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date: 20 July 2019


This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.

Eight thousand years ago, forests covered an estimated 47% of Earth’s land surface. In 2015, forests covered roughly 30% of the Earth’s land surface, a cumulative loss over the last 8,000 years of approximately 2.2 billion hectares (ha). Between 1990 and 2015, forest losses occurred at the rate of about 0.13% annually, but this rate appears to be slowing. These losses mostly occur in tropical forests (58%), followed by boreal (27%) and temperate forests (8%). Deforestation is driven by a number of direct and indirect factors and processes that vary across regions and interact in complex ways. The primary driver of deforestation is agricultural expansion (both commercial and subsistence), followed by mining, infrastructure extension, and urban expansion. Indirectly, population and economic growth increase the demand for agricultural and timber products. Global food demand will increase 70% by 2050, requiring a net increase of 70 million ha of arable land under cultivation, with approximately 80% of this expansion occurring in the tropics. Deforestation is affected by other indirect factors such as land tenure uncertainties, poor governance, low capacity of public forestry agencies, and inadequate planning and monitoring. Forest loss has a number of environmental, economic, and social implications. Environmentally, forests provide an expansive range of benefits across local, regional, and global scales, including hydrological benefits (e.g., regulating water supply and river discharge), climate benefits (e.g., precipitation recycling, regulating local and global temperature, and indirectly, by taking up atmospheric CO2 during photosynthesis), biogeochemical benefits (e.g., enhancing nutrient availability and reducing nutrient losses), and by supporting greater biodiversity as well as ecosystem stability and resiliency, to name a few. The loss of forest vegetation may negatively affect important ecosystem processes and services, and may induce bistable ecosystem dynamics. The existence of bistable ecosystem dynamics in some forest ecosystems suggests that these forests are prone to abrupt and irreversible shifts to a stable and often degraded state with no trees. In addition to environmental impacts, the long-term loss of forest resources negatively affects societies. About 8% (450 million) of the world’s population live in forest ecosystems, with an estimated 350 million people entirely dependent on forest ecosystems for their livelihoods. The forest sector, in 2011, contributed an estimated total amount of USD 600 billion to global GDP, or about 0.9% of global GDP. Understanding how to best manage forest resources to preserve their unique qualities is a challenge that will require an integrated and concentrated effort from scientists and policymakers alike. In particular, improving forest management will require being able to more accurately measure and monitor forest resources, identifying the trade-offs between competing objectives, valuing forest goods and services, and equitably balancing costs and benefits. On the policy front, approaches to strengthen land tenure and property rights, reduce corruption, improve the capacity of public agencies, and develop more inclusive governance arrangements are needed. Underlying these management and policy goals is the need to better understand the environmental processes occurring in forests—to improve their management, minimize adverse impacts, and strengthen our models of these systems, because the long-term loss of forest resources affects not only the functioning of ecosystems but also the societies whose health and livelihoods depend upon them.