Fitness is a function of both environmental characteristics and phenotypic attributes or functional traits that determine the performance of species under varying environmental conditions. One of the key goals of ecology is to understand the factors that determine fitness and its components. Up to now, the relationship between the functional traits and the demographic rates of trees has been studied mostly in tropical species. In this paper we study the association between functional traits, mortality, growth, and climate for 50 widely distributed temperate tree species from Spain, including typical Mediterranean, Sub-Mediterranean and Atlantic species. Functional traits were obtained from the Catalan Ecological and Forest Inventory (IEFC). This inventory included a total of 10,664 plots randomly distributed throughout the forested area of Catalonia, NE Spain (> 1·106 ha of forest). Measured species attributes were maximum tree height, leaf-to-sapwood area ratio, wood density, specific leaf area (SLA), leaf size, nitrogen content of leaves, and seed size. The data on tree growth and mortality rates were obtained from the second and third Spanish National Forest Inventories, which in Catalonia sampled the same plots as the IEFC with a measurement interval of ca. 10 years. Finally, the climatic information was obtained from the digital Climatic Atlas of Spain.
Results/Conclusions
For the studied species, mortality was unrelated to the average climate of their range, whereas growth rates were on average higher for species living in warmer environments. Species attributes, on the other hand, were more influenced by precipitation than by temperature: species from drier regions had lower tree height and tended to have thicker leaves (lower SLA). Regarding the associations between functional traits and demography, growth rate was positively related to maximum tree stature and negatively associated to wood density. Higher mortality rates were observed in species with low wood density and high nitrogen content in leaves. Taller species tended to have larger leaves, higher N contents and lower wood density. Nitrogen content in leaves and SLA were positively related to each other. Our results expand to temperate tree species previous evidence showing that functional traits are good predictors of demographic rates, and show that over a large geographical area differences in demographic rates are more tightly associated to species-specific functional attributes than to differences in climate.
