Altered leaf-litter decomposition rates in tropical forest fragments

Abstract

The effects of forest fragmentation on leaf-litter decomposition rates were investigated for the first time in an experimentally fragmented tropical forest landscape in Central Amazonia. Leaf-litter decomposition rates were measured at seven distances (0-420 m) along forest edge-to-interior transects in two 100-ha fragments, two continuous forest edges, and at an identical series of distances along two deep continuous forest transects, as well as at the centers of two 1-ha and two 10-ha fragments. Decomposition rates increased significantly towards the edge of 100-ha forest fragments. Litter turnover times were 3-4 times faster within 50 m of the edge of 100-ha fragments than normally found in deep continuous forest. In contrast, there was no significant change in the rate of leaf-litter decomposition from the interior to the edge of continuous forest. It is difficult to account for these very different edge responses. Decomposition rates were not correlated with air temperature differentials, evaporative drying rates, litter depth, biomass or moisture content, or with total invertebrate densities, either within individual edge transects or across all sites. The difference in edge response may be due to chance, particularly the patchy removal of vast quantities of litter by litter-feeding termites, or may be a real, area-dependent phenomenon. Clearly, however, forest fragmentation increases the variability and unpredictability of litter decomposition rates near forest edges. In addition to edge effects, decomposition rates were strongly affected by decreasing fragment area. While sites at the centers of 10-ha and 100-ha forest fragments and continuous forest had equivalent decomposition rates, rates were markedly lower at the centers of 1-ha fragments. Litter turnover times were 2-3 times slower in 1-ha fragments than in continuous forest, and up to 13 times slower than at 100-ha edges. Litter structure and nutrient cycling dynamics are inevitably altered by forest fragmentation.

Influence of habitat, litter type, and soil invertebrates on leaf-litter decomposition in a fragmented Amazonian landscape

“…However, for similar organic materials, decomposition rates were virtually the same across the different habitats, indicating that among-habitat differences in microclimate were not sufficiently large to affect decomposition. In fact, previous studies indicate that abiotic edge gradients in air temperature, evaporative drying rate, and littermoisture content in fragmented forests do not correlate with leaf-litter decomposition rates (Didham 1998). Similarly, studies on tropical forest succession have found little or no effects of the forest physical environment on litter decomposition.…”

“…Hence, although mounting evidence suggests that litter-decomposition rates in Amazonian forests can be affected by recent anthropogenic disturbances (Didham 1998), critical experiments are still missing. We compared rates of litter decomposition among three forest habitats representing a gradient of increasing disturbance and drier microclimatic conditions.…”

Produção de serapilheira em diferentes fases sucessionais de uma floresta subtropical secundária, em Antonina, PR

“…Representando uma ligação importante no ciclo orgânico de produção-decomposição, a serapilheira tem papel fundamental no funcionamento do ecossistema fl orestal (MEENTEMEYER et al, 1982). Dessa forma, seu estudo pode fornecer índices de produtividade da fl oresta, noções sobre taxas de decomposição e fenologia das espécies, além de permitir avaliar sua importância nos ciclos de nutrientes (CUNHA et al, 1993;DIDHAM, 1998;PROCTOR et al, 1983).…”

Ecosystem decay of Amazonian forest fragments: implications for conservation

“…Microclimatic changes near edges, such as reduced humidity, increased light, and greater temperature variability, penetrate up to 60 m into fragment interiors (Kapos 1989) and can negatively affect species adapted for humid, dark forest interiors (Lovejoy et al 1986, Benitez-Malvido 1998. Leaf litter accumulates near edges (Carvalho and Vasconcelos 1999 Edge penetration distance (m) Didham and Lawton 1999) because drought-stressed trees shed leaves and possibly because drier edge conditions slow litter decomposition (Kapos et al 1993, Didham 1998, Vasconcelos and Laurance 2005. Accumulating litter may negatively affect seed germination (Bruna 1999) and seedling survival (Scariot 2001) and makes forest edges vulnerable to surface fires during droughts (Cochrane et al 1999).…”

“…There is a dramatic pulse in tree mortality; many trees die standing (Laurance et al 1998b). Leaflitter accumulates as drought-stressed trees shed leaves to conserve water, or replace shade-adapted leaves with sun-adapted leaves (Didham 1998). Abundances of many animals fluctuate sharply.…”