A Disturbing Synergism Between Cattle Ranch Burning Practices and Selective Tree Harvesting in the Eastern Amazon

Abstract

The combination of pasture burning to control weeds and selective timber harvesting is resulting in the spread of wildfires in Amazonian rain forests near Paragominas, Para, Brazil. We visited 15 cattle ranchers who had permitted selective logging on their land and found that eight of the affected forests had burned shortly after logging. In selectively logged, high forests, fire-induced mortality was greatest for trees less than 10 cm DBH, whereas in low and second-growth forests, nearly all trees were killed. Fires affect regeneration mechanisms such that the more severely forests are burned, the more complex and prolonged will be the pattern of succession. OF ALL THE OPTIONS FOR ECONOMIC DEVELOPMENT in the Amazon region, the selective harvest of valuable timber species on a rotational basis is one of the most ecologically sound (Goodland 1980, Fearnside 1983). Selective tree harvesting, when done carefully, usually creates three to six canopy gaps per hectare which are akin to natural forest tree fall disturbances. Regeneration following natural tree falls is rapid (Brokaw 1984, Whitmore 1983). Pre-existing seedlings and saplings (advance regeneration) and fast-growing pioneer trees, usually originating from seeds buried in the soil, dominate the regrowth. Moreover, because only the nutrient-poor boles are removed (i.e., the relatively nutrient-rich twigs, leaves, and roots remain) and because regeneration is rapid, nutrient loss is probably inconsequential. Although regeneration occurs rapidly without further disturbance, selective tree harvesting leaves the forest in an open, fuel-rich, fire-prone state. We have observed that fires set to control weeds in degraded pastures in eastern Amazonia commonly spread into adjacent forests. Fire readily spreads through exploited (selectively logged) forests causing extensive damage, but fires reaching the edge of unexploited forests quickly die out. Thus, the effects of forest timber removal and pasture burning interact to produce more detrimental effects than either pro-