Grazing animals important factor in predicting global warming impact
Environmental News Network,
The impact of global warming in the
The team's results will be published in the online Early Edition of the journal Proceedings of the National Academy of Sciences.
Most computer models indicate that shrubs will thrive and spread as a result of global warming. And because shrubs have an increased ability over grasses and other small plants to absorb the greenhouse gas carbon dioxide, many scientists believe that shrubs will absorb some of this carbon dioxide and, thereby, lessen the impact of climate change. While Post and Pederson agree that global warming will promote the growth of shrubs, they argue that grazing by muskoxen and caribou will reduce the carbon-mitigating benefit of the plants.
"If you imagine a chessboard on which the dark squares are shrubs and the light squares are grasses, warming alone would tend to increase the size of the dark squares until the chess board is completely filled in," said Post. "Our experiment suggests that herbivores, like caribou and muskoxen, will slow this process, inhibit it, or perhaps even increase the size of the white squares on the chessboard."
The researchers conducted a novel five-year experiment in
Post and Pederson found that muskoxen graze more heavily in certain areas than caribou, perhaps due to their sedentary nature.
To document the effects of warming alone on vegetation, the scientists constructed fences around several plots to exclude muskoxen and caribou. They found that warming did, indeed, promote the growth of shrubs, but they also found that, in the warmed plots outside the fences, muskoxen and caribou reduced this growth by 19 percent. In particular, the animals reduced the growth of dwarf birch by 46 percent and willow by 11 percent.
Post's research also revealed that muskoxen -- rather than the more numerous caribou -- were responsible for most of the grazing. "This discovery is quite surprising, considering that muskoxen occur at such a low density at our site," said Post, who added that the result may be due to the sedentary nature of Muskoxen which, in contrast to caribou, tend to graze in one location for long periods of time. Muskoxen at Post's site also occur at lower densities than they do elsewhere in
"Careful management and conservation of existing populations of muskoxen and caribou, as well as other large herbivores, should be a priority in plans to mitigate the effects of climate change on ecosystems," said Post. "Until now, these animals seem to have been regarded more as background noise than as an active component of the ecosystem's response to warming."
In addition to the impact of muskoxen and caribou, Post and Pederson also measured the impact of an unexpected moth outbreak on vegetation in their plots. They found that by munching on the leaves and stems of plants, the moths contributed significantly to the reduction of live plant tissues.
"Our results suggest that herbivores in the
This research was supported, in part, by grants from the Committee for Research and Exploration of the National Geographic Society and the National Science Foundation.
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