Tropical forest cover change in the 1990s and options for future monitoring

Abstract

Despite the importance of the world's humid tropical forests, our knowledge concerning their rates of change remains limited. Two recent programmes (FAO 2000 Forest Resources Assessment and TREES II), exploiting the global imaging capabilities of Earth observing satellites, have recently been completed to provide information on the dynamics of tropical forest cover. The results from these independent studies show a high degree of conformity and provide a good understanding of trends at the pan-tropical level. In 1990 there were some 1150 million ha of tropical rain forest with the area of the humid tropics deforested annually estimated at 5.8 million ha (approximately twice the size of Belgium). A further 2.3 million ha of humid forest is apparently degraded annually through fragmentation, logging and/or fires. In the sub-humid and dry tropics, annual deforestation of tropical moist deciduous and tropical dry forests comes to 2.2 and 0.7 million ha, respectively. Southeast Asia is the region where forests are under the highest pressure with an annual change rate of -0.8 to -0.9%. The annual area deforested in Latin America is large, but the relative rate (-0.4 to -0.5%) is lower, owing to the vast area covered by the remaining Amazonian forests. The humid forests of Africa are being converted at a similar rate to those of Latin America (-0.4 to -0.5% per year). During this period, secondary forests have also been established, through re-growth on abandoned land and forest plantations, but with different ecological, biophysical and economic characteristics compared with primary forests. These trends are significant in all regions, but the extent of new forest cover has proven difficult to establish. These results, as well as the lack of more detailed knowledge, clearly demonstrate the need to improve sound scientific evidence to support policy. The two projects provide useful guidance for future monitoring efforts in the context of multilateral environmental agreements and of international aid, trade and development partnerships. Methodologically, the use of high-resolution remote sensing in representative samples has been shown to be cost-effective. Close collaboration between tropical institutions and inter-governmental organizations proved to be a fruitful arrangement in the different projects. To properly assist decision-making, monitoring and assessments should primarily be addressed at the national level, which also corresponds to the ratification level of the multilateral environmental agreements. The Forest Resources Assessment 2000 deforestation statistics from countries are consistent with the satellite-based estimates in Asia and America, but are significantly different in Africa, highlighting the particular need for long-term capacity-building activities in this continent.

Tree Diversity Changes over a Decade (2003-2013) in Four Inland Tropical Dry Evergreen Forest Sites on the Coromandel Coast of India

“…Tropical forests cover just ten per cent of the earth's surface but contain more than 50% of plant species (Mayaux et al 2005). They act as reservoirs of biodiversity, timber, medicinal plants, and oxygen, and play a critical role in watershed protection (Richards 1996).…”

The 2010 challenge: data availability, information needs and extraterrestrial insights

“…There is considerable scope for the development and wider implementation of improved methods (Buckland et al 2005) for post-stratification, and the calculation of indicators, but indicators that depend upon incomplete existing data collected for other purposes will always be weakened by the impossibility of excluding all potential sources of bias. In other cases, data are either complete (the Red List Index of Butchart et al 2005), or made up of a carefully chosen sample (Gregory et al 2005;Mayaux et al 2005; and the scheme proposed by Nic Lugadha et al 2005). However, even in these cases, it is important to assess critically the wider representativeness of the data (e.g.…”

“…Yet biodiversity, ecosystem services, and their erosion affect everyone, and broader involvement in the issues underpinning biodiversity policy is thus essential to efforts to manage it more sustainably. Routes to widening involvement include the increased use of local calibration and ground truthing of remotely sensed data (Mayaux et al 2005), the development of volunteer networks for data gathering (Bennun et al in press;Roberts et al in press;Thomas et al 2005), and the exploration of ways in which locally collected data (e.g. on the delivery of ecosystem services) can feed up into higher-level metaanalyses (see Bennun et al in press; Danielsen et al in press; Roberts et al in press).…”

Environmental changes during secondary succession in a tropical dry forest in Mexico

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