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Long-term forest study shows birds' response to logging more complex than expected

Thursday, August 7, 2003

EMINENCE -- Ground skinks and fence lizards don't seem to suffer from timber harvests. Wood thrushes like clearcuts. Ovenbirds don't. And Kentucky warblers thrive in timber harvest areas, regardless of whether all or some of the trees are removed.

Those are some of the early trends seen in data coming out of the Missouri Ozarks Forest Ecosystem Project (MOFEP). The study aims to learn how existing forest management practices affect the forests from the smallest scale to entire landscapes.

The Missouri Department of Conservation began MOFEP as an effort to determine how active forest management was affecting birds that spend summers in Missouri and winters in Central and South America. Seeing the potential for greater understanding of a wide array of ecological issues, the Conservation Department added other facets to the long-term study.

The augmented study tracks changes in amphibians, reptiles, small mammals, forest-floor insects, bugs in the forest canopy, soils, microclimatic conditions, trees, herbaceous plants, even lichens. More information about MOFEP is available online at http://mofep.conservation.state.mo.us/ov....

MOFEP is remarkable not only for its material scope but also for its temporal span. The life of a forest far exceeds human life spans, so to understand how human activity affects the forest mechanism, it's necessary to transcend a short-term outlook. The study is designed to provide a series of snapshots of a dynamic system over the course of 100 to 150 years, making it one of the few true long-term forest ecology studies in the world.

MOFEP is being conducted on nine tracts of Conservation Department land comprising 9,000 acres. The study began in 1991, with field workers gathering baseline data. They counted plants and animals and measured physical characteristics of the nine 1,000-acre compartments to provide a basis for comparison as the study progresses.

The next phase of the study began in 1996. On three compartments, loggers harvested all the trees from areas as large as 20 acres. These clearcuts comprise one-10th of each compartment's total acreage. This process will be repeated on another 10 percent of each of the three compartments' acreage once every 15 years.

When the study reaches its conclusion, all the land in three compartments will have been clear-cut once. By then, these compartments will be mosaics of small tracts where the forest ranges from 150 years old to clear-cuts just beginning to regrow. This type of forest management is sometimes called clearcutting.

Another three MOFEP compartments will have harvests, also at 15-year intervals. However, trees will be harvested individually or in small groups so some trees always remain standing in logged areas.

The remaining three compartments won't be cut at all. They will provide a control area for comparison to the harvested tracts, allowing a fuller understanding of how the number and type of plants and animals have been affected by tree cutting in other compartments.

One of the concerns that led to MOFEP was the possibility that cutting trees fragmented large forest tracts, exposing birds to danger from predators and "nest parasitism" by cowbirds. Cowbirds lay their eggs in other birds' nests, and the larger cowbird babies crowd out the host birds' own young.

Information already is accumulating from MOFEP. For instance, while numbers of all five bird species that nest in mature forest drops sharply immediately after logging in even-age and uneven-age harvest tracts, some rebound quickly. Wood thrushes seem to find even-age harvest areas even more hospitable than those where uneven-age harvests are conducted. The opposite is true of ovenbirds and worm-eating warblers. Kentucky warblers thrived in both areas.

Another group of birds, those that nest in densely vegetated areas where trees have been removed, also showed different and sometimes surprising responses to logging. Five out of six of these "early-successional" species increased dramatically after timber harvests. Yellow-breasted chats and prairie warblers preferred even-age harvest areas, while indigo buntings and hooded warblers did equally well in even- and uneven-age tracts. But researchers found fewer blue-winged warblers and white-eyed vireos in both even- and uneven-age areas immediately after harvests, and these population decreases have continued.

Investigators speculate that the abundance of insects found in recently logged areas accounts for heavy usage by both forest-interior nesters and early-successional bird species. The dense, brushy cover in such areas also provides protection from some hawks. Overall, MOFEP results so far show no significant change in nest success rates before and after timber harvests. Similar results are coming out of amphibian, reptile and small-mammal studies.

One unanticipated result of MOFEP is the discovery of new species. Lichens are partnerships between fungi and algae. The fungi give the algae a good place to grow, and the algae make food that sustains the fungi. When documenting the types of lichen in the study area, field workers documented more than 180 species. Among those were three previously unknown to science. Another interesting discovery is that tree size doesn't seem to affect the diversity of lichen species present. The number of tree species found in a given area does.

Plant investigators are finding that the number of herbaceous plant species declines in areas where no trees are cut compared to areas with timber harvests. They also say that timber harvests in one area don't seem to affect the diversity of herbaceous plants in neighboring, unlogged areas.

The number of spotted salamanders and American toads decreased on all MOFEP areas, regardless of management, indicating something unrelated to timber harvest is hurting these species.

Conservation Department Resource Science Supervisor Eric Kurzejeski says that while these early trends are interesting, the significance of MOFEP will increase as the study progresses.

"These early results are encouraging, but some of the trends will almost certainly change as data continue to accumulate over the next 100 years," said Kurzejeski. "MOFEP will deepen our understanding of the tremendously complex relationships within trees -- which we normally think of as being the forest -- and all the other organisms and physical factors that really make up forests. This study is going to give the next generation of foresters and biologists much better information on which to base management decisions."

Funding for the ground-breaking work being done in MOFEP comes from the 1/8th percent sales tax dedicated to conservation. Missouri voters approved the tax in 1976. It provides approximately 60 percent of the Conservation Department's revenues. Although this makes Missouri's conservation agency among the best-funded in the nation, it comprises less than one-half-of 1 percent of Missouri's overall state budget.



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