FIRE IN THE BRAZILIAN AMAZON .1. BIOMASS, NUTRIENT POOLS, AND LOSSES IN SLASHED PRIMARY FORESTS

Deforestation in the Brazilian Amazon has resulted in the conversion o f > 230,000 km(2) of tropical forest, yet little is known on the quant ities of biomass consumed or the losses of nutrients from the ecosyste m. We quantified the above-ground biomass, nutrient pools and the effe cts of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha(-1) to 436 Mg ha(-1). Coarse wood debris (> 20.5 cm diamete r) was the dominant fuel component. However, structure of the four sit es were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 t o 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of > 99% of the litter and rootmat, yet < 50% of the coarse wood debris. Dramatic losses in C, N and S wer e quantified. Lesser quantities of P, K, and Ca were lost by combustio n processes. Carbon losses from the ecosystem were 58-112 Mg ha(-1). N itrogen losses ranged from 817 to 1605 kg ha(-1) and S losses ranged f rom 92 to 122 kg ha(-1). This represents losses that are as high as 56 %, 68%, and 49% of the total above-ground pools of these nutrients, re spectively. Losses of P were as high as 20 kg ha(-1) or 32% of the abo ve-ground pool. Losses to the atmosphere arising from primary slash fi res were variable among sites due to site differences in concentration , fuel biomass, and fuel structure, climatic fluctuations, and anthrop ogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the hig hest total losses of nutrients ever measured. In addition, the proport ion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.