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 Niño years has important implications for the global carbon cycle due to substantial carbon stores in their biomass. This study reports on plant mortality (stems ³2 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 ³30 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 ³10 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 Científico do LBA: CD (Armazenamento e Trocas de Carbono)