Drought Effects on Plant Mortality, Forest Structure, and Dead Biomass Pools in an Eastern-Central Amazonian Rainforest: Results of a Partial Throughfall Exclusion Experiment
Ingrid
Marisa
Tohver, Instituto de Pesquisa Ambiental da Amazonia, marisa@ipam.org.br
(Presenting)
David
Ray, Woods Hole Research Center, dray@whrc.org
Daniel
Curtis
Nepstad, Woods Hole Research Center, dnepstad@whrc.org
Paulo
Roberto
Moutinho, Instituto de Pesquisa Ambiental da Amazonia, moutinho@ipam.org.br
Elevated levels of plant mortality in tropical rainforests provoked by severe droughts during El Ni�o years has important implications for the global carbon cycle due to substantial carbon stores in their biomass. This study reports on plant mortality (stems �2 cm dbh) following four years of simulated drought in a throughfall exclusion experiment in an east-central Amazon forest. Fifty percent of incoming precipitation was excluded from the soil of an 1-ha dry plot (D) during the 6 month wet season, and was compared to the 1-ha wet plot (W). Plant available water in the upper 11 m of the soil profile was reduced to <10% of capacity in the D plot. Community wide mortality rates, 2.72% yr-1 (W) and 3.77 % yr-1 (D), indicate a 38% increase due to the treatment (P<0.001). Trees �30 cm dbh endured higher levels of drought-induced mortality (W=1.74% yr-1, D=9.47% yr-1; P=0.005) than stems 2-5 cm dbh (W=2.77% yr-1, D=3.16% yr-1; P=0.126). Woody vines suffered higher drought-induced mortality rates (W=3.78% yr-1, 6.78% yr-1; P=0.004) than either trees or palms. Mortality rates of overstory canopy tree species were over twofold in the dry plot (W=1.75% yr-1, D=3.80% yr-1; P<0.001), whereas mid-canopy and understory species remained unaffected. Stems �10 cm dbh accounted for 90% of the pre-treatment live aboveground biomass in both plots (278 Mg ha-1). Our measurements indicate that drought-induced mortality of large trees resulted in a net increase of 7.0 Mg C ha-1 yr-1 (~5% of aboveground standing biomass) of committed emissions to the atmosphere.
Submetido por Margaret Rose Francis em 18-MAR-2004
Tema Cient�fico do LBA: CD (Armazenamento e Trocas de Carbono)