Linking functional traits with tree growth and forest productivity in Quercus ilex forests along a climatic gradient

Plant functional traits are highly adaptable to changes in climatic factors and nutrient availability. However, the intraspecific plant response to abiotic factors and the overall effect on plant growth and productivity is still under debate. We studied forest productivity for 30 Quercus ilex subsp ballota forests in Spain along a broad climatic gradient of aridity (mean annual precipitation from 321 to 1582 mm). We used linear mixed models to quantify the effect of climatic and edaphic factors on functional traits, and to study the effect of functional traits and abiotic factors on the relative growth rate (RGR) of adult trees. Then we used piecewise structural equation models (SEMs) to determine the causal effect of intrinsic and extrinsic factors on forest productivity. Our results showed that forest productivity is positively affected by forest biomass and RGR, which are mainly affected by functional traits and tree biomass, respectively. In conclusion, intraspecific variability of functional traits have a significant effect on plant biomass and growth, which ultimately explain forest productivity in Quercus ilex.