Major extinction of tropic forest organisms predicted

If the predictions contained in an article released yesterday in Conservation Letters (in pre-print form on June 22), are correct, the Anthropocene period is likely to begin with a mass extinction of a magnitude similar to the five major extinction events that have taken place in Earth’s history. We’ve seen how mass dying is currently taking place in the ocean. Now Gregory P. Asner (of the Carnegie Institution’s Department of Global Ecology in Stamford, California) and fellow authors report in “Combined effects of climate and land-use change on the future of humid tropical forests” that from 60 to over 80% of the species in tropical forests are likely to become extinct in less than 100 years. Given that over half of terrestrial plant and animal species current live in such forests, this projection rivals what took place during the late Triassic extinction event.

The main culprits are global warming (of course) and uncontrolled logging and deforestration. The authors conclude that the negative impact on biodiversity in the tropical forests will be negative regardless of what model is used to predict precipitation change. This is so because: (1) organisms in tropical environments have a narrower tolerance for temperature change than do temperate species; (2) tropical species are not rapid dispersers and the territorial they need to cover to find equivalent temperatures is great; and (3) the drying of the environment due to increased transpiration caused by temperature increases will cause environmental destruction.

Factoring in projected land usages from logging and other deforestation processes the authors predict that “only about 20%of the biome will likely remain beyond the footprints of these reorganizing forces.” The impacts will be different in each of the major geographical areas. They estimate the impacts in the three major forests as follows:

“In the Amazon, a combination ofclimate change and land use renders up to 81% of the region susceptible torapid vegetation change. In the Congo, logging and climate change could negatively affect the biodiversity in 35–74% of the basin. Climate-driven changes may play a smaller role in Asia-Oceania compared to that of Latin America or Africa, but land use renders 60–77% of Asia-Oceania susceptible to major biodiversity changes.”

The destruction of these forests by human activity, directly by deforestation and indirectly by greenhouse gas emission, represents, the authors understate “one of the greatest global change experiments on Earth today.” It is hard to imagine any beneficial results from this experiment, however.

Asner is quoted in the Carnegie Institution for Science press release on the study as offering the following recommendations:

“For those areas of the globe projected to suffer most from climate change, land managers could focus their efforts on reducing the pressure from deforestation, thereby helping species adjust to climate change, or enhancing their ability to move in time to keep pace with it. On the flip side, regions of the world where deforestation is projected to have fewer effects from climate change could be targeted for restoration.”

The same press release quotes Daniel Nepstad, senior scientist at the Woods Hole Research Center, as saying: “Conservation of the world’s biota, as we know it, will depend upon rapid, steep declines in greenhouse gas emissions.” Given our experience in the past two years (which began with great expectations of helpful change), we probably should be considering how to adjust (if at all) to a world depleted of a vast number of its species.

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