## Supplement 1. Locations of field plots, plot-scale foliar chemical and morphological traits, results of leave-site-out and leave-year-out model cross-validations, and PLSR model coefficients.

## File List

Plot_locations_foliar_traits.csv (MD5: 029b7ae2c45b10eadb5847e8a3871dc8)

per_site_and_year_Crossvalidations.csv (MD5: 149187c633f7dd62ed27b6ff5754f967)

PLS_coefficients_Mode_A_del15N.csv (MD5: 2ffb9111ceb8fd7920f6da687419349a)

PLS_coefficients_Mode_A_M_area.csv (MD5: f5ae47c67b28a520057b463a9f7c9b6b)

PLS_coefficients_Mode_A_pct_ADF.csv (MD5: 0f9326724c54568a894e8fb6019584e2)

PLS_coefficients_Mode_A_pct_ADL.csv (MD5: d526a9843da4c29a20b56f3ac21fce95)

PLS_coefficients_Mode_A_pct_C.csv (MD5: 72a41e0a101b92221995ec4328055257)

PLS_coefficients_Mode_A_pct_Cellulose.csv (MD5: d0a6f931f835023c204fd774e25dad6b)

PLS_coefficients_Mode_A_pct_N.csv (MD5: c3bb8a7499b0889cce803185c3e5771e)

PLS_coefficients_Mode_B_del15N.csv (MD5: 028ed350afbb2dc8fba08b51e5919ac5)

PLS_coefficients_Mode_B_M_area.csv (MD5: 5afa82d3e74680a3de9d545d29a6d6a5)

PLS_coefficients_Mode_B_pct_ADF.csv (MD5: c0e67fdef81d55733ce5517d0c01e103)

PLS_coefficients_Mode_B_pct_ADL.csv (MD5: cece7b51cd41edd4daf5fc5ace3e891e)

PLS_coefficients_Mode_B_pct_C.csv (MD5: 0cd7afa80949a1c5b101b6abb08fb910)

PLS_coefficients_Mode_B_pct_Cellulose.csv (MD5: 3ce2e034ee5dd3f4040d10665398bec5)

PLS_coefficients_Mode_B_pct_N.csv (MD5: a2433d479202b1d6318b15456139f007)

PLS_coefficients_Mode_C_del15N.csv (MD5: a40c8c1e5d6e74693c3c96170bb66470)

PLS_coefficients_Mode_C_M_area.csv (MD5: 83fb7c81e4e54e5cce13fe1ab64c97f2)

PLS_coefficients_Mode_C_pct_ADF.csv (MD5: 919fb19a5668c170ba34c6ab16821442)

PLS_coefficients_Mode_C_pct_ADL.csv (MD5: 543d34f7126016c4c91b8c17ce5c930e)

PLS_coefficients_Mode_C_pct_C.csv (MD5: 977ff98c013cc60871c559952d700b30)

PLS_coefficients_Mode_C_pct_Cellulose.csv (MD5: 3ce2e034ee5dd3f4040d10665398bec5)

PLS_coefficients_Mode_C_pct_N.csv (MD5: 530d8d631fc128b485097306816b4f0e)

PLS_coefficients_Mode_D_del15N.csv (MD5: d15ae6acc62cd48a86561393086149cb)

PLS_coefficients_Mode_D_M_area.csv (MD5: 63b2d2c9d5993b14e5f8d56f99c67c89)

PLS_coefficients_Mode_D_pct_ADF.csv (MD5: 1722fb9dfc76be5d16d514e0c0ce37f1)

PLS_coefficients_Mode_D_pct_ADL.csv (MD5: 9452b93bbd8996320799583526f2cac5)

PLS_coefficients_Mode_D_pct_C.csv (MD5: 7aba2ab18097447adbec2d1593717a42)

PLS_coefficients_Mode_D_pct_Cellulose.csv (MD5: 59c44ea1ddfedef39968b98b1297c489)

PLS_coefficients_Mode_D_pct_N.csv (MD5: af16ca0e230b3fd91b3588ac7cc15fc8)

## Description

Data stored in CSV files (comma delimited text files with header):

** **“Plot_locations_foliar_traits.csv”

Plot: Plot code (AK - Adirondacks NY, BH - Baraboo Hills WI, BI - Blackhawk Island WI, DC - Madison WI, GR - Green Ridge State Forest MD, IDS - Green Ridge State Forest MD, KM - Kettle Moraine State Forest WI, MN - Minnesota Arrowhead MN, NC - Chequamegon-Nicolet State Forest WI, OF - Ottawa National Forest MI, PB - Pine Barrens WI, PM - Porcupine Mountains WI, SF - Sylvania National Forest MI, SR - Savage River State Forest MD), Year: year of sampling, Latitude: geographic Y coordinates (WGS84 ellipsoid), Longitude: geographic X coordinates (WGS84 ellipsoid), spp1: Code, dominant species (see Table A2, Appendix A), rba1: relative basal area of spp1 (fraction), spp2: Code, co-dominant species (see Table A2, appendix A), rba2: relative basal area of spp2 (fraction), CAR: Carbon (mean of % by weight), CAR_sd: Carbon (standard deviation of % by weight), CEL: Cellulose (mean of % by weight), CEL_sd: Cellulose (standard deviation of % by weight), ADF: Acid detergent fiber (mean of % by weight), ADF_sd: Acid detergent fiber (standard deviation of % by weight), ADL: Acid detergent lignin (mean of % by weight), ADL_sd: Acid detergent lignin (standard deviation of % by weight), LMA: Leaf mass per area (mean g/m²), LMA_sd: Leaf mass per area (standard deviation g/m²), NIT: Nitrogen (mean of % by weight), NIT_sd: Nitrogen (standard deviation of % by weight), N15: δ^{15}N (mean of ‰ measured), N15_sd: δ^{15}N (mean of ‰ measured).

“per_site_and_year_Crossvalidations.csv”

Results of leave-site-out and leave-year-out cross-validations for partial least squares models presented in manuscript. Rows are indexed by either year or site (see above for site codes). For each trait (Nitrogen, del15N, Marea, Cellulose, Carbon, ADL and ADF) columns indicate: RMSE cal.: Root mean squared error, calibration; RMSE val.: Root mean squared error, validation; % in Pred. Int.: Percent observations within prediction intervals; % of range: validation RMSE as percent of range of observations; N cal.: Number of calibration samples; N val.: Number of validation samples.

All files in supplement 2 (e.g., ”PLS_coefficients_Mode_A_del15N.csv”) are coefficients obtained from 500 randomized replicates of PLSR models described in the manuscript. The “Mode” (i.e., “**Mode A”** in example above) indicates models built using canopy traits aggregated using canopy weighting schemes described in Table A3, Appendix A. All files are suffixed with the respective response variables (del15N: δ^{15}N [‰], M_area: Marea [g/m²], pct_ADF: ADF [%], pct_ADL: ADL [%], pct_C [%], pct_Cellulose: Cellulose [%], pct_N: Nitrogen [%]). Rows correspond to model replicates (indexed by column “Model”), columns correspond with PLSR model coefficients at nominal wavelengths (i.e., column WVL_453 = PLSR model coefficient for wavelength 453nm.) Columns filled with zeros indicate noise-contaminated (< 414 nm and > 2408 nm) or water absorption bands. Column “Intercept” is the PLSR model constant term.