Online Appendix Figure S1. Gain, persistence, and loss in potential distribution of western redcedar under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset), based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 1 Figure S2. Gain, persistence, and loss in potential distribution of Sitka spruce under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset) based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 2 Figure S3. Gain, persistence, and loss in potential distribution of western hemlock under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset) based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 3 Figure S4. Gain, persistence, and loss in potential distribution of Pacific silver fir under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset) based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 4 Figure S5. Gain, persistence, and loss in potential distribution of grand fir under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset), based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 5 Figure S6. Gain, persistence, and loss in potential distribution of Alaska yellow-cedar under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset) based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 6 Figure S7. Gain, persistence, and loss in potential distribution of mountain hemlock under the emission scenario A2A for two future time periods (2050s, 2080s) compared to baseline extent (inset) based on degree of agreement among three GCMs (CSIRO, CCCMA, HADCM3). 7 TABLE S1. Expected and modeled distributions of Pacific coastal focal rainforest species based on species experts and the literature. Species Range Habitat Climate Expected Modeled preference envelope shift shift Western Along coast 0-1500m Wet Retraction of High redcedar from Alaska elevation; climates riparian persistence to California, Found on west of the populations throughout also inland various Cascades, as runoff BC and to Alberta, substrates, especially declines and coastal AK. Idaho, and commonly on in BC and fires Expansion to Montana. moist sites, in the Olympic intensify. higher mixed Peninsula. Southern elevations coniferous Dry interior contraction and latitudes. forests. climates of coastal Contraction restricted to range. in SE riparian portions of habitats the range. west of the Rocky Mountain divide. Sitka spruce From Kodiak Usually found Encompasss Retraction of High levels Island south growing on wide range range, of to N. CA. well-drained of precip especially persistence 8 Generally acidic soils. and south of BC, throughout within 20km Tolerant of temperature localized BC and AK of coast or salt spray.2 2. Inability changes in with some with the fog to tolerate response to expansion to belt south of moisture changes in higher B.C. Up to stress disturbance elevations 200km from during regimes. and latitudes. the sea in growing Southern B.C. and season. range AK.1 contraction along CA and OR coast, as well as S. Cascades. Western Alberta and Coastal to Shade Expansion Southern hemlock BC, Canada, mid-montane tolerant. along parts of Alaska, forests. Some elevational Coast Range Washington, Dominant or evidence gradients experience Idaho, found with that they especially greatest loss. Montana, Sitka spruce grew well at along N. Higher Oregon, and in coastal higher coastline, amounts of California forests, elevations and through persistence Douglas-fir in when the Prince in BC and 9 Cascades3 and climate was William Cascades. with western warmer and Sound. Most redcedar. drier.2 opportunity for expansion to higher elevations in BC. Pacific silver Western BC, Deep well- Maritime Loss of Heavy range fir Canada; SE drained soils climate with winter contraction Alaska, W in cool, moist significant snowpack throughout Washington coastal winter should result coastal and and Oregon, forests, snowpack.4 in retraction southern NW descending to Intolerant of of range in portions of California sea level fire. low the range. northward elevation Northward from habitats expansion Vancouver along and Island. From northern expansion to 1000 m to coast.5 In its higher treeline in southern elevations in Oregon and range it BC. further south. would be Typically expected to 10 higher and increase its wetter habitat elevational than grand fir range with and western other redcedar. subalpine Highly shade species. tolerant. Grand fir BC, Canada, Moist sites Areas Likely to Substantial Washington, from 0- where continue to loss of Idaho, 1500m; summer expand as climatic Montana, Riparian drought and fire regimes niche Oregon, and settings along fire are change in throughout California streams and common interior southern rivers in OR west of the regions. portions of and WA. Cascade the range, Above 1000m Crest; throughout in CA2. relatively Cascades Sensitive to moist and Coast changes in habitats in range. fire regimes. interior Extensive regions. potential expansion northward. 