Fire as a large-scale edge effect in Amazonian forests

Abstract

ABSTRACT. Amazonian forests are being rapidly cleared, and the remaining forest fragments appear unusually vulnerable to fire. This occurs because forest remnants have dry, fire-prone edges, are juxtaposed with frequently burned pastures, and are often degraded by selective logging, which increases forest desiccation and fuel loading. Here we demonstrate that in eastern Amazonia, fires are operating as a large-scale edge effect in the sense that most fires originate outside fragments and penetrate considerable distances into forest interiors. Multitemporal analyses of satellite imagery from two frontier areas reveal that fire frequency over 12-14-y periods was substantially elevated within at least 2400 m of forest margins. Application of these data with a mathematical core-area model suggests that even large forest remnants (up to several hundred thousand ha in area) could be vulnerable to edge-related fires. The synergistic interactions of forest fragmentation, logging and human-ignited fires pose critical threats to Amazonian forests, particularly in more seasonal areas of the basin.

Changes in plant community diversity and composition across an edge between Araucaria forest and pasture in South Brazil

“…In this study grazing and cattle trampling may have caused differential mortality of herbs and woody seedling as observed by Mauhs & Backes (2002) in a similar study area. Additionally, the occasional penetrations of fire may cause significant changes in vegetation structure and composition at the edge affected area that in this study penetratres, at least, up to 50 m inside the forest (Cochrane & Laurance 2002). Another factor of great importance that we have observed was the action of strong sporadic winds that caused great damage to vegetation and high mortality of canopy trees at the edge.…”

When bigger is better: the need for Amazonian mega-reserves

“…One of the most compelling justifications for megareserves is that destructive surface fires, frequently lit by ranchers and farmers, can operate as a large-scale edge effect, penetrating up to several kilometers into forests during drought years [20]. Simulation models suggest that even large (O100 000 ha) reserves can be vulnerable to such fires [20].…”

“…Simulation models suggest that even large (O100 000 ha) reserves can be vulnerable to such fires [20]. These considerations highlight the importance not only of maximizing reserve size, but also for maintaining fire-free buffer zones around reserves and limiting roads inside reserves, which can facilitate forest invasions and fires.…”

Rapid land-use change and its impacts on tropical biodiversity

“…In most human-dominated landscapes, the large majority of forest fragments are small, ranging from <1 ha to a few hundred ha in area [Gascon et al, 2000;Peres, 2001;Cochrane and Laurance, 2002]. Rates of local extinction are usually high in such fragments, which sustain small population sizes of many species.…”

“…This occurs because forest remnants have dry, fire-prone edges, are juxtaposed with frequently burned pastures or slash-and-burn farming plots, and are often degraded by selective logging, which increases forest desiccation and fuel loading. In a fragmented landscape in eastern Amazonia, surface-fire incidence was significantly increased (Figure 4)[AC4] within 2400 m of forest edges and sharply elevated within 600-800 m of edges [Cochrane and Laurance, 2002]. Because rainforest vegetation is especially vulnerable to burning, a single surface fire can cause an extensive dieback of forest margins whereas recurring fires may lead to fragment "implosion" [Gascon et al, 2000].…”