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Diversity is a double-edged sword

作者:贾壕胱    发布时间:2019-02-28 10:15:08    

By Jeff Hecht ECOLOGISTS may have missed out on a whole level of biological diversity in the Amazon rainforest, warn researchers in Finland and Peru. This can only complicate the task of conserving tropical biodiversity. Many previous studies have found huge local diversity in patches of Amazon forest. One survey counted some 400 tree species in a single hectare. But researchers have assumed that biodiversity does not vary strongly on a local scale, from hectare to hectare. Now Hanna Tuomisto and her colleagues at the University of Turku in Finland, working with researchers at the National Institute of Natural Resources in Lima, Peru, say that there are more than a hundred distinct vegetation types in the half-million square kilometres of the Amazon lowlands in Peru. Each of these “biotopes” may contain a different range of plant species, the researchers say. Tuomisto’s group analysed images taken by the Landsat series of satellites. These showed distinct patterns which the researchers took to indicate variation in the structure of the forest and the species present. From the satellite images, they were able to identify more than a hundred different forest biotopes. They then went out into the forest to examine some of these sites, and confirmed that the patterns recorded on the satellite images corresponded to differences in vegetation. For example, some sites had a complete forest canopy, while in others the canopy was broken, and shorter species such as bamboo were abundant. “We have actually visited about twenty biotopes and know that they are pretty strikingly different,” says Tuomisto. Finally, the researchers counted the numbers of species of fern and a group of tropical flowering plants called the Melastomataceae along transects through several distinctive biotopes. These surveys revealed that the biological diversity of the biotopes varied greatly. At one site, for instance, a 400-metre transect contained some sixty species, whereas a similar transect in the least diverse biotope contained fewer than half this number (Science, vol 269, p 63). Tuomisto believes that the patterns observed on the satellite images are caused by differences in soil type. Variations in climate, she says, operate on a much larger scale, while differences in drainage typically affect smaller areas. Whatever the cause, the existence of many distinctive forest biotopes adds to the difficulty of preserving rainforest diversity. “If we want to conserve, we should make sure samples of all the biotopes are included in the conservation programme,” says Tuomisto. The researchers are cautious about generalising their results to the whole of the Amazon rainforest, as their study covered only about 10 per cent of the Amazon basin. But they are confident that the forest as a whole contains many more biotopes than have been identified so far. Tuomisto says that a concerted effort is now needed to document the biotopes present across the entire Amazon basin. Without help, she says,

 

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