2.5.1 Bivariate growth pattern analyses
Our primary objective was to determine how variation in tree growth rates and climate sensitivity changes with altitude and with the species composition of neighboring trees. We began our analysis by conducting correlation tests to estimate the responsiveness of tree-level growth synchronies and log-transformed BAI for both Picea andFagus to elevation and neighborhood species composition. Mean BAIs were estimated over a recent time window that is common to all trees (c. 1980-2010) to minimize the potential impact of unobserved changes in local forest structure on individual tree growth (Buechling et al. 2017). To understand the importance of competition, and to disentangle the importance of intraspecific vs. interspecific competition, we narrowed the scope of this analysis to the altitudinal range where Picea and Fagus overlap (900m to 1300m). We then again conducted correlation tests to quantify relationships between species diversity (using Shannon’s diversity index; H = -sum[ pi * log(pi) ] ), log(BAI) and synchrony.