Supplement 1. Latitudinal difference distributions, associated rates of temperature change, and trait values for each species in the contemporary data set.

File List LDD_for_Northern_Edge.csv (MD5: 8963d2b01800440c827e56c38d3d80d4) LDD_for_Southern_Edge.csv (MD5: c6cf2c82cb42d15b106f12a58ebdd501) Description The LDD_for_Northern_Edge.csv and LDD_for_Southern_Edge.csv files are comma delimited files. They contain species level data on latitudinal difference distributions at the northern and southern range edges, respectively, along with associated climate velocities. Columns 1. FIA species code = USFS numerical code for each tree species 2. Common name = species common name, following USFS conventions 3. Species = latin binomial for each tree species 4. Family = Botanical family of each tree species 5. Mycorrhizal Guild = type of mycorrhizal association (AM = arbuscular mycorrhizal, EM = ectomycorrhizal, Dual = dually colonized by both AM and EM fungi) 6. Shade Tolerance = numerical rank denoting qualitative shade tolerance scores (1 = Very intolerant, 2 = Intolerant, 3 = Intermediate, 4 = Tolerance, 5 = Very Tolerant) 7. ln(Seed Size) = Species mean seed mass, natural log transformed 8. Climate Velocity = rate of temperature change at the northern (or southern) range boundary over the last century 9. LDD = Species mean Latitudinal difference distribution using the methods described in main text (based on median latitude of observations within 1° latitude of most extreme tree observation). 10. LDD 95% CI = 95% confidence intervals of species mean LDD across longitudinal bands 11. LDD (using minimum observation) = Species mean Latitudinal difference distribution using only the most extreme observations of trees and seedlings 12. LDD 95% CI = 95% confidence intervals of species mean LDD using minimum observations across longitudinal bands 13. LDD (using minimal 5% of observations) = Species mean Latitudinal difference distribution using the observations at the 5% (southern edge) or 95% (northern edge) of observations. 14. LDD 95% CI = 95% confidence intervals of species mean LDD using 5 percentile observations across longitudinal bands 15. BV-CV = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 9. 16. BV-CV (using minimal observation) = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 10. 17. BV-CV (using minimal 5% of observations) = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 11.