Surveys in 1940 and the late 1980s show that the forests of Shenandoah National Park have changed dramatically in 50 years. The changes include the percentage of forested lands, and the ages, sizes, and species of trees. In 1940, Shenandoah was a young park. It was authorized by act of Congress in 1926 and established in 1935. For almost 200 years prior to park establishment people had harvested and used the resources of these mountains. Timbering, grazing, hunting, and cultivation ceased when these lands became a national park.
In 1940 the park was 85% forested. The rest of the park was open ground, including grasslands, cultivated fields, and old fields reverting to forest. Previously grazed areas were being occupied by bear oaks and pitch pines. By 1990 the park was 95% forested. In the more mature forest, bear oak stands had disappeared and pitch pine numbers had dwindled.
In 1940 there were no yellow poplar stands and cove hardwoods covered only 6% of the area. By 1990, yellow poplar stands covered 16% of the park and cove hardwoods covered 15%. These forest types grow in moist sites. Their increase is evidence of more organic matter in the soil and more adjacent protective forest canopy cover.
In 1940 chestnut oaks and northern red oaks covered 72% of the park. By 1990, their numbers were down to 59%. Since 1990 repeated defoliation by non-native gypsy moth caterpillars has contributed to the deaths of even more oaks.
What do these changes mean? The answer is not simple. For example, fewer oaks mean fewer acorns. Acorns are food for deer, bear, wild turkey, and other animals. In the short-term it also means there are more forest canopy openings. These openings result in greater diversity of species in the forest This means more berries and soft nuts that birds, bear, and deer use. Sometimes the end result of forest change is the complete loss of a species or loss of the species from the park. It can also afford the opportunity to non-native species to invade. These changes in species diversity are not desirable.
Aside from change brought about by sudden events such as flooding, ice storms, or wildland fires, most park visitors will not witness forest change. Successional change, response to natural disturbances, and encroachment of non-native species occurs gradually, taking years or decades. Despite the apparent snail's pace, change is vital to properly functioning ecosystems.