UNIVERSITY PARK, Pa. -- Some species of wildflowers that once were common in Pennsylvania are declining. Their scarcity indicates a problem, according to a Penn State forest expert.

A rich mix of native wildflowers is one indication of healthy conditions in the lower layer of the forest, known as the understory, explains Rance Harmon, a cooperative extension forest specialist. Healthy forests contain a variety of flowers, shrubs, trees and other plants, which occur in layers, from ground level to the treetops. This variety and complexity allows many different animal species to thrive and fosters environmental stability.

"But in some Pennsylvania woodlands, the lack of tree seedlings, wildflowers and other plants leaves little doubt that there is a problem," Harmon says. "Two of the culprits behind a dearth of understory growth are an overabundance of white-tailed deer and invasive plants."

Harmon notes that deer, like most humans, are selective eaters. They browse on their favorite forest plants when they are available and resort to less-preferred foods when their favorites can't be found.

"Long-term studies in the Allegheny National Forest show that as deer increase in an area, wildflowers and other ground cover species decrease," he says. "To compound the problem, deer generally avoid eating most ferns. As a result, large expanses of ferns cover the forest floor in many Pennsylvania woodlands."

To many people, a verdant blanket of ferns in an open, park-like forest is a beautiful site to behold. To foresters, however, these conditions are signs that something is very wrong, ecologically speaking. Without a vigorous growth of new tree seedlings, the future of the forest is in jeopardy, and animals that depended on the missing plants for food and shelter may not find what they need to survive.

"Studies in the Allegheny Forest show that high deer density causes a decrease in songbird diversity, in addition to the decreases in wildflower and ground cover species," Harmon says.

Invasive plants are another cause of decreased plant diversity in the forest understory, Harmon points out. Most invasive plants come from other parts of the globe. In their new home in Penn's Woods, they proliferate because the natural controls that keep the plants in check in their homelands do not occur here.

Such natural controls include specific diseases and insects. Like ferns, introduced species can take over a site, displacing native plants and preventing seedlings from developing into trees.

"If you are one of Pennsylvania's half-million forest landowners, take another look at your woodlands," Harmon advises. "Do you see a diverse array of native wildflowers and other low-growing plants? If not, do you have a sea of ferns or a predominance of just one or two types of plants? If so, chances are that deer or invasive plants are affecting your woodlands. While these are tough problems to address, there are resources available to assist you."

The Pennsylvania Forest Stewardship Program provides private forest landowners with information and assistance to promote healthy and productive forests. The program produces many free publications, including "Forest Stewardship Bulletin #9: Understanding and Conserving Biological Wealth in Our Forests," "Invasive Plants Fact Sheets," and "From the Woods: White-tailed Deer."

To request these publications or to learn more about the Forest Stewardship Program, call 1-800-235-WISE (toll-free), send e-mail to RNRext@psu.edu, or write to Forest Stewardship Program, Forest Resources Extension, The Pennsylvania State University, 7 Ferguson Building, University Park, PA 16802.

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EDITORS: Contact Rance Harmon at 814-863-0401 or e-mail rsh144@psu.edu.

Contact: Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-865-1068 fax