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Bird Watching in the Forest Riparian
“Teacher! Teacher! Teacher!” came the shrill cry from the woods.
“The birds talk to me,” said Anna Peterson with a big grin. “That’s an Ovenbird. Oh! And do you hear the squeaky wheel? That’s a black and white warbler. Cool!”
Her enthusiasm was catching for the audience of about 10 forest professionals, who gathered around her to learn about breeding birds’ response to forest harvesting in tree buffer zones near streams. Peterson is a University of Minnesota biology doctorate candidate finishing up a long-term NRRI research project on birds in forest riparian zones.
Loggers leave a buffer of trees near streams to protect the water quality, but sometimes those buffers hold valuable timber. NRRI wants to find out if harvesting of some trees can take place in those riparian zones without degrading water quality or negatively impacting wildlife. NRRI has been taking part in an 11-year-study on Pokegama Creek near Grand Rapids to understand the effect of two harvesting methods on bird populations—especially those considered “priority” species.
Two harvesting techniques are being studied: tree length cuts where the whole tree is taken from the site, branches and all, and cut-to-length harvesting where the branches are cut off at the site and only the log is taken.
What they’ve learned is that any harvesting of trees affects the bird community for as much as nine years after the harvest when the more particular birds start moving back into the harvested riparian zones.
“After a harvest, birds that migrate long distances come back to find their nests sites but if they’re gone they move on,” said Peterson. “But some birds do very well in early successional forests, like the Chestnut-sided Warbler.”
A separate but similar study at eight sites in northern Minnesota is also underway with funding from the Legislative-Citizen Commission on Minnesota’s Resources (LCCMR). This study began in 2001 to understand the effects of new riparian zone guidelines that allow some harvesting of timber in these buffer zones.
In particular, the study focused on how differences in tree density (residual basal area) would affect populations of birds. By harvesting riparian zones at different tree densities they could determine which bird species were associated with the different basal areas. They learned that with increasing tree densities, short-distance migrant species (like the American Robin) decreased and birds that prefer early successional forests like Mourning Warblers also decreased.
The May workshop, “At Water’s Edge: Current state of riparian
forest management research in Minnesota” was well attended by over
100 natural resources professionals and loggers over the course of three
days. UPM/Kymmene paper company allowed researchers the use of 144 acres
for the Pokagama Creek studies. The company’s foresters took part
in the workshop to continue to improve their management strategies.
Posted Aug 8, 2008
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