Forest structure and species traits mediate projected recruitment declines in westernUStree species

Abstract

AbstractAimDetermine if differences in the climatic niche between conspecific adult and juvenile trees of the westernUnitesStates vary by species traits and to assess if forest canopies moderate the sensitivity of juvenile trees to climatic variation.LocationThe westernUnitesStates.MethodsUsing data from theUSDA ForestInventory andAnalysis programme, we compare the distribution of conspecific adult and juvenile trees for 62 westernUStree species. We relate demographic niche differences to species traits including shade and drought tolerance. We model recruitment under projected climate change using generalized linear mixed models, probabilistic uncertainty accounting, forest structural data and projected changes in the climatic water balance.ResultsOn average juveniles of westernUStree species occupy a climatic subset of their conspecific adults. Demographic niche differences increase as species shade and drought tolerance increase and are greatest at climatic range margins, indicating the potential for range contractions. Models calibrated solely with climate data project recruitment declines for 2080 that are 47% larger on average than models that also account for forest structure.Main conclusionsClimate change‐driven declines in recruitment in westernUStree species may be partly offset by the moderating effect of forest canopies. The importance of this stabilizing process will depend on whether a given site is disturbed and the traits of resident species, including their ability to utilize sites that have buffered microclimates. Conversely, our results suggest that broad‐scale disturbances which result in the loss of forest canopy will amplify the effects of climate change on tree recruitment.