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Stri Laurance Chapter 4 2010.Pdf CHAPTER 4 Habitat destruction: death by a thousand cuts William F. Laurance Humankind has dramatically transformed much 4.1 Habitat loss and fragmentation of the Earth’s surface and its natural ecosystems. Habitat destruction occurs when a natural habitat, This process is not new—it has been ongoing for such as a forest or wetland, is altered so dramati- millennia—but it has accelerated sharply over the cally that it no longer supports the species it origi- last two centuries, and especially in the last sev- nally sustained. Plant and animal populations are eral decades. destroyed or displaced, leading to a loss of biodi- Today, the loss and degradation of natural ha- versity (see Chapter 10). Habitat destruction is bitats can be likened to a war of attrition. Many considered the most important driver of species natural ecosystems are being progressively razed, extinction worldwide (Pimm and Raven 2000). bulldozed, and felled by axes or chainsaws, until Few habitats are destroyed entirely. Very often, only small scraps of their original extent survive. habitats are reduced in extent and simultaneously Forests have been hit especially hard: the global fragmented, leaving small pieces of original habi- area of forests has been reduced by roughly half tat persisting like islands in a sea of degraded over the past three centuries. Twenty-five nations land. In concert with habitat loss, habitat frag- have lost virtually all of their forest cover, and mentation is a grave threat to species survival another 29 more than nine-tenths of their forest (Laurance 2002; Sekercioglu 2002; (MEA 2005). Tropical forests are disappearing et al. et al. Chapter 5). at up to 130 000 km2 a year (Figure 4.1)—roughly Globally, agriculture is the biggest cause of hab- 50 football fields a minute. Other ecosystems itat destruction (Figure 4.2). Other human activ- are less imperiled, and a few are even recover- ities, such as mining, clear-cut logging, trawling, ing somewhat following past centuries of overex- and urban sprawl, also destroy or severely degrade ploitation. habitats. In developing nations, where most habi- Here I provide an overview of contemporary tat loss is now occurring, the drivers of environ- habitat loss. Other chapters in this book descr- mental change have shifted fundamentally in ibe the many additional ways that ecosystems recent decades. Instead of being caused mostly by are being threatened—by overhunting (Chapter small-scale farmers and rural residents, habitat 6), habitat fragmentation (Chapter 5), and climate loss, especially in the tropics, is now substantially change (Chapter 8), among other causes—but driven by globalization promoting intensive agri- my emphasis here is on habitat destruction culture and other industrial activities (see Box 4.1). per se. I evaluate patterns of habitat destruction geographically and draw comparisons among different biomes and ecosystems. I then consider some of the ultimate and proximate factors that 4.2 Geography of habitat loss drive habitat loss, and how they are changing Some regions of the Earth are far more affected by today. habitat destruction than others. Among the most 73 74 CONSERVATION BIOLOGY FOR ALL Figure 4.1 The aftermath of slash‐and‐burn farming in central Amazonia. Photograph by W. F. Laurance. imperiled are the so-called “biodiversity hotspots”, and degraded, are examples of biodiversity hot- which contain high species diversity, many locally spots. Despite encompassing just a small fraction endemic species (those whose entire geographic (<2%) of the Earth’s land surface, hotspots may range is confined to a small area), and which have sustain over half of the world’s terrestrial species lost at least 70% of their native vegetation (Myers (Myers et al. 2000). et al. 2000). Many hotspots are in the tropics. The Many islands have also suffered heavy habitat Atlantic forests of Brazil and rainforests of West loss. For instance, most of the original natural Africa, both of which have been severely reduced habitat has already been lost in Japan, New Figure 4.2 Extent of land area cultivated globally by the year 2000. Reprinted from MEA (2005). HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 75 Box 4.1 The changing drivers of tropical deforestation William F. Laurance Tropical forests are being lost today at an alarming pace. However, the fundamental (b)(b) drivers of tropical forest destruction have changed in recent years (Rudel 2005; Butler and Laurance 2008). Prior to the late 1980s, deforestation was generally caused by rapid human population growth in developing nations, in concert with government policies for rural development. These included agricultural loans, tax incentives, and road construction. Such initiatives, especially evident in countries such as Brazil and Indonesia, promoted large influxes of colonists into frontier areas and often caused dramatic forest loss. Box 4.1 Figure Changing drivers of deforestation: Small‐scale More recently, however, the impacts of rural cultivators (a) versus industrial