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.