Box 1 - Forest Ecology

The influences that shape forest regeneration are only beginning to be understood. Forest change is often a continuing process, and foresters attempt preservation of what is a successional stage. This, of course, is not possible without some form of management. In many instances there may be no stable climax, since the overall environment is being altered by human activity and perhaps by climatic change.

Fire as all influence on forest succession has been recognized as having both beneficial and negative effects. It has always been an integral part of the forest environment, and it has contributed to a mosaic of successional subclimaxes within an overall species climax. For example, fire in a redwood forest may promote the growth of grassland, which is only slowly reconverted to redwood, depending upon the frequency of subsequent fires.

The succession that occurs in the northern Rocky Mountain forests is influenced by fire. Lodgepole pine is the offspring of fire, occurring in even aged stands after burning. If fire does not reoccur, species of Picea and Abies come to dominate, and, if fire control is exercised, they come to constitute the climax. The fact that lodgepole pine will not reproduce under its own canopy helps to explain the even aged stand.

On the other hand, wildfire can alter soil conditions so much that it prevents succession. This has been demonstrated in stands of ponderosa pine in the Southwest, where no new ponderosa catch occurs after burning even though reproduction takes place on land not burned. The soil constituency following fire–or for that matter after clear-cutting and the exposure this procedure brings–may materially depauperate the biological composition and influence forest quality far into the future.

In north-central Colorado, an outbreak of spruce beetles caused death of large-diameter spruce trees in patches, and altered the species composition of the forest in favor of fir and lodgepole pine. The outbreak developed in logging slash (and was thus an upset caused by people), but it remained epidemic for only 2 years, until natural competitors (for example, such parasites as nematodes, and woodpeckers, which lent great assistance) responded sufficiently to control the beetles.

As people assume greater influence in the forest through harvesting and attempted management, the balance and buffering characteristic of virgin forest can be expected to diminish. The rapidity with which natural forests are being cut allows little time for the research necessary to avoid habitat degradation.