What's driving regional changes in old-growth tropical forests?
Jeffrey
Q
Chambers, Tulane University, chambers@tulane.edu
(Presenting)
Niro
Higuchi, INPA, niro@inpa.gov.br
Joaquim
dos
Santos, INPA, joca@inpa.gov.br
Liliane
Martins
Teixeira, INPA, liliane@inpa.gov.br
Susan
E.
Trumbore, University of California at Irvine, setrumbo@uci.edu
A number of dramatic changes have been observed in tropical forest structure and functioning. Many of these studies cite the rising concentration of atmospheric CO2 as the most likely driver, but in general these are not rigorous quantitative assessments. Using an individual-based model that simulates tree stand dynamics (recruitment, growth, mortality and decomposition) we explore what factors can explain the observed changes at a regional scale. The model was initially parameterized using extensive field data from forests in the Central Amazon, and has been modified to simulate stand dynamics for sites spanning a productivity and dynamism gradient across the entire Amazon basin. The model has also been modified to include potential drivers for observed changes including: (i) explicitly modeling changes in forest structure and dynamics as a function of the known and expected rise in atmospheric CO2 concentration, (ii) variability in tree recruitment rate and stem density, (iii) changes in wood density and tree community composition, (iv) the effect of elevated mortality on the growth rate of surviving trees, and (v) other potential environmental drivers. Model results demonstrate that for CO2 to be proximal driver, a fertilization sensitivity greatly beyond what has been measured experimentally is required. Conversely, observed changes are much more consistent with relatively catastrophic tree mortality events that occurred sometime shortly before most inventory plots were established. Although it is clear that rising atmospheric CO2 has the capacity to act as a long-term agent of change, observations thus far are much too rapid to have a strong causal link to CO2.
Submetido por Jeffrey Q. Chambers em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)