Common tree species in the Amazon will survive even grim scenarios of deforestation and road-building, but rare trees could suffer extinction rates of up to 50 percent, predict Smithsonian scientists and colleagues in the Aug. 12 issue of the journal Proceedings of the National Academy of Science.
How resilient will natural systems prove to be as they weather the next several decades of severe, human-induced global change? The debate is on between proponents of models that maximize and minimize extinction rates.
The Amazon basin contains about 40 percent of the world's remaining rainforest. One of the fundamental characteristics of tropical forests is the presence of very rare tree species. Competing models of relative species abundance, one based on Fisher's alpha statistic and the other based on Preston's lognormal curve, yield different proportions of rare trees in the forest.
It isn't clear how much of the expected extinction they expect will come from climate change versus logging and conversion of forests to pasture and farm land.
A few thousand tree species might be lost.
In this offering, the authors use the neutral theory to predict the number of tree species and to test predictions of the Millenium Ecosystems Assessment that forecasts major tree extinctions in the Amazon over the next several decades. First, they estimate that the Brazilian Amazon has (or had) 11,210 large tree species, and, of these, 5,308 species are classified as rare.
Based on optimistic and non-optimistic scenarios for road construction in the Amazon published by the Smithsonian's William Laurance and colleagues in the journal Science in 2004, they predict that the rare species will suffer between 37 and 50 percent extinction, whereas the extinction rate for all trees could be from 20 to 33 percent overall.
How much rain forest will survive the growth in demand for trees, livestock grazing land, and farm land for food and biomass energy crops? Economic development, population growth, and depletion of oil and natural gas fields each create pressures to convert more and more wild lands into industrial uses. Jungles look to become rare.
|Share |||Randall Parker, 2008 August 18 09:46 PM Trends Extinction|