An ecosystem approach to biodiversity effects: carbon pools in a tropical tree plantation. (Special Issue: The ecology and ecosystem services of native trees: implications for reforestation and land restoration in Mesoamerica.)

摘要

This paper presents a synthesis of experiments conducted in a tropical tree plantation established in 2001 and consisting of 22 plots of 45 m x 45 m with either one, three or six native tree species. We examined the changes in carbon (C) pools (trees, herbaceous vegetation, litter, coarse woody debris (CWD), and mineral topsoil at 0-10 cm depth) and fluxes (decomposition of CWD and litter, as well as soil respiration) both through time and among diversity levels. Between 2001 and 2009 the aboveground C pools increased, driven by trees. Across diversity levels, the mean observed aboveground C pool was 7.9+or-2.5 Mg ha-1 in 2006 and 20.4+or-7.4 Mg ha-1 in 2009, a 158% increase. There was no significant diversity effect on the observed aboveground C pool, but we found a significant decrease in the topsoil C pool, with a mean value of 34.5+or-2.4 Mg ha-1 in 2001 and of 25.7+or-5.7 Mg ha-1 in 2009 (F_1,36=52.12, p<0.001). Assuming that the biomass C pool in 2001 was negligible (<1 Mg ha-1), then the plantation gained in C, on average, ~20 and lost ~9 Mg ha-1 in biomass and soil respectively, for an overall gain of ~11 Mg ha-1 over 8 years. Across the entire data set, we uncovered significant effects of diversity on CWD decomposition (diversity: F_2,393=15.93, p<0.001) and soil respiration (monocultures vs mixtures: t=15.35, df=11, p<0.05) and a marginally significant time x diversity interaction on the loss of total C from the mineral topsoil pool (see above). Monthly CWD decomposition was significantly faster in monocultures (35.0+or-24.1%) compared with triplets (31.3+or-21.0%) and six-species mixtures (31.9+or-26.8%), while soil respiration was higher in monocultures than in mixtures (t=15.35, df=11, p<0.001). Path analyses showed that, as diversity increases, the links among the C pools and fluxes strengthen significantly. Our results demonstrate that tree diversity influences the processes governing the changes in C pools and fluxes following establishment of a tree plantation on a former pasture. We conclude that the choice of tree mixtures for afforestation in the tropics can have a marked influence on C pools and dynamics.