Functional trait shifts after disturbance reveal broad‐scale variability in temperate forest regional recruitment processes

Abstract

AbstractQuestionDecreased above‐ground biomass and subsequent changes in resource availability exert a strong influence on seedling recruitment in post‐disturbance forests. Ecological trade‐offs underlie recruitment processes, as species vary in resource allocation, dispersal and stress tolerance strategies. Functional traits that indicate resource acquisition–conservation trade‐offs include leaf N content, wood density, maximum height, shade tolerance and drought tolerance, while seed mass can indicate species’ dispersal strategies. This study looks for generality in post‐disturbance trait responses, and asks whether these responses are additionally constrained or amplified by disturbance characteristics, climate and ecological provinces.LocationEastern US temperate forests.MethodsI leveraged a longitudinal, continental‐scale database of post‐disturbance forests to examine recruitment dynamics. Using multivariate, hierarchical Bayesian models, I examined how disturbance affects the traits of seedling layer communities where recruitment dynamics should be most evident, and compared this to undisturbed communities. I also examined how the traits underlying trade‐off axes varied across disturbance properties, ecological provinces and climatic gradients.ResultsAll traits except leaf N showed significant, study‐wide shifts in disturbed communities consistent with expectations of post‐disturbance stands. In undisturbed plots, all traits had significant shifts in the opposite direction to those observed in disturbed plots, except leaf N and drought tolerance, where no change was observed. Disturbance severity increased the magnitude of response of several, but not all, trait responses in disturbed plots. The traits that had significant shifts were idiosyncratic across ecological provinces, indicating unique processes influencing disturbance responses across the system. Moreover, while climate strongly correlated with all traits prior to disturbance in the initial sampling periods, it was not correlated with disturbance responses.ConclusionsThis study demonstrates general, biome‐wide trait shifts towards resource acquisition and bet‐hedging dispersal strategies in post‐disturbance forest seedling communities. At finer spatial scales, the traits underlying these trade‐offs varied, indicating that disturbance‐dependent species differ in life‐history strategies across the system. This variation across ecological provinces appears independent of temperature and precipitation, suggesting that unmeasured abiotic or biotic variables influence recruitment. Seedling recruitment is critical in shaping future adult tree communities, and this study reveals large‐scale contingencies in trait patterns associated with this process.