Tree growth is one of the most fundamental factors to understand population dynamics in tree communities. Factors that influence tree growth are those that maximize the tree’s ability to capture, store, energy and nutrient use . Climate variables such as temperature and precipitation provide the raw materials needed for growth. Functional traits, such as seed mass and nutrient content, represent the tree’s capacity to make use of these resources. We examined the effect of climate and functional traits on tree growth in forests communities. We used forest inventory data from four temperate and two tropical forests where all trees with > 1 cm diameter of breast height were measured during 4-5 years. Each forest location has 5 plots, where annual growth rates were estimated. In each of these plots, functional traits of the dominant species (species that account for at least 70% of total biomass) were measured in the 2015-2016. where tree growth, where all the species that account for over 70% of basal area. Traits related with nutrient and carbon uptake were measured. These traits included specific leaf area (SLA), foliar carbon (LCC), seed mass (SM), leaf carbon (LNC) and nitrogen concentrations (LNC) and their stable isotopes (d13C, d15N). We expected tree growth to increase with foliar nutrients, SLA, and with temperature. Thus, growth rates were expected to be higher in tropical than temperate forests.
We found tree growth to have significant links with incoming solar radiation, wind speed, potential evapotranspiration, mean annual precipitation (MAP), the ratio of potential evapotranspiration and mean annual precipitation, mean annual temperature (MAT), and soil temperature. Among these climatic factors, the most important were MAP, MAT and soil temperature. Contrary to our expectations, SLA did not have any effect on annual growth rates. Growth rates were strongly influenced with climate and only few traits were as important as climate, such as leaf nitrogen stable isotope (d15N), LCC and LNC. The importance of water use efficiency traits for tree growth is remarkable given the broad variation in climatic gradients, which suggest that other traits related to physiology rather than resource acquisition may play an important role in annual carbon gain. Overall growth rates were higher in tropical forests compared to temperate forests related with warmer and wetter environments. Future analysis should incorporate the indirect effects of climate on functional traits to disentangle the main drivers of tree growth in each forest site.