Equilibrium in plant functional trait responses to warming is stronger under higher climate variability during the Holocene

Abstract

Aim The functional trait composition of plant communities is thought to be determined largely by climate, but relationships between contemporary trait distributions and climate are often weak. Spatial mismatches between trait and climatic conditions are commonly thought to arise from disequilibrium responses to past environmental changes. We aimed to investigate whether current trait–climate disequilibrium is likely to emerge during plant functional responses to Holocene climate warming. Location North America. Time period 14–0 ka. Major taxa studied Terrestrial plants. Methods We joined global trait data with palaeoecological time series and climate simulations on 425 sites. We estimated plant community functional composition for three leaf traits involved in resource use. We then quantified disequilibrium in plant trait temporal responses to climate change during two contrasted periods: a period of high climate variability (14–7 ka) and a period of low climate variability (7–0 ka). Results Functional trait composition showed consistent deviation from climatic equilibrium during both periods. The temporal dynamics of trait composition tends to be positively correlated with climate equilibrium expectations during Holocene climate warming (14–7 ka), but not during a subsequent period of low climate variability (7–0 ka). Main conclusions Long‐term functional responses of plants to climate change showed mixed evidence for both equilibrium and disequilibrium responses. Temporal trait dynamics were closer to the expectations of spatial dynamics under high climate variability, indicating that the relevance of space‐for‐time substitution might be dependent, in part, on climate variability. Our results also suggest that current mismatches between trait and climatic conditions might arise because of a divergence of factors influencing trait dynamics during periods of low climate variability. These findings provide a counterpoint to the common assumption that contemporary trait–climate mismatches result from lagged responses to past climate warming. Our study also demonstrates the need for a deeper investigation of the potential influence of non‐climatic factors on functional plant community dynamics.

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