Inferred causes of tree mortality in fragmented and intact Amazonian forests

In fragmented tropical landscapes, among the most pervasive causes of ecological change are edge effects diverse ecological alterations associated with the abrupt, artificial boundaries of forest fragments (Laurance & Bierregaard 1997, Lovejoy et al. 1986, Turner 1996). A striking edge effect in fragmented Amazonian forests is chronically elevated tree mortality (Ferreira & Laurance 1997, Laurance et al. 1998«). Large (> 60 cm diameter) trees are especially vulnerable to fragmentation, dying three times faster within 300 m of edges than in forest interiors (Laurance et al. 2000). Elevated tree mortality alters canopy-gap dynamics, promotes a proliferation of disturbance-adapted successional species (Laurance et al. 1998fc), reduces above-ground biomass (Laurance et al. 1997), and accelerates litter production (Didham & Lawton 1999, Sizer et al. 2000) and carbon cycling (Nascimento & Laurance, in press). At least three factors could increase tree mortality in tropical forest fragments: (1) Microclimatic stresses: when an edge is created, some trees simply drop their leaves and die standing (Lovejoy et al. 1986, Sizer et al. 2000), apparently because sudden changes in moisture, temperature or light (Kapos 1989, Kapos et al. 1993) exceed their physiological tolerances. (2) Wind damage: some trees are uprooted or snapped by winds, which accelerate over cleared land and then strike forest edges, creating increased windshear and turbulence (reviewed in Laurance, in press). Wind damage is especially