Is there a tree economics spectrum of decomposability?

Abstract

The plant economics spectrum (PES) integrates trade-offs and coordination in resource traits among species within and between organs, and affects ecosystem processes such as litter decomposition. This PES is currently based on trait variation among a wide range of plant types and growth forms. Here we ask whether the PES also features within the same growth form, i.e. within and between organs among temperate tree species. If so, is there a tree economics spectrum (TES) of decomposability driving the decomposition rates across the coarse branches, twigs and leaves of different species? And how robust would this TES of decomposability be to different environmental conditions? To investigate these questions, we conducted a “common garden decomposition experiment” with ten temperate tree species in two contrasting forest environments in the Netherlands for 47 months. We evaluated the effects of functional traits of leaves, twigs, branch wood and branch bark on the decomposition rates of those organs. We measured the same resource traits for all those organs of the ten tree species and assessed whether there was a multivariate axis of functional traits explaining decomposition rates in both environments. We report three key findings. First, tree organ specific economics spectra were significantly correlated with each other for the studied tree species. Second, tree organs differ significantly in decomposition rates, i.e. leaves were consistently more decomposable than twigs and twigs more than coarse branches. Third, we found some evidence of a TES with important afterlife effects driving coordinated decomposability of twigs and leaves but not of coarse branches across the tree species, and the effects of this TES on decomposition rates strongly depended on local forest environment. The consistent contrasting decomposability between tree organs across species confirms an important role of plant litter inputs of different organs in forest biogeochemistry and carbon storage. There is also substantial coordination of interspecific trait variation between the finer tree organs. Knowledge about relationships of the TES and decomposability taking interactions with environmental variation into account can help for predicting whole-tree carbon and nutrient turnover as dependent on forest and soil type, even within the same climate zone.