Succession

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Much of what we see as original forest in the Eastern Deciduous Forest was at one time agricultural fields. If you wander around the wooded hills and valleys in upstate New York you feel as if this was always forest. However old photographs of the region show that almost all of the land was small farms and even today as you move through the forest you are continually finding the foundations of old farms scattered among the trees. Given a chance, however, cleared fields will return to Eastern Deciduous Forest by the process known as succession.

Consider the following experiment. Clear the trees from an area, remove the stumps, and plow the ground. Now let the cleared field stand for many years. At first the field will be colonized by weedy species of plants specializing in finding disturbed areas and reproducing rapidly. After a few years, however, perennial plants such as grasses, goldenrods, and asters will move in and replace the original weedy species (top picture on the left). In turn the field will be invaded by the first of the trees. The pioneering trees are commonly Eastern Red Cedar, possibly pines, and shruby trees such as Hawthorn and Serviceberry. At first these small trees will be scattered throughout the field, but later the trees will dominate the perennial plants. Light is reduced at the soil surface and the soil becomes better able to retain water. Soil nitrogen and organic matter increases. Other trees begin to colonize, typically species of birch and cherry and young individuals of the forest that will eventually result from succession. The earlier small pioneer trees have relatively short life spans and under the increasingly closed conditions of the woods (for woods it now is) are replaced by a tangle of young trees.

Among this tangle of young trees appear the young seedlings of the trees of the final forest. These longer lived trees such as Beech, Oak, and Maple grow best under wooded conditions of decreasing light and increased soil moisture and nutrients. The shorter lived and smaller trees (such as the birches and cherries) are overgrown by the dominant trees and slowly disappear. The forest eventually becomes open underneath dominated by large, tall trees. In the open rich soils underneath spring wildflowers become abundant (bottom picture on the left).

Nothing in nature, however, is as cut and dry as this description makes it sound. Chance plays an important part in what species arrive and when. Time changes not only the species composition of the area, but also the environmental conditions. The seeds of a climax dominant species may arrive early during the process, but not survive because the conditions are not right. Conversely a dominant species may never appear in the forest simply because the seeds never made it there even though the species would do just fine there if it had colonized.

In some areas a climax forest is never reached. In the southeastern United States are extensive stands of pines on soil types that should support deciduous trees. Given time these stands of pines would be replaced by deciduous trees. However every few years the pine forest burns. The pine trees are adapted to surviving fire and sometimes time their reproduction to the burns. Deciduous seedlings, however, are not adapted to fire and are eliminated. The pine stands remain. This is called a fire disclimax.