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The concept of biological diversity, or biodiversity, encompasses the variety of existing life forms, the ecological roles they perform, and the genetic diversity they contain. The extent of biodiversity is typically viewed as a measure of ecosystem health, with more diverse ecosystems generally being more stable, productive and resistant to invasion and other disturbances.
Human life also relies on biodiversity for sustenance, health, well-being and enjoyment. All food and many medicines and industrial products are derived from wild and domesticated components of biological diversity. Biodiversity is also the basis for much of our recreation and tourism, and includes the ecosystems which provide services such as clean water.
Forests, and especially primary forests, tend to be more biologically diverse than other terrestrial landscapes and make significant contributions to broader ecosystem functioning. It is now recognised that much of the human exploitation of forests has been at the expense of biodiversity and the natural regulation of ecosystem functions, for example, with respect to water, climate and carbon storage.
Biodiversity is in part a function of climate, and generally there is an increase in species from the poles to the Tropics. Tropical forest ecosystems host at least two-thirds of the Earth’s terrestrial species and provide significant local, regional and global human benefits from the provision of economic goods and ecosystem services.
The future of many tropical forest species is uncertain. Few areas of the Tropics have escaped human impacts, and the combined influence of high rates of deforestation, degradation, over-harvesting, invasive species and global environmental change threatens to make tropical forests the centre of current and future extinctions. The future of much tropical forest biodiversity therefore depends on effective management of human impacts on these ecosystems.
Globally, there was around 4.0 billion hectares of forest in 2010, down from 4.2 billion hectares in 1990. Losses in the Tropics were around 9.5 million hectares per annum, and the Rest of the World reported an increase of 2.7 million hectares (0.1%) per annum due to the expansion of planation forests.
However, in terms of biodiversity, a focus on changes in the total forest area will overlook the fact that not all forests are the same. In the Tropics, primary forests have been shown to host the greatest biodiversity, followed by selectively logged forests, secondary forests and plantation forests. That is, a transition from primary forest to degraded forest through selective logging or other practices will affect diversity without deforestation, while plantations will add to the stock of forests but will host less biodiversity. It is important to consider these factors when assessing changes in the type of forest cover on biodiversity.