Environmental gradients modify biotic interactions among tree species in temperate rain forest

Abstract

The realised niche is jointly shaped by both abiotic and biotic processes. Moreover, the strength and direction of biotic interactions may vary across abiotic conditions and generate non-additivities that, if ignored, could lead to inaccurate predictions of species responses to changes in environment and composition. We tested this idea by analysing nationwide forest inventory data that span broad environmental gradients throughout New Zealand. The use of Bayesian shrinkage priors enabled our conclusion that the most complex model—featuring biotic interactions that changed with vapour pressure deficit and higher-order interactions with intermediary species—had the highest predictive accuracy of tree diameter growth. That is, pairwise competition became pairwise facilitation, or vice versa, depending on atmospheric moisture and/or the density of a third species. Our study highlights the importance of the interplay between abiotic and biotic processes when predicting how biotic interactions may structure communities under global change.