Using a trait-based approach to study the relationships between turnover and wood productivity in two contrasting forests of Venezuela, northern South America

Background/Question/Methods

Functional traits can provide insights into a variety of ecological questions within a wide range of scales: from individuals, species, and potentially to communities and landscapes. The main goal of this work is to compare two contrasting forest types in Venezuela, South America, using a trait-based approach to: 1) characterize the functional composition of forests with an emphasis on tree populations; and 2) describe the relationship between the community weighted mean (CWM) of trait values and two ecosystem processes such as wood productivity and aboveground biomass. A group of 15 traits, at different scales (whole-plant, leaf and stem) were measured in the field and/or obtained from selected literature from two areas: Mountain-cloud forests in the Andes (San Eusebio) and Lowland Western plain forests (Caparo). 12 permanent sample plots of 0.25 ha (6 per site) serves as the study area. Between 1 to 5 individuals from a total of 52 tree dominant species (Caparo = 25; San Eusebio = 27) were sampled. To evaluate which predictors among each CWM trait values is the most important for turnover (Tr), wood productivity (WP) and aboveground biomass (AGB), a series of ordinary least squares multiple regression analysis are performed. A general hypothesis being tested is that compared to Andean high elevation forests, Western plain forests are dominated by plant functional types characterized by or acquisitive traits determining a higher productivity and turnover rates.

Results/Conclusions

Both sites had similar values in AGWP (4.56 ± 1.86 Mg C ha^-1 year^-1 in San Eusebio vs 4.32 ± 1.76 for Caparo), but a faster dynamic was found in the lowland forests of Caparo with an average Tr of 2.73 ± 1.11 % year^-1 compared to 1.72 ± 0.70 inSan Eusebio. Contrary to expectations, on average, a higher nitrogen content in soil was found in San Eusebio plots. However, this was not the case for leaf nitrogen where lowland forests had 18% more nitrogen than forests of San Eusebio. The presence of Fabaceae species in Caparo and no record of this family in San Eusebio may be a potential explanation for this. Thicker leaves with a higher chlorophyll content were found at the higher elevation plots. Mean wood density was higher in San Eusebio (0.63 ± 0.25 g cm^-3) and overall well correlated with mortality rates (R² = 0.20) but not with WP. Further tests need to be performed to accurately determine the influence of all traits in forest dynamics.