Changes in the carbon balance of tropical forest: evidence from long-term plots

The role of the world’s forests as a “sink” for atmospheric carbon dioxide is the subject of active debate. Long-term monitoring of plots in mature humid tropical forests concentrated in South America revealed that biomass gain by tree growth exceeded losses from tree death in 38 out of 50 neotropical sites. These forest plots have accumulated 0.71 + 0.34 tons of carbon per hectare per year in recent decades. The data suggest that neotropical forests may be a significant carbon sink, reducing the rate of increase in atmospheric CO2

Population, Land Use and Deforestation in the Pan Amazon Basin: a Comparison of Brazil, Bolivia, Colombia, Ecuador, Perú and Venezuela

This paper discusses the linkages between population change, land use, and deforestation in the Amazon regions of Brazil, Bolivia, Colombia, Ecuador, Perú, and Venezuela. We begin with a brief discussion of theories of population–environment linkages, and then focus on the case of deforestation in the PanAmazon. The core of the paper reviews available data on deforestation, population growth, migration and land use in order to see how well land cover change reflects demographic and agricultural change. The data indicate that population dynamics and net migration exhibit to deforestation in some states of the basin but not others. We then discuss other explanatory factors for deforestation, and find a close correspondence between land use and deforestation, which suggests that land use is loosely tied to demographic dynamics and mediates the influence of population on deforestation. We also consider national political economic contexts of Amazon change in the six countries, and find contrasting contexts, which also helps to explain the limited demographic-deforestation correspondence. The paper closes by noting general conclusions based on the data, topics in need of further research and recent policy proposals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42720/1/10668_2003_Article_6977.pd

Bandages for wounded landscapes: faunal corridors and their role in wildlife conservation in the Americas

The loss and fragmentation of natural habitats is probably the single greatest threat to the world's biological diversity. Fragmentation has a variety of effects including the isolation of habitat remnants, a sharp increase in the amount of habitat edge and, often, a disproportionate loss of certain habitat types - such as accessible areas on fertile, well-drained soils that are most productive for agriculture (Laurance et al. 1999). Wildlife corridors have been advocated as a strategy to lower extinction rates in fragmented landscapes since at least the 1970s (e.g., Willis 1974; Diamond 1975; Wilson and Willis 1975; Wegner and Merriam 1979). By definition, a wildlife corridor is a linear remnant that differs from the surrounding vegetation and connects patches of similar habitat that were more extensively connected in the recent past (Saunders and Hobbs 1991). It is important to emphasize that corridors are not an artificial feature of the landscape, but are intended to help maintain historical habitat connectivity (Noss 1991; Bennett 1999). By facilitating movements of individuals among habitat remnants, corridors can increase population persistence in two ways. First, the demographic and genetic contributions of immigrants can bolster small, dwindling populations in fragments, providing a buffer against local extinction (Brown and Kodric-Brown 1977). Second, if a fragment population should go extinct, immigrants may eventually recolonize the fragment and reestablish the population

Do species traits determine patterns of wood production in Amazonian forests?

Understanding the relationships between plant traits and ecosystem properties at large spatial scales is important for predicting how compositional change will affect carbon cycling in tropical forests. In this study, we examine the relationships between species wood density, maximum height and above-ground, coarse wood production of trees ≥10 cm diameter (CWP) for 60 Amazonian forest plots. Average species maximum height and wood density are lower in Western than Eastern Amazonia and are negatively correlated with CWP. To test the hypothesis that variation in these traits causes the variation in CWP, we generate plot-level estimates of CWP by resampling the full distribution of tree biomass growth rates whilst maintaining the appropriate tree-diameter and functional-trait distributions for each plot. These estimates are then compared with the observed values. Overall, the estimates do not predict the observed, regional-scale pattern of CWP, suggesting that the variation in community-level trait values does not determine variation in coarse wood productivity in Amazonian forests. Instead, the regional gradient in CWP is caused by higher biomass growth rates across all tree types in Western Amazonia. Therefore, the regional gradient in CWP is driven primarily by environmental factors, rather than the particular functional composition of each stand. These results contrast with previous findings for forest biomass, where variation in wood density, associated with variation in species composition, is an important driver of regional-scale patterns in above-ground biomass. Therefore, in tropical forests, above-ground wood productivity may be less sensitive than biomass to compositional change that alters community-level averages of these plant traits