Leaf nitrogen and wood density, but not root traits, explain the growth and survival of temperate tree species

Abstract The interspecific trade‐off between tree growth potential in resource‐rich environments and survival in resource‐poor ones is a central element of species' distributions and forest diversity. Above‐ground traits are commonly used to understand demographic strategies of tree species, but research on root trait relationships with tree growth and especially survival is largely lacking. This study is among the first to investigate how leaf, wood and root traits influence growth in resource‐rich environments and survival in poor environments across temperate tree species. A dataset of over 735,000 observations of tree‐level growth and survival was compiled for more than 370,000 trees of 15 temperate species growing in the northeastern United States, and censused between 2000 and 2014. Species' data on leaf, stem and root traits commonly deemed important for tree demography (i.e. leaf nitrogen [N], specific leaf area [SLA], wood density [WD], specific root length [SRL] and root N) were retrieved from trait databases. These above‐ and below‐ground traits were used in a causal analytical framework combined with Bayesian multilevel models to understand their relationships with tree demography. We found that high leaf N and low WD resulted in faster growth under favourable conditions, and in lower survival in unfavourable environments. SLA and SRL had weaker and less clear negative effects on tree growth and positive effects on tree survival. There was no clear evidence of root N effects on growth or survival. Synthesis— Our work shows that the root traits included in this study had weak and no clear effect on tree species' demography. The relative importance of different root traits for tree growth and survival may be contingent on the soil environment, so that species' demographic strategies cannot be confidently inferred from below‐ground traits without biotic or abiotic environmental context.