as ceanothus (Ceanothus spp.) and alder (Alnus spp.), are associated with early stages of succession. Others, such as the lichen mentioned earlier, are associated with old growth; still others (microbial) are associated with woody debris. Forest management activities have tended to eliminate these sources to minimize competition from noncrop species and speed development of a closed canopy of crop trees.
Efforts to conserve structural and functional diversity are often linked; for example, by maintaining woody debris, one of the sites for nitrogen fixation is retained within the ecosystem. Another example is maintaining large volume, complex crown structures that are especially effective at scavenging moisture and particulate materials from the atmosphere.
Obviously, maintaining structural and functional diversity is an objective that is broadly applicable to temperate landscapes and not just to forests. For example, continuous efforts are under way to convert complex shrub-steppes or savannas to grasslands or even monocultures of seeded grasses by eliminating woody plants such as sagebrush (Artemisia spp.) or junipers (Juniperus spp.). Such programs are capable of causing great damage to structural, functional, and genetic diversity over large areas.
Protecting aquatic diversity, including that of the riparian zones, is one of the most difficult tasks within the temperate zone. Streams and rivers have been dammed, diverted, and polluted. Organisms have been extirpated and many new organisms introduced, either purposely or accidently. Control of large land areas (watersheds) is required to provide complete protection for many bodies of water (Figure 18–3). Legal problems are often overwhelming in view of the large number of jurisdictions involved and, at least in the United States, the peculiarities of water rights and law.
The risk to aquatic biodiversity within temperate regions is great and has not received much effective attention, despite the attention given waterfowl and fisheries and the recognized importance of wetlands. Loss of diversity in river ecosystems may be particularly serious and certainly affects invertebrates (e.g., insects and molluscs) as well as vertebrates (e.g., fish). One need only be reminded of the loss of anadromous fish from many river systems after dams were built to realize that these changes involve loss of other important compositional, structural, and functional features from these ecosystems as well.
Developing effective programs to protect aquatic biodiversity is a priority of the highest order. Even the initial step—an adequate analysis of the problem—will require additional research as well as syntheses of existing information. Creative new approaches to conservation will be required, such as acquisition of water rights and licenses for dam construction. The Nature Conservancy has pioneered development of such creative approaches in their recent wetlands initiative.
Protecting aquatic biodiversity is a problem in all segments of the temperate zone—from forests to deserts. The most critical problems in protecting aquatic