road construction (b) in Gabon, peoples on tropical forests seem to be central Africa. Photograph by W. F. Laurance. stabilizing (see Box 4.1 Figure). Although At the same time, globalized financial many tropical nations still have considerable markets and a worldwide commodity boom are population growth, strong urbanization creating a highly attractive environment for trends (except in Sub‐Saharan Africa) mean the private sector. Under these conditions, that rural populations are growing more large‐scale agriculture—crops, livestock, and slowly, and are even declining in some tree plantations—by corporations and wealthy areas. The popularity of large‐scale frontier‐ landowners is increasingly emerging as the colonization programs has also waned. biggest direct cause of tropical deforestation If such trends continue, they could begin (Butler and Laurance 2008). Surging demand to alleviate some pressures on forests for grains and edible oils, driven by the global from small‐scale farming, hunting, and thirst for biofuels and rising standards of living fuel‐wood gathering (Wright and Muller‐ in developing countries, is also spurring this landau 2006). trend. In Brazilian Amazonia, for instance, large‐scale ranching has exploded in recent (a)(a) years, with the number of cattle more than tripling (from 22 to 74 million head) since 1990 (Smeraldi and May 2008), while industrial soy farming has also grown dramatically. Other industrial activities, especially logging, mining, and petroleum development, are also playing a critical but indirect role in forest destruction (Asner et al. 2006; Finer et al. 2008). These provide a key economic impetus for forest road‐building (see Box 4.1 Figure), which in turn allows influxes of colonists, hunters, and miners into frontier areas, often leading to rapid forest disruption and cycles of land speculation. continues 76 CONSERVATION BIOLOGY FOR ALL Box 4.1 (Continued) REFERENCES threats to wilderness, biodiversity, and indigenous peoples. PLoS One, doi:10.1371/journal.pone.0002932. Asner, G. P., Broadbent, E., Oliveira, P., Keller, M., Knapp, Rudel, T. K. (2005). Changing agents of deforestation: D., and Silva, J. (2006). Condition and fate of logged from state‐initiated to enterprise driven processes, forests in the Amazon. Proceedings of the National 1970–2000. Land Use Policy, 24,35–41. Academy of Sciences of the United States of America. Smeraldi, R. and May, P. H. (2008). The cattle realm: 103, 12947–12950. a new phase in the livestock colonization of Butler, R. A. and Laurance, W. F. (2008). New strategies Brazilian Amazonia. Amigos da Terra, Amazônia for conserving tropical forests. Trends in Ecology and Brasileira, São Paulo, Brazil. Evolution, 23, 469–72. Wright, S. J. and Muller‐Landau, H. C. (2006). The Finer, M., Jenkins, C., Pimm, S., Kean, B., and Rossi, C. future of tropical forest species. Biotropica, 38, (2008). Oil and gas projects in the western Amazon: 287–301. Zealand, Madagascar, the Philippines, and Java palm or rubber plantations (MacKinnon 2006; (WRI 2003). Other islands, such as Borneo, Suma- Laurance 2007; Koh and Wilcove 2008; see Box tra, and New Guinea, still retain some original 13.3). Older agricultural frontiers, such as those in habitat but are losing it at alarming rates (Curran Europe, eastern China, the Indian Subcontinent, et al. 2004; MacKinnon 2006). and eastern and midwestern North America, Most areas of high human population density often have very little native vegetation remaining have suffered heavy habitat destruction. Such (Figure 4.2). areas include much of Europe, eastern North America, South and Southeast Asia, the Middle East, West Africa, Central America, and the Ca- 4.3 Loss of biomes and ecosystems ribbean region, among others. Most of the biodi- 4.3.1 Tropical and subtropical forests versity hotspots occur in areas with high human density (Figure 4.3) and many still have rapid A second way to assess habitat loss is by contrast- population growth (Cincotta et al. 2000). Human ing major biomes or ecosystem types (Figure 4.4). populations are often densest in coastal areas, Today, tropical rainforests (also termed tropical many of which have experienced considerable moist and humid forests) are receiving the greatest losses of both terrestrial habitats and nearby attention, because they are being destroyed coral reefs. Among others, coastal zones in Asia, so rapidly and because they are the most biologi- northern South America, the Caribbean, Europe, cally diverse of all terrestrial biomes. Of the rough- and eastern North America have all suffered se- ly 16 million km2 of tropical rainforest that vere habitat loss (MEA 2005). originally existed worldwide, less than 9 million Finally, habitat destruction can occur swiftly in km2 remains today (Whitmore 1997; MEA 2005). areas with limited human densities but rapidly The current rate of rainforest loss is debated, with expanding agriculture. Large expanses of the different estimates ranging from around 60 000 2 2 Amazon, for example, are currently being cleared km (Achard et al.
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