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Reply From W.F. Laurance

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Environmental Science: How green are biofuels?

Smithsonian Libraries
Global warming and escalating petroleum costs are creating an urgent need to find ecologically friendly fuels. Biofuels-such as ethanol from corn (maize) and sugarcane-have been increasingly heralded as a possible savior (1, 2). But others have argued that biofuels will consume vast swaths of farmland and native habitats, drive up food prices, and result in little reduction in greenhouse-gas emissions (3-5). An innovative study by Zah et al. (6), commissioned by the Swiss government, could help to resolve this debate by providing a detailed assessment of the environmental costs and benefits of different transport biofuels.

Scale-dependent patterns of deforestation in the Brazilian Amazon

Smithsonian Libraries
Tropical forests of the Amazon Basin are being rapidly converted to agricultural land uses and fallow land, resulting in accelerating rates of forest loss in one of the world's most biodiverse ecoregions. This process has been extensively described andmodelled, but as yet there has been no formal test ofhowthe spatial patterns of deforested and fragmented areas change with the spatial scale of forest clearings. It was hypothesised that different land-use practices are driving small and large clearings, with small-scale cultivators often creating small, irregularly shaped clearings and largescale ranchers and soy farmers creating larger, more regular-shaped clearings. To quantitatively test this hypothesis,Mandelbrot's theory of fractalswas applied to deforested areas in the Brazilian Amazon to test for scale-invariance in deforestation patterns. The spatial pattern of deforestation differed between small and large clearings,with the former creating more complex landscapes and with a threshold occurring at c. 1200 ha in area. As a consequence, the sizes and shapes of forest clearings, and hence the relative vulnerability of the remaining forest to edge, area and isolation effects, may differ systematically between landscapes with different deforestation drivers. Further tests of this hypothesis are needed to assess its efficacy in other tropical landscapes and geographical locations.

Impacts of roads and linear clearings on tropical forests

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Linear infrastructure such as roads, highways, power lines and gas lines are omnipresent features of human activity and are rapidly expanding in the tropics. Tropical species are especially vulnerable to such infrastructure because they include many ecological specialists that avoid even narrow (<30-m wide) clearings and forest edges, as well as other species that are susceptible to road kill, predation or hunting by humans near roads. In addition, roads have a major role in opening up forested tropical regions to destructive colonization and exploitation. Here, we synthesize existing research on the impacts of roads and other linear clearings on tropical rainforests, and assert that such impacts are often qualitatively and quantitatively different in tropical forests than in other ecosystems. We also highlight practical measures to reduce the negative impacts of roads and other linear infrastructure on tropical species.

Unanticipated Effects of Stand Dynamism on Amazonian Tree Diversity

Smithsonian Libraries
We assessed a general hypothesis of tropical tree diversity that predicts that species richness will be positively correlated with stand dynamism. Our analysis was based one of the largest and longest-running datasets on Amazonian trees (226510 cm diameter at breast height), with data collected over a 23-yr period within 66 1 ha plots spanning a large (1000 km2) landscape. Within these plots, maximum tree-species richness (329 species/ha) and Fisher's 03B1 values (227.5) were among the highest ever recorded. Contrary to the diversity-dynamism concept, tree species richness in our landscape was significantly and negatively associated with stand dynamism (measured as the mean rate of annual tree turnover). Because of this unexpected finding, we critically re-evaluated the relationship between stand dynamism and tree diversity across the Amazon basin and the tropics as a whole. With the inclusion of additional data we found that the relationship between stand dynamism and tree diversity becomes non-significant at larger spatial scales. Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp

