Tropical Forest – Ecological And Socio
Edited by B. L. Turner, Arizona State University, Tempe, AZ, and approved July 30, 2010 (received for review September 22, 2009)
Abstract
Global demand for agricultural products such as food, feed, and fuel is now a major driver of cropland and pasture expansion across much of the developing world. Whether these new agricultural lands replace forests, degraded forests, or grasslands greatly influences the environmental consequences of expansion. Although the general pattern is known, there still is no definitive quantification of these land-cover changes. Here we analyze the rich, pan-tropical database of classified Landsat scenes created by the Food and Agricultural Organization of the United Nations to examine pathways of agricultural expansion across the major tropical forest regions in the 1980s and 1990s and use this information to highlight the future land conversions that probably will be needed to meet mounting demand for agricultural products. Across the tropics, we find that between 1980 and 2000 more than 55% of new agricultural land came at the expense of intact forests, and another 28% came from disturbed forests. This study underscores the potential consequences of unabated agricultural expansion for forest conservation and carbon emissions.
Đang xem: Tropical forest
Global demand for food, feed, and fuel is increasing at unprecedented rates, but the agricultural land base needed for production is shrinking in many parts of the world (1–3). Population increases and rapidly rising meat consumption were forecasted to increase global agricultural demands dramatically (3, 4), even before the spike in the use of crop-based biofuels.
This situation raises the question: How will the increasing demand for agricultural products be met? Increases in crop yield will be a critical component in meeting these needs, but the projected ∼1–2% annual increases probably will not be enough to match the rapidly mounting demand for agricultural commodities (5). Some studies consider these projected yield increases overly optimistic (6) and expect they will decline over the next 10 y to less than 1% per y in some regions (7). Even with yield increases and intensification, we will see net expansion in agricultural area (8).
Consequently, much of the world is looking toward the remaining areas of arable land in the tropics to meet increasing agricultural demands (2, 4, 9–11). Lower production costs and fewer environmental regulations have helped forest-rich tropical countries such as Brazil, Indonesia, and Malaysia respond quickly to increased demand for crops such as sugarcane, soybeans, and oil palm (12–14). Indeed, the expansion of the global agricultural land area during the 1980s and 1990s occurred primarily in developing countries where total agricultural land (croplands, pastures, and temporary agriculture) increased by 629 million ha while developed countries lost 335 million ha (4, 14). For example, soybeans now cover more than 21 million ha in Brazil, up from just 13 million ha at the turn of the century (14). Similarly, Indonesia’s oil palm production nearly tripled during the 1990s, with the harvested area expanding from 2 million ha in 2000 to 5 million ha in 2008 (14, 15). Brazil, Indonesia, and Malaysia combined now produce more than 40% of the world’s sugarcane, soybeans, and oil palm (14), and this proportion is expected to increase.
Total cultivated land area undoubtedly will expand across the tropics, and some estimate that as many as 10 billion new ha of agricultural land will be needed to sustain global demands by 2050, more than doubling the current agricultural land base (3, 4, 14). Demands for animal fodder and biofuels alone have been projected to drive increases in soy and sugarcane acreage in Brazil from 28 million ha today to 88–128 million ha by 2020 (16). Similarly, oil palm estates in Indonesia are estimated to grow from 6.5 million ha to 16.5–26 million ha during this period (16).
Xem thêm: Top 10 Nhà Xe Bình Dương An Giang Châu Đốc Limousine Giường Nằm
The environmental impacts of this unprecedented expansion of tropical croplands and pastures will vary widely, depending on the types of land being cleared and cultivated. Agricultural expansion is a major driver of tropical deforestation (17–20), but not all expansion results in the loss of intact forests: shrublands, pasture, logged or regrowing forests, degraded land, and shifting cultivation fields are all sources for new permanent agriculture (21–23). It is critical to understand the geographic and temporal differences in expansion pathways to quantify the impacts on all ecosystems services, including carbon storage, wildlife habitat, and watershed benefits.
Scientific descriptions of these expanding agricultural lands—and whether they arise from new deforestation or from previously cleared lands—are surprisingly absent and remain largely undocumented for the tropics as a whole. Progress in environmental governance and policy decisions (e.g., domestic and international standards for renewable fuel) is hindered by sparse information on land sources for newly expanded croplands. Indeed, debate continues to mount about the landscape origins of global agricultural commodities such as oil palm, sugarcane, and soybeans. Agro-industrialists and some scientists suggest that expansion is occurring largely on degraded or previously cleared land (23–25), but others posit that agriculture is expanding into rainforests (22, 26–28). This debate became even more pressing with the surge in the demand for biofuel, because recent studies have argued that expansion of biofuel crops into rainforests may substantially increase rather than decrease net carbon emissions (29–31).
Most studies have focused on net expansion in agricultural area, and those that identify land sources often are limited to local and regional scales. For example, Morton et al. (21) tracked the origins of expanding soybean fields in Brazil using a combination of remote sensing and field verification in the state of Mato Grosso along the Amazon basin’s agricultural frontier. Similarly, Brown et al. (23) examined soy expansion in a portion of Rondônia, Brazil. Brink and Eva (32) used a sample of Landsat imagery to quantify land-cover dynamics across sub-Saharan Africa between 1975 and 2000. Others have postulated land sources from the United Nations Food and Agricultural Organization’s (FAO) national-level agriculture and forestry statistics for broad regions (22, 30), but these data are highly aggregated, have been described as unreliable (33), and do not provide the spatially detailed information needed for an accurate identification of land sources for new agricultural landscapes.
Xem thêm: Review Sữa Rửa Mặt 3W Trà Xanh, Review Sữa Rửa Mặt 3W Clinic Trà Xanh
To describe the pathways of agricultural expansion across the tropics systematically, we analyzed a library of satellite-based, high-resolution land-cover maps and change statistics for the 1980s and 1990s also compiled by the FAO (Fig. 1). This remotely sensed database is distinct from the FAO country statistics and offers dramatic improvements over other information sources.
Bình luận