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Unprecedented rates of deforestation and biomass burning in tropical dry forests are dramatically influencing biogeochemical cycles, resulting in resource depletion, declines in biodiversity, and atmospheric pollution. We quantified the effects of deforestation and varying levels of slash-fire severity on nutrient losses and redistribution in a second-growth tropical dry forest ([open quotes]Caatinga[close quotes]) near Serra Talhada, Pernambuco, Brazil. Total aboveground biomass prior to burning was [approx]74 Mg/ha. Nitrogen and phosphorus concentrations were highest in litter, leaves attached to slash, and fine wood debris (

In the state of Para, Brazil, in the eastern Amazon, the authors studied the potential for sustained fire events within four dominant vegetation cover types (undisturbed rain forest, selectively logged forest, second-growth forest, and open pasture), by measuring fuel availability, microclimate, and rates of fuel moisture loss. They also estimated the potential tree mortality that might result from a wide-scale Amazon forest fire by measuring the thermal properties of bark for all trees in a 5-ha stand of mature forest, followed by measurements of heat flux through bark during simulated fires. In pastures the average midday temperature was almost 10{degree}C greater and the average midday relative humidity was 30% lower than in primary forest. The most five-prone ecosystem was the open pasture followed by selectively logged forest, second growth forest, and undisturbed rain forest in which sustained combustion was not possible even after prolonged rainless periods. Even though the autogenic factors in primary forest of the eastern Amazon create a microclimate that virtually eliminates the probability of fire, they are currently a common event in disturbed areas of Amazonia. As many as 8 {times} 10{sup 6} ha burned in the Amazon Basin of Brazil in 1987 alone. In terms ofmore » current land-use patterns, altered microclimates, and fuel mass, there are also striking similarities between the eastern Amazon and East Kalimantan, Indonesia (the site of recent rain forest wildfires that burned 3.5 {times} 10{sup 6} ha).« less

Tropical secondary forests have the capacity to function as large carbon and nutrient sinks and may offset losses resulting from deforestation and land use. In the heavily deforested Los Tuxtlas Region of Mexico, aboveground biomass as well as aboveground and mineral soil C, N, S, and P pools were quantified in 11 secondary forest sites. These sites ranged in age from 6 mo to 50 yr following abandonment and had experienced between 1 and 30 yr of land use prior to abandonment. Total aboveground biomass (TAGB) increased with increasing site age and ranged from 4.8 Mg/ha in a recently abandoned site to 287 Mg/ha in the 50-yr-old secondary forest site. Results indicate that secondary forests would reach TAGB levels equivalent to those of primary forests in the Los Tuxtlas Region after 73 yr. Furthermore, mean annual aboveground biomass accumulation (ABA) of secondary forests was strongly and inversely related to the duration of prior land use. Aboveground pools of C, N, S, and P were also positively correlate...