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Research on wetland buffers



From the August 1997 issue of "Conservation Biology," the journal of the
Society for Conservation Biology...released August 15, 1997.
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WETLAND BUFFERS NOT PROTECTING BIODIVERSITY
 
Most policies for protecting wetlands in the U.S. and Canada include a
surrounding buffer zone of a few hundred meters at most. Buffers are
intended to protect the many species that live in or use wetlands, but
do they really work? The answer is no--current buffers are way too
small, say C. Scott Findlay and Jeff Houlahan of the University of
Ottawa in Ontario, Canada, in the August issue of Conservation Biology.
This is the first study of how big wetland buffers should be.

Previous studies by other researchers suggested that disturbances such
as building roads and clearing forests can reduce biodiversity by, for
instance, keeping animals from migrating and making it easier for
non-native species to spread. To see if disturbances on the land
adjacent to wetlands can also decrease biodiversity within the wetlands,
Findlay and Houlahan assessed the relationship between disturbances and
the diversity of mammals, birds, reptiles, amphibians and plants in 30
wetlands in southern Ontario, which has lost at least 75% of its
wetlands since Europeans settled the area in the 19th century.
 
Findlay and Houlahan found that bird diversity declined significantly
when paved roads were within a kilometer of a wetland edge; that plant
diversity declined when the roads were within a kilometer or two; and
that herptile and mammal diversity declined when roads were within two
kilometers. The researchers also found that herptile and mammal
diversity declined when forests were cleared within two kilometers of a
wetland.

Bolstering their findings, models showed that relatively small changes
in forest cover and road density could decrease biodiversity as much as
losing half the wetland itself. Specifically, when 20% of the forest is
cleared near a wetland, the diversity of reptiles, amphibians and
mammals decreases by as much as 20%. And when the density of paved roads
near a wetland increases by 20%, the diversity of plants, reptiles,
amphibians and birds decreases as much as 20%.
 
These results suggest that to preserve maximum biodiversity in wetlands,
buffers should be increased to extend a kilometer or two from wetland
edges, say Findlay and Houlahan.

Follow-up unpublished studies suggest that when a road is built near a
wetland, herptile diversity keeps decreasing for the next few decades.
"Our results suggest that our current picture of reptile and amphibian
wetland diversity--gloomy though it is--is nonetheless rosier than it
ought to be," says Findlay.
 
For more information, contact Scott Findlay, 613-562-5800 X5474 (tel),
613-562-5486 (fax), sfindlay@oreo.uottawa.ca; or Jeff Houlahan,
jeffh@sonetis.com.