Biological impacts of deforestation and fragmentation
- Physical consequences of deforestation.
- Habitat loss and insularization.
- Abiotic changes in forest fragments.
- Biological consequences of fragmentation.
- Changes in individual physiology and behavior.
- Changes in population size and genetic structure.
- Changes in community composition and their consequences.
- Changes in ecosystem dynamics.
- Conclusion- Future directions.
In addition to housing the majority of the planet's biodiversity, forest ecosystems are the basis for trillions of dollars in global revenue. They are homes to indigenous groups, sources of food, medicines, and raw materials for industry, and they provide opportunities for recreation and tourism. They are also being logged, cleared, or otherwise altered by humans at alarming rates. Consequently, understanding the physical and biological consequences of deforestation has become one of the leading areas of research in forest ecology. This review aims to describe the physical and biological consequences of deforestation on four levels of ecosystem organization: individuals, populations, communities, and ecosystems. The most dramatic and immediately obvious consequence of deforestation is the loss of native habitat in newly cleared areas. However not all deforestation results in the denuded landscapes one typically associates with clear-cut logging or industrial cattle ranching. In many cases deforestation proceeds unevenly, leaving behind a patchwork of forest fragments that are isolated at varying degrees from one another.
[...] Changes in Ecosystem Dynamics Deforestation and fragmentation can also in?uence ecosystem processes at fragment, landscape, or continental scales. Within fragments, nutrient cycling can be substantially altered, since there is an increase in the amount of leaf litter on the forest ?oor and this litter often takes longer to decompose. At the regional scale, fragmentations can in?uence temperature and rainfall patterns. It is estimated that as much as 50% of rainfall in the parts of the Amazon is produced by the respiration of trees, and that by removing half the forest and replacing it with pastures total rainfall could be reduced by as much as 25%. [...]
[...] Many amphibians, insects, small mammals, and plants are habitat generalists tolerant of a broad range of habitat types. In some cases species diversity even increases despite the loss of forest-interior species, because their absence is compensated by an in?ux of generalists from the surrounding matrix. Perhaps one of the best examples of this phenomenon is tropical pool-breeding frogs, of which disturbed-habitat specialists (e.g., Scinax rubra, Adenomera hylaedactyla) can be found in recently isolated forest fragments and on the edges of continuous forest. [...]
[...] Fragments surrounded by activities that maintain sharp fragment borders, such as cattle ranching or wheat farming, remain continually exposed to altered environmental conditions. Conditions in fragments can eventually return to levels similar to those found prior to fragment isolation, if cleared areas are allowed to regenerate or if agroforestry and other less intense forms of land use are adopted. Biological Consequences of Fragmentation Changes in Individual Physiology and Behavior As might be expected, the dramatic environmental changes in fragments can have serious consequences for the physiological condition of individuals that live there. [...]