necessary) natural area preserves within intensively utilized landscapes. There is also a critical need to integrate biodiversity objectives into management of all our landscapes because preservation of selected tracts of land, even at the largest scale possible, will not by itself achieve the desired goal of maintaining Earth’s biodiversity.
Preserving biodiversity in temperate regions requires the maintenance of all successional stages. Since early successional stages are typically well represented, a major concern is preserving or recreating old-growth forests. Such old-growth forests typically contrast sharply with early successional stages in composition, structure, and function.
Most forests in the temperate zone are secondary forests that developed after logging of primeval forests or abandonment of agricultural lands. In the United States, these forests are typically young, having originated during the last 100 to 150 years. The composition and structure of these forests are different—often drastically different—from those they have replaced. We see, for example, forests of birch (Betula spp.) and aspen (Populus spp.) in the Great Lakes states, where the forests were originally dominated by long-lived pioneer species, such as red and eastern white pine (Pinus resinosa and P. strobus), and late successional species of hardwood.
Old-growth temperate forests dominated by coniferous species still cover substantial acreages in the western United States; research in these forests is clarifying the contrasts between young- (e.g., <100 year) and old-growth (e.g., >200 year) forests (see, e.g., Franklin et al., 1981). For example, old-growth forests of Douglas fir and western hemlock (Pseudotsuga menziedii and Tsuga heterophylla) (Figure 18–1) provide essential habitats for a set of highly specialized vertebrate species, including the northern spotted owl (Strix occidentalis). Research presently under way will provide a definitive list of old-growth-dependent species within these temperate conifer forests. This list may include several other birds, several mammals (bat species may be notable), and several amphibians (particularly salamanders). Such forests are also very rich in mosses, lichens, and liverworts, of which at least one species—a lichen—is strongly related to old-growth forests. That species, Lobaria oregana, is an important nitrogen-fixing foliose lichen that grows in the crowns of old-growth Douglas-fir trees. Research will almost certainly show that some of the rich invertebrate community is also old-growth-dependent; more than 1,000 species have been identified within a single old-growth stand, the upper bole and crown providing particularly rich habitat. The old-growth forests obviously have a high genetic content and are far from the biological deserts that some game biologists and foresters once suggested.
Functional differences between old-growth and younger forests are often qualitative rather than quantitative. That is, forests at all stages fix and cycle energy or carbon, regulate hydrologic flows, and conserve nutrients. Some stages carry out these activities more efficiently than others, however. Old-growth forests in the Douglas-fir region are particularly effective at regulating water flows and re-