Community assembly responses to warming and increased precipitation in an early successional forest

Abstract

Experimental climate manipulations provide the opportunity to link predicted changes in climate to the process of community assembly. We studied plant community assembly of a recently harvested forest exposed to three years of experimental 2°C warming and 20% increased precipitation. By the end of the experiment, trees were the only functional group that shifted composition in response to warming and precipitation treatments (p = 0.03), while the composition of the grass, forbs, and shrub/small tree/vine functional groups were unresponsive. Individual species within groups were associated with specific treatments, but did not result in a predictable community composition shift. Temporal dynamics of functional group cover were more sensitive to treatment effects than single, static measures of plant community responses such as biomass. Both static and dynamic plant analyses revealed interactive effects of warming and increased precipitation on cover and biomass of grass and all plants together (grass cover p < 0.01, grass biomass p = 0.02, total cover p < 0.01, total biomass p = 0.05). Short forb cover was negatively affected by increased precipitation throughout our experiment (p = 0.03). Grass, tree, and shrub/small tree/vine functional groups showed independent year effects on cover that can be attributed to successional development of the forest community (all p ≤ 0.01). Random forest modeling indicated that cover of other plant functional groups and static plot‐level variables such as plot location and components of soil texture were often the most important predictors of cover for a given functional group, while temperature and moisture availability measures were the least important. Importance of predictors of functional group cover varied greatly among random forest models from different treatments, suggesting that diverse environmental factors constrain functional group cover and may provide resilience of community assembly to climate change.