A second way to assess habitat loss is by contrastingmajor biomes or ecosystem types. Today, tropical rainforests (also termed tropical moist and humid forests) are receiving the greatest attention, because they are being destroyed so rapidly and because they are the most biologically diverse of all terrestrial biomes. Of the roughly 16 million km2 of tropical rainforest that originally existed worldwide, less than 9 million km2 remains today (Whitmore 1997; MEA 2005). The current rate of rainforest loss is debated, with different estimates ranging from around 60 000 km2 (Achard et al. 2002) to 130 000 km2 per year (FAO 2000). Regardless of which estimate one adheres to, rates of rainforest loss are alarmingly high. Rates of rainforest destruction vary considerably among geographic regions. Of the world’s three major tropical regions, Southeast Asian forests are disappearing most rapidly in relative terms , while the African and New World tropics have somewhat lower rates of percent- annual forest loss (Sodhi et al. 2004). Such averages, however, disguise important smaller scale variation.
In the New World tropics, for example, the Caribbean, Meso American, and Andean regions are all suffering severe rainforest loss, but the relative deforestation rate for the region as a whole is buffered by the vastness of the Amazon. Likewise, in tropical Africa, forest loss is severe in West Africa, montane areas of East Africa, and Madagascar, but substantial forest still survives in the Congo Basin (Laurance 1999). Other tropical and subtropical biomes have suffered even more heavily than rainforests. Tropical dry forests (also known as monsoonal or deciduous forests) have been severely reduced, in part because they are easier to clear and burn than rainforests. For instance, along Central America’s Pacific coast, much less than 1% of the original dry forest survives. Losses of dry forest have been nearly as severe in Madagascar and parts of Southeast Asia (Laurance 1999; Mayaux et al. 2005).
Mangrove forests, salt-tolerant ecosystems that grow in tropical and subtropical intertidal zones, have also been seriously reduced. Based on countries for which data exist, more than a third of all mangroves were lost in the last few decades of the 20th century (MEA 2005). From 1990 to 2000, over 1% of all mangrove forests were lost annually, with rates of loss especially high in Southeast Asia (Mayaux et al. 2005). Such losses are alarming given the high primary productivity of mangroves, their key role as spawning and rearing areas for economically important fish and shrimp species, and their importance for sheltering coastal areas from destructive storms and tsunamis (Danielsen et al. 2005).
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