Climate seasonality and tree growth strategies in a tropical dry forest

Abstract

Questions: Do tree species in seasonally dry tropical forests differ in the timing oftheir secondary growth? And in their growth rates between consecutive years? If so,how are these contrasting patterns linked to seasonality in climatic variables (tem-perature, precipitation)? Which is the role of leaf phenology and functional traits asdrivers of stem radial increment responses to climate?Location: A Tumbesian tropical dry forest in southern Ecuador.Methods: We used a 12-year database of stem radial increments to characterizeintra- and inter-annual patterns of secondary growth in 13 co-existing dominant treespecies. For each species, we adjusted an additive model to describe intra-annualincrement patterns and created a mean series of annual increments to describe inter-annual changes. Adjusted increments were then correlated with monthly tempera-ture and rainfall data over the study period, and also with the crown percentagecovered by leaves. The role of functional traits (leaf area, wood density, maximumtree height, seed dry mass) was explored using average trait values per species.Results: We observed continuous variation in the seasonality of radial increments,ranging from species that started incrementing their diameter as early as first rainsoccurred in the season to species that showed delayed responses. Variability in intra-and inter-annual increment patterns was explained by functional traits (leaf area andseed dry mass, and maximum height and wood density, respectively) and leaf phenol-ogy, but this variation was not clearly matched with any functional trait configura-tion. This, combined with the absence of homogeneous responses of annual growthrates to climate, suggests the existence of contrasting strategies that virtually vary ina species-specific fashion.Conclusions: Co-existing tree species in seasonally dry tropical forests show differ-ent growth strategies to face intra- and inter-annual climate variations, which mayincrease the resilience of these forests against projected climatic variations.