This report was highlighted in today's Washington Post.  The Cedar Creek
studies, in sum, suggest that an abundance of plant species--whether native,
non-native, or both--should result in an increase in niche/resource
partitioning, and an increase in productivity and ecosystem health--i.e.,
biodiversity begets biodiversity.  Rare species are rare, historically,
because they are habitat specialists--one might ask how this happens,
without the pressure of coevolving associates?  The process of homogenizing
habitat, through human activities, has much more influence on the
composition of the resulting plant community than does the presence of alien
species. Species composition is simply a reflection of the habitat and
disturbance regime.

********************************************
Study of Plants Makes a Case for Biodiversity

By William Souder
Special to The Washington Post
Monday, April 16, 2001; Page A07

CEDAR CREEK, Minn.

Ecologists have voiced concern in recent years about the disappearance of
plants and animals around the globe. But controversy has raged over whether
Earth's diversity of species is fundamental to the stable functioning of the
planet's ecosystems.

Now, a study has produced strong evidence that biodiversity does increase
the health and productivity of an ecosystem. And, in a sneak peek at what
the world could be like in 2050, researchers have demonstrated that
preserving more species could provide a greater natural cushion against
environmental insults.

A team led by Peter B. Reich of the University of Minnesota focused on a
previously unexplored relationship between species diversity and steep
increases in nitrogen and carbon dioxide. Both are rising largely as a
result of fossil fuel consumption and chemical use by farmers. Since the
industrial revolution, carbon dioxide in the atmosphere has doubled and
continues to increase about 5 percent annually. Nitrogen, which naturally
cycles between the atmosphere and the living tissues in plants and animals,
has also doubled.

In a field experiment outwardly resembling a kind of high-tech Stonehenge,
Reich grew 16 native grasses and herbaceous plants in various combinations
inside six large circular plots at the Cedar Creek Natural History Area, a
5,000-acre oak savanna near Minneapolis. The plots are ringed with white
plastic "vent tubes" rising vertically on the perimeters. The tubes add
carbon dioxide to the air within the circles and are regulated by a computer
that adjusts for wind and other variables. Nitrogen fertilizer is also
applied to the soil to help achieve a composite approximation of the
enriched environment the researchers believe plants will grow in 50 years
from now.

As expected, all of the groups grew better with increased nitrogen and
carbon dioxide, both of which are essential to plant life. But the groupings
that included all 16 species were significantly more productive than any
combination of fewer species. More important, the most diverse plantings
outpaced the most productive single species when they were grown alone -- an
outcome called "overyielding" that plant ecologists have long considered the
elusive Holy Grail in such biodiversity experiments.

"The interpretation of similar data by critics of previous experiments has
been that a single, super species inevitably gets included in the most
diverse plots and then dominates," Reich said. "We've shown that no
individual species dominates any of our plots and that different species
combine to increase overall productivity."

Reich likened the diversity effect to the difference between a standard
basketball team and a squad made up only of lumbering centers. "The team
with an assortment of player sizes and skills will be the better one," he
said.

Plants in the most diverse groupings complement one another by using
resources in different ways and at different times, and there are also
"positive species interactions" among different plants, Reich said. These
could range from complex nutrient exchanges that are not yet well understood
to something as simple as taller plants providing needed shade for shorter
ones.

Andy Dobson, an ecologist at Princeton University, called the study "a
beautiful demonstration of the importance of biodiversity."

"This is big science," Dobson said. "We've learned more from Cedar Creek
about how our planet works that is pertinent to us than we've learned from
all the space shuttle flights put together."

Reich's work is a continuation of studies at Cedar Creek by David Tilman,
also of the University of Minnesota and a co-author of a report on the
findings in the April 12 issue of the journal Nature. Tilman's experiments
showing that diverse plant communities are more resistant to environmental
stresses such as drought have been at the center of a long-running feud
among ecologists.

Michael Huston of the Oak Ridge National Laboratory, who has been the chief
critic of the Cedar Creek work, said Reich's experiment is a big improvement
over the earlier ones. But the results really show only that a few dominant
species, primarily weeds, account for most of the productivity gains, Huston
said.

"There's clearly a diversity effect here," Huston said. "But it does not
show that you need a lot of diversity, just a few really highly productive
species."

Huston insisted that the emphasis on productivity, which is simply a measure
of the total plant mass in each grouping, is misplaced. In nature, he said,
diversity does not equal productivity.

"I'm solidly in favor of preserving biodiversity," Huston said. "I'm just
not convinced this experiment makes a strong case for it. What this says is
that if our sole aim is productivity, we should plant just a few weeds and
fertilize them."

But Reich's findings confirm what most ecologists already believe, said Joy
Zedler of the University of Wisconsin. "It's hard to think that the results
could have been any different," she said. "Diversity has to be important,
and it's manifest in this experiment."

Zedler shares the concern that several of the plants that did well in the
experiment were in fact "aggressive weeds."

"That's not surprising either," Zedler said. "It's a little scary, though."
Many ecologists see a future Earth dominated by opportunistic "weedy
species" of plants and animals that can rapidly adapt to changing
environmental conditions.

The findings also point to an intertwining of cause and effect, especially
with respect to carbon dioxide. Recent satellite data have confirmed the
role carbon dioxide plays in global warming, and other evidence links global
warming to declining biodiversity. Thus plants, which absorb nearly
one-third of all carbon dioxide emissions, are at the same time at risk from
carbon dioxide emissions.

"Nature is in effect 'scrubbing' carbon dioxide from the atmosphere for us,"
Reich said. "But we don't know if there's a saturation point, when suddenly
all of the carbon dioxide we produce will stay in the air. And now we have
learned that a less diverse biosphere will be less efficient at carbon
dioxide absorption."

Reich said that the study proves an important principle but that further
work is needed to show how it applies in natural systems. "We've tested a
basic theoretical question," he said. "The magnitude of the effect may not
be the same in nature, but I think we're likely to see a similar
relationship. And that should be a concern.

"We've gotten away with putting short-term economic considerations ahead of
future environmental well-being for a long time. And that's going to be
costly to us in the end."

© 2001 The Washington Post Company
*********************************************

Vivian Parker
Resource Policy Analyst
California Indian Basketweavers Association (CIBA)
ph  530-622-8718
fax 530-622-8748

http://www.ciba.org

Donate On-line:
http://www.helping.org/charity (search "ciba")
 
 

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