Greater variability in environmental stress favours trees that prioritise storage of carbohydrate reserves over growth: a modelling analysis

Abstract. Trees use reserves of non-structural carbohydrates (NSC) to help them survive and recover from stress periods. However, accumulation of reserves is at the expense of growth, resulting in a growth-storage trade-off. Tree species may pursue different storage strategies to optimise fitness in environments with differing degrees of stress, but it is not clear which storage strategies provide a competitive advantage in which environments.

We use a forest gap model to explore competitive outcomes among idealised tree species with different combinations of two carbon storage-related traits: carbon utilisation rate (fast-slow spectrum) and switch time from growth to storage (risky-safe spectrum). We investigate the competitive success of alternative growth vs storage strategies in simplified environments which have a non-specific annual stress period. We vary stress intensity (the mean stress duration) and stress stochasticity (the variance of stress duration) to determine the effect of increased stress on composition outcomes.

Community composition shifted from growth-prioritising strategies to storage-prioritising strategies with increasing stress intensity and stochasticity. The major driver of this shift in community composition was increased mortality, due to depletion of carbon reserves, in species with growth-prioritising strategies.

Our results demonstrate that considering carbon storage strategies can provide new insights into tree survival and adaptation of tree communities to increasing stress caused by climate change.