Environmental Synergisms and Extinctions of Tropical Species

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Environmental synergisms may pose the greatest threat to tropical biodiversity. Using recently updated data sets from the International Union for Conservation of Nature (IUCN) Red List, we evaluated the incidence of perceived threats to all known mammal, bird, and amphibian species in tropical forests. Vulnerable, endangered, and extinct species were collectively far more likely to be imperiled by combinations of threats than expected by chance. Among 45 possible pairwise combinations of 10 different threats, 69%, 93%, and 71% were significantly more frequent than expected for threatened mammals, birds, and amphibians, respectively, even with a stringent Bonferroni-corrected probability value (p= 0.003). Based on this analysis, we identified five key environmental synergisms in the tropics and speculate on the existence of others. The most important involve interactions between habitat loss or alteration (from agriculture, urban sprawl, infrastructure, or logging) and other anthropogenic disturbances such as hunting, fire, exotic-species invasions, or pollution. Climatic change and emerging pathogens also can interact with other threats. We assert that environmental synergisms are more likely the norm than the exception for threatened species and ecosystems, can vary markedly in nature among geographic regions and taxa, and may be exceedingly difficult to predict in terms of their ultimate impacts. The perils posed by environmental synergisms highlight the need for a precautionary approach to tropical biodiversity conservation. Los sinergismos ambientales pueden constituir la mayor amenaza para la biodiversidad tropical. Utilizando conjuntos de datos de la Lista Roja de la Unión Internacional para la Conservación de la Naturaleza (IUCN) actualizados recientemente, evaluamos la incidencia de amenazas percibidas para todas las especies conocidas de mamíferos, aves y anfibios de bosques tropicales. Las especies vulnerables, en peligro y extintas colectivamente fueron más afectadas por combinaciones de amenazas que lo esperado al azar. Entre las 45 combinaciones pareadas posibles de 10 amenazas diferentes, 69%, 83% y 71% fueron significativamente más frecuentes que lo esperado para especies amenazadas de mamíferos, aves y anfibios, respectivamente, aun con un valor de probabilidad con corrección Bonferoni (p= 0.003).Con base en este análisis, identificamos cinco sinergismos ambientales clave en los trópicos y especulamos con la existencia de otros. Las más importantes involucran interacciones entre la pérdida o alteración de hábitat (por agricultura, expansión urbana, infraestructura o explotación de madera) y otras perturbaciones antropogénicas como la cacería, el fuego, invasiones de especies exóticas o contaminación. El cambio climático y los patógenos emergentes también pueden interactuar con otras amenazas. Afirmamos que los sinergismos ambientales son más la norma que la excepción para especies y ecosistemas amenazados, que pueden variar notablemente entre regiones geográficas y taxa, y que pueden ser extremadamente difíciles de predecir en términos de sus impactos finales. Los peligros que representan los sinergismos ambientales resaltan la necesidad de un enfoque precautorio para la conservación de la biodiversidad tropical.

Deforestation in Amazonia

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Changing Drivers of Deforestation and New Opportunities for Conservation

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Over the past 50 years, human agents of deforestation have changed in ways that have potentially important implications for conservation efforts. We characterized these changes through a meta-analysis of case studies of land-cover change in the tropics. From the 1960s to the 1980s, small-scale farmers, with state assistance, deforested large areas of tropical forest in Southeast Asia and Latin America. As globalization and urbanization increased during the 1980s, the agents of deforestation changed in two important parts of the tropical biome, the lowland rainforests in Brazil and Indonesia. Well-capitalized ranchers, farmers, and loggers producing for consumers in distant markets became more prominent in these places and this globalization weakened the historically strong relationship between local population growth and forest cover. At the same time, forests have begun to regrow in some tropical uplands. These changing circumstances, we believe, suggest two new and differing strategies for biodiversity conservation in the tropics, one focused on conserving uplands and the other on promoting environmental stewardship in lowlands and other areas conducive to industrial agriculture. Los agentes humanos de la deforestación han cambiado en los últimos 50 años de manera que tienen implicaciones potencialmente importantes para los esfuerzos de conservación. Caracterizamos estos cambios mediante un meta-análisis de estudios de caso de cobertura de suelo en los trópicos. De la década de 1960 a la de 1980, campesinos de pequeña escala, con asistencia del estado, deforestaron grandes extensiones de bosque tropical en el sureste de Asia y en América Latina. A medida que la globalización y la urbanización incrementaron en la década de 1980, los agentes de la deforestación cambiaron en dos partes importantes del bioma tropical, los bosques lluviosos en tierras bajas de Brasil e Indonesia. En estos lugares se volvieron más prominentes los granjeros, agricultores y madereros bien capitalizados y esta globalización debilitó la relación históricamente estrecha entre el crecimiento de la población local y la cobertura forestal. Al mismo tiempo, los bosques han comenzado a recuperarse en algunas montañas tropicales. Creemos que estas circunstancias cambiantes sugieren dos estrategias nuevas y diferentes para la conservación de la biodiversidad en los trópicos, una enfocada a la conservación de terrenos montañosos y la otra enfocada a promover la gestión ambiental en tierras bajas y otras tierras favorables para la agricultura industrial.
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