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 report in a March issue of the journal Science
is the first systematic look at how biodiversity is likely to
be impacted by several agents of human-caused global change and
global warming and climate change aren't necessarily the principal
factors.
 In the
article, researchers look at what factors affect biodiversity,
what kinds of habitats are susceptible to those factors and what
may happen to biodiversity between now and 2100. The article's
19 authors, from the United States, Latin America, Europe and
Australia, include two Colorado State University faculty members,
Diana Wall, director of Colorado State's Natural Resource Ecology
Laboratory, and N. LeRoy Poff, assistant professor of biology.
Global warming
and climate change aren't necessarily the principal factors in
the loss of biodiversity anticipated over the next century, Poff
said. Nitrogen deposition and particularly land-use change and
the introduction of nonnative species can play a significant
role in some ecosystems. "For most ecological systems, land-use
change is more important than climate change within the next
50-100 years," said Poff, a specialist in freshwater ecosystems.
"If climate change were to just go away tomorrow, land-use
change will still drive down biodiversity.
"We have
to think about ways to reduce land-use change and biotic introductions
in order not to exacerbate what happens when climate change is
thrown into the mix."
The researchers
identified five primary influences, or "drivers," in
global change that in turn affect biodiversity: global atmospheric
carbon dioxide, climate change, biotic change (the introduction
of new species to an ecosystem), nitrogen deposition and land-use
change (for example, development, and agricultural and forestry
practices). They then identified 10 terrestrial biological communities,
called "biomes," and tried to assess how sensitive
each was to a particular driver. The biomes included alpine,
arctic, boreal forest, deserts, grasslands, Mediterranean systems,
Northern temperate forest, savanna, Southern temperate forest
and tropical forests. The researchers also examined freshwater
ecosystems, both lakes and running water, and soil.
Poff said
biotic exchange is a much greater threat to freshwater systems,
particularly lakes, than to terrestrial biomes. Aquatic species
have typically evolved in relatively isolated habitats, and introduction
of a new species often produces stress on the food chain or some
other aspect of native species' existence. Freshwater ecosystems
are very sensitive to poor land-use practices, Poff said, because
as low points on the landscape, they accumulate damaging silt
and excess nutrients from runoff.
The earth's
surface wasn't the only focus of the study. Wall, a professor
of rangeland ecosystems and a specialist in soil biodiversity
and microscopic invertebrates, said below-ground species, from
bacteria to worms, currently are most harshly effected by land-use
change.
"That's
because soil is usually torn up," she said. "It's taken
perhaps a hundred years to form an inch of soil, and whether
we're digging a ditch or cultivating a garden, we're disturbing
that ecosystem, the habitat for thousands of species."
Of the global
change drivers, carbon dioxide levels are probably the hardest
to assess in terms of their direct influence on soil biodiversity,
Wall said. Nonetheless, the indirect effects through plants of
increased carbon dioxide concentrations may be significant, she
said.
On land, the
researchers found, Mediterranean-climate and grassland ecosystems
will probably experience the greatest proportional change in
biodiversity because all five factors affect them. Northern temperate
ecosystems will likely experience the least biodiversity change,
primarily because they've already been so extensively affected
by major land-use change. The most land-use change will occur
in tropical forests and the temperate forests of South America
and the least in arctic and alpine biomes.
Climate change
will affect high latitudes the most. It will produce the fewest
changes in the tropics and have intermediate effects in other
biomes. Nitrogen deposition is greatest near northern cities
in temperate zones and least in the arctic and southern temperate
forests. Overall, land-use change seems to be the dominant driver,
although in some biomes land-use and climate change have relatively
little effect. In freshwater systems, land-use change has the
most effect on rivers, while biotic exchange has the most affect
on lakes. However, Poff said, this knowledge suggests directions
biodiversity is to be preserved to the greatest extent possible.
"The
hopeful message from this is that if we care about biodiversity,
we can examine land-use, help mitigate climate change and save
species," he said. 
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