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

Aim.The functional trait composition of plant communities is thought to be largely determined 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 here investigated whether current trait-climate disequilibrium were likely to emerge during plant functional responses to Holocene climate warming. Location.North America Time period.14-0Kya Major taxa studied. Terrestrial plants Methods. We joined global trait data with paleoecological 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 Kya), and a period low climate variability (7-0 Kya). Results. Functional trait composition showed consistent deviation from climatic equilibrium during both periods. The temporal dynamics of trait composition tends to be positively correlated to climate equilibrium expectations during Holocene climate warming (14-7 Kya), but not during a following period of low climate variability (7-0 Kya). 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 spatial dynamics expectations under high climate variability, indicating that relevance of space-for-time substitution might be partially dependent on climate variability. Our results further suggest that current mismatches between trait and climatic conditions may arise due to a divergence of factors influencing trait dynamics during low climate variability periods. 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.