11 Alaska West coast, Wet sites7, Limited to Retraction of Coastal and Yellow- from the close to tree wet soils coastal southern cedar Kenai line in south, and high populations; portions of peninsula to to sea level in elevations, restriction to range the Klamath north. Often especially montane contracts. Mountains of in high in the south, habitats due Distribution Northern montane and but also at to snow pack becomes California6 subalpine low requirements patchy forests of the elevations throughout Cascades. in the north. range. Little Vulnerable expansion. to fine-root freezing. Mountain BC, Canada, Found at Relatively Some Coastal and hemlock Alaska, increasing coastal, western southern Washington, elevations with high expansion, portions of Idaho, from AK to snowfall or but mostly range Montana, CA.2 Upper rainfall. localized contracts. Oregon, portion of Mean expansion in CA California, subalpine annual temp elevation populations and Nevada forest to of 3-4° C. upward and become treeline. Cannot loss of lower disjunct. Sometimes tolerate elevation Some grows as frozen soils. populations. expansion 12 krummholz. east (to higher elevations) and north. Coast SW OR and Below 300m Foggy Retraction of Contraction redwood NW CA but coastlines1 southern throughout within 60km occasionally range due to most of the of the coast to 1000m. changes in range. Small Alluvial soils. fog belt and patches of Pure stands or some persistence with Douglas- potential possible. fir or Port expansion Little Orford cedar northward. expansion (Chamaecypa expected. ris Extirpation lawsoniana) 1 throughout range possible. 1 Thompson, R. S., Anderson, K. H., Bartlein, P. J., 1999. Atlas of Relations Between Climatic Parameters and Distributions of Important Trees and Shrubs in North America. USGS Professional Paper 1650 A&B. http://greenwood.cr.usgs.gov/pub/ppapers/p1650- a/pages/conifers.html (accessed 27 June 2014). 2 The gymnosperm Database, Edited by Earle, C. J. http://www.conifers.org (accessed 27 June 2014). 13 3 Franklin, J. F. and Dyrness., C.T., 1988. Natural Vegetation of Oregon and Washington. Corvallis, OR: Oregon State University Press. 4 Pojar, J., Mackinnon, A., 1994. Plants of the Pacific Northwest Coast. Vancouver, BC: Lone Pine Publishing. http:// www.lonepinepublishing.com/cat/9781551055305 (accessed 27 June 2014) 5 Burns, R.M., Honkala, B.H., 1990. Silvics of North America, Vol. 1, Conifers. Washington DC: U.S.D.A. Forest Service Agriculture Handbook 654. http://www.na.fs.fed.us/pubs/silvics_manual/table_of_contents.shtm (accessed 27 June 2014) 6 USGS 1999. Digital representation of "Atlas of United States Trees" by Little, E. L. http://geo-nsdi.er.usgs.gov/metadata/professional-paper/1650/metadata.faq.html (accessed 27 June 2014). 7 Peattie, D. C., 1950. A Natural History of Western Trees. New York: Bonanza. 14 TABLE S2. Shown Kappa values serve as measurement of agreement between baseline potential species distributions and future potential distributions for all modeled species. Lower values indicate less accordance. Species 2050s 2080s CSIRO CCCMA HADCM3 CSIRO CCCMA HADCM3 Western redcedar 0.708 0.778 0.673 0.567 0.671 0.556 Sitka spruce 0.747 0.852 0.834 0.631 0.796 0.799 Western hemlock 0.806 0.863 0.803 0.668 0.777 0.71 Pacific silver fir 0.503 0.713 0.549 0.334 0.565 0.468 Grand fir 0.676 0.716 0.47 0.373 0.525 0.265 Alaska yellow-cedar 0.8 0.854 0.814 0.56 0.738 0.692 Mountain hemlock 0.696 0.78 0.743 0.541 0.638 0.619 Coast redwood 0.644 0.397 0.648 0.626 0.083 0.458 mean of scenario 0.698 0.744 0.692 0.538 0.599 0.571 mean of period 0.711 0.569 15 TABLE S3. AUC values for focal rainforest species based on training and test data averaged across 25 Maxent model runs. Thresholds used for converting probability surfaces into presence/absence data are shown including values for sensitivity and specificity. Species AUC[training] AUC[test] threshold sensitivity specificity Western redcedar 0.85 0.85 0.35 0.88 0.95 Sitka spruce 0.90 0.90 0.20 0.88 0.93 Western hemlock 0.82 0.82 0.30 0.92 0.89 Pacific silver fir 0.89 0.88 0.43 0.88 0.96 Grand fir 0.88 0.88 0.28 0.96 0.93 Alaska yellow-cedar 0.92 0.92 0.22 0.92 0.90 Mountain hemlock 0.90 0.90 0.21 0.94 0.90 Coast redwood 0.94 0.93 0.20 0.95 0.83 16 TABLE S4. Overview of training gain values that were used as thresholds for WorldClim predictor selection for final climate envelope models, based on preliminary model runs.