1999


From: Ecological Society of America

Survival Of The Yellowstone Grizzlies, Ferns As Forest Filters And The Role Of Worms In Climate Change: The April Edition Of Ecology Is Now Available

The latest edition of Ecology is now available. The journal includes studies on a wide variety of topics, including:

Demography of the Yellowstone Grizzly Bears
Yellowstone's grizzly bears (Ursus arctos) may seem awesomely powerful to National Park visitors, but a new study suggests they are still very threatened as a species. Written by Craig Pease (Vermont Law School) and David Mattson (US Geological Survey, Biological Resources Division), the paper analyzed nearly two decades of data on radio-collared bears in the Yellowstone ecosystem. The researchers concluded that the number of bears has changed little in the past two decades, despite intensive grizzly bear management. Bear mortality is nearly double in years when the whitebark pine crop fails, and the whitebark pine itself is in trouble, say the authors. The pine crop is now failing almost every other year, and widespread suppression of fires has also been detrimental to its health. Global warming may also pose a threat to the tree species. People also cause bear mortality in both direct and indirect ways, the researchers assert. Humans have directly caused 70-90% of all known grizzly bear deaths in the Yellowstone ecosystem since the 1970s. Whitebark pines are found at higher elevations that tend to be less used by humans. When the pine crop fails, the bears move to lower-elevation sites (which are closer to humans) to feed. "When the whitebark pine crop fails, the grizzly bear is hit with a double whammy," says Pease. "Simply being around more people increases their immediate chance of death. And by foraging closer to humans, grizzlies lose their natural wariness of people. Those bears will then have an increased risk of death forever, even in years with abundant pine seeds."

The Fern Understory as an Ecological Filter
They are seedless, flowerless and relatively small in stature, but a new study suggests that ferns can play an important role in determining the future composition of forests. Lisa George and F.A. Bazzaz of Harvard University examined how the growth rates of several kinds of trees were affected by the presence of a fern understory. Working for three years in the Harvard Forest of Massachusetts, the researchers compared the survival rates of red maples (Acer rubrum), yellow birches (Betula alleghaniensis) and red oaks (Quercus rubra) in fern covered areas to the survival rates of these same kinds of trees in fern-free areas. They discovered that hayscented ferns (Dennstaedtia punctilobula) and interrupted ferns (Osmunda claytonia) affected the growth and survival rates of seedlings for all of the species, but the magnitude of the effect differed among the various kinds of trees. All of the seedlings grew more slowly in fern covered areas. But, say the researchers, the ultimate survival of the oak seedlings did not differ between fern and fern-free areas. By contrast, the birch seedlings were highly affected, with only one third of the birches under the ferns surviving after two years. Shade provided by the fern fronds was the main determining factor in the growth patterns of the trees in the study. "The fern understory is a powerful filter," says George. "Fern presence in a forest can determine the size, the species, and the density of the trees."

Earthworms Shed Light on Plant Responses to Climate Change
Earthworms first achieved celebrity status when their role in food compost and soil health was discovered. Surprisingly enough, scientists now believe that the next claim to fame for these little subterranean creatures is in their fecal droppings. Johann Zaller and John Arnone at the Universitaet Basel in Switzerland (now at Utah State University and the Desert Research Institute in Reno, Nevada, respectively) conducted studies investigating plant responses to climate change in grassland ecosystems. Their work has demonstrated a unique relationship between plant growth and earthworm castings under different levels of CO2. The rich earthworm castings, which are more abundant in nutrients than surrounding soils, are valuable resources for plants. Zaller and Arnone discovered that plant species that grew in closer association with worm excrement displayed more growth under higher levels of CO2 than non-associated species. According to Zaller and Arnone, "Worm castings have a significant impact on the community structure of grasslands and will continue to influence their future structure as global CO2 levels continue to rise."

Ecology is a peer-reviewed journal published eight times a year by the Ecological Society of America (ESA). Copies of the above article are available free of charge to the press through the Society's Public Affairs Office. Members of the press may also obtain copies of ESA's entire family of publications, which includes Ecology, Ecological Applications, Ecological Monographs, and Conservation Ecology. Others interested in copies of articles should contact the Reprint Department at the address in the masthead.

Founded in 1915, the Ecological Society of America (ESA) is a scientific, non-profit, organization with over 7000 members. Through ESA reports, journals, membership research, and expert testimony to Congress, ESA seeks to promote the responsible application of ecological data and principles to the solution of environmental problems. For more information about the Society and its activities, access ESA's web site at: http://esa.sdsc.edu.




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