Sample collection
We collected branch samples from two Department of Energy (DOE) common gardens in Oregon, USA in January of 2017. The gardens are located near Clatskanie, Oregon (46.12˚N, 123.27˚W; MAT = 10.4oC, MAP = 1,545 mm) and Corvallis, Oregon (44.56˚N, 123.26˚W; MAT = 11.2oC, MAP = 1,030 mm) respectively, which represent contrasting environments with similar daylength patterns (Figure 2A). Each garden contains the same 1,060 unique genotypes from 19 populations, which were replicated clonally three times each and planted out in 2009. The collection of each accession is described in Slavov et al. (2012). However, we only sampled genotypes from 17 of the populations, as some populations had high mortality, and from the 917 of 1,060 which have full genomic information available(Evans et al., 2014) (Figure 1). In Corvallis, all three replicates were coppiced (aboveground biomass harvested) in the winter of 2013-2014, while only one replicate was coppiced in Clatskanie during the same period (Figure 1). Thus, we only sampled branches from coppiced replicates for this study. Non-coppiced trees in Clatskanie had an average diameter at breast height (DBH) in 2016 of 155.2 ± 46.9 mm, while coppiced trees averaged 84.0 ± 28.0 mm. DBH in Corvallis across all coppiced replicates in 2016 was 44.4 ± 14.9 mm.
We collected all samples between January 6th and January 11th 2017, between 7 A.M. and 4 P.M. using pruning shears for branch sampling. We took all branch samples as 2cm segments from the previous growing season’s growth segment (2015) of coppiced replicates as it was accessible across all individuals. All samples were kept on dry ice during field collection, then shipped overnight to Cambridge, MA and stored at -80OC. In total, we collected and processed 616 branch samples (Figure 1). We collected additional stem and root tissue during this time period and included aspects of this work in the discussion for comparison (Blumstein et al., 2020)(Table S1).