland. in Imatra, seed orchard seed the Enso-Gutzeit from second-generation from grown was stock larch Siberian would be a suitable choice for the study site. the study for choice be a suitable would gelmann Spruce – Subalpine Fir zone; SBPSxc is the very dry, cold Sub-Boreal − Pine Spruce zone. Spruce − Pine Sub-Boreal cold the very is dry, SBPSxc zone; Fir – Subalpine Spruce gelmann 10.0 g/1000 seeds. of a weight with 99% seed 48% was on purity, 1985 in February conducted test A germination m elevation. 70 28°48' E at N and 61°12' ICHwk2 is the Quesnel variant of the wet, cool Interior Cedar – Hemlock zone; SBSmw is the moist warm Sub-Boreal Spruce zone; ESSFwk1 is the Cariboo variant of the wet, cool En - the wet, of the Cariboo is ESSFwk1 variant zone; Spruce Sub-Boreal warm the moist is SBSmw zone; Cedar – Hemlock cool Interior the wet, of variant the Quesnel is ICHwk2 The seedlot number was incorrectly recorded as 1034, which is not a lodgepole pine seedlot. We have made the assumption that the correct number is 1043, which is an SBS seedlot that SBS seedlot an that is which is 1043, number correct the that assumption made the have We pine seedlot. a lodgepole not is as 1034, which recorded incorrectly was number The seedlot Siberian larch Western larch Western Douglas- f r Lodgepole pine Ponderosa pine Ponderosa spruce Hybrid Species APPENDIX 1 a b c

41 APPENDIX 2 Assessment codes for vigour, overtopping, damage, and damage cause (used by the Cariboo Region’s Research Section)

A. Criteria Used 1989–2000

Code Overall Seedling Conditions 1 Good The seedling shows no signs of stress and has a vigorous growth rate and a generally healthy appearance. 2 Fair The seedling is under some form of stress, may have minor defects, and has a moderate growth rate. 3 Poor The seedling is under severe stress, may have major defects, and the growth rate is poor. 4 Moribund The seedling is almost dead. 5 Dead 6 Missing 7 Destructively Sampled

Vegetation Cover Codes O Overtopped The leader of the crop tree is at present overtopped by surrounding vegetation; crop tree available sunlight is greatly reduced. T Threatened The leader of the crop tree is at or near the same height of the surrounding vegetation but is likely to be overtopped within two growing seasons. F Free of Vegetation1 The leader of the crop tree is well above the surrounding vegetation and is not likely to become threatened. 1 The term was changed from “free-to-grow” to avoid confusion with legislated free-growing status.

Seedling Damage Codes Stem condition code Foliage condition code Damage condition code H – No visible effect (healthy) H – No visible effect (healthy) A – None P – Bark peeled or abraded Y – Chlorotic (yellow) H – Herbicide B – Stem bent M – Mottled M – Mechanical equipment S – Stem smashed, crushed, trampled N – Necrotic T – Hand tools C – Stem cut, clipped, broken A – Needles absent, defoliated S – Falling slash (human caused) D – Tree dead, dying B – Browsed X – Falling or sliding debris M – Tree missing D – Dead buds on lateral branches E – Climate — frost F – Stem forked G – Gall aphid N – Snow press G – Gall rust Ø – Other symptoms (specify) V – Vegetation press Ø – Other symptoms (specify) W – Climate drought Leader shoot condition code R – Rodents, small animals H – No visible effect (healthy) B – Big game C – Curled L – Livestock F – Forked F – Fire B – Browsed I – Insects T – Dead terminal bud D – Disease S – Snapped, broken Z – Destructively sampled A – Absent, missing G – Winter — damage P – Pissodes P – Whipping damage Ø – Other symptoms (specify) Ø – Other (specify) N – No or abnormal flush U – Unknown

42 B. Criteria Used 2001–2012

Code Tree/Seedling Vigour 1 Good The seedling shows no signs of stress and has a vigorous growth rate and a generally healthy appearance. 2 Fair The seedling is under some form of stress, may have minor defects, and has a moderate growth rate. 3 Poor The seedling is under severe stress, may have major defects, and the growth rate is poor. 4 Moribund The seedling is almost dead. 5 Dead 6 Missing 7 Destructively Sampled

Seedling Vegetation Cover Codes O Overtopped The leader of the crop tree is at present overtopped by surrounding vegetation; crop tree available sunlight is greatly reduced. T Threatened The leader of the crop tree is at or near the same height of the surrounding vegetation, and/or is likely to be overtopped within two growing seasons. F Free of Vegetation1 The leader of the crop tree is well above the surrounding vegetation and is not likely to become threatened. 1 The term was changed from “free-to-grow” to avoid confusion with legislated free-growing status.

Tree /Seedling Damage Codes (fd, ld, sd) Foliage/branch damage code Leader damage code Stem damage code Healthy H Healthy H Healthy H Mottled M Curled C Stem bent or leaning B Necrotic N Dead terminal bud on leader T Stem smashed, crushed, trampled S Needles absent, defoliated A Dead previous year terminal bud NL Stem cut, clipped, broken C — new leader(s) established Browsed B No elongation of terminal N Stem forked F Dead buds on lateral branches D Browsed B Bark removed or abraded (> 25%) P Chlorotic Y Absent or broken S Gall G Gall on foliage or branch tip GA Insect entry holes P Spindly SP Gall on wood of branch GR Dead top DT Main stem is dead or dying D Reduced needle size Z Forked (> 1 equally dominant) F Crook K Broom R Needles absent on leader AN Stem canker from disease or insect SC Other symptoms O Other symptoms O Other symptoms O

43 Damage Cause Codes (fc, lc, sc) General (use specific cause if known)a Specific None A Herbicide H Pine needle cast (Lophodermella concolor) DFL Mechanical equipment or hand tools M Western gall rust (Endocronartium harknessii) DSG Falling or sliding debris or slash X Gall aphid (Adelges cooleyi) IAG Frost FR 2-cycle budworm (Choristoneura biennis) IDB Snow press SP Western spruce budworm (Christoneura occidentalis) IDW Vegetation V Spruce weevil (Pissodies strobi) IWS Drought DR Pine terminal weevil (Pissodes terminalis) IWP Rodents, small animals R Northern pitch twig moth (Petrova albicapitana) IMP Big game B Whipping damage WH Livestock L Mountain pine beetle IBM Fire F Elytroderma DFE Insects: Specify if known I Herbaceous vegetation competition VH Disease: Specify if known D Shrub vegetation competition VS Destructively sampled Z Broadleaf tree vegetation competition VB Winter damage WD Conifer tree competition VC Wind (i.e., windthrow) W Other (specify) O Unknown U Tag TAG a For codes, see B.C. Ministry of Sustainable Resource Management (2003); for descriptions, see Henigman et al. (2001).

44 093