The concept of "ecosystem integrity" provides a basis for assessing restoration needs and proposals. An initial step is defining the terms "ecosystem" and "ecosystem integrity." An ecosystem is comprised of all of the organisms in an area interacting with their environment (Odum 1983). Ecosystem integrity, also known as ecosystem health, is "a desired condition of ecosystems in which productivity of resources and ecological values, including diversity, are resilient to disturbance and sustainable for the long term" (Reynolds 1995). In other words, ecosystem integrity involves maintaining biodiversity, biological productivity, and ecosystem processes. Important aspects of ecosystem integrity include energy flow through the food web, water and nutrient cycles, disturbance/recovery cycles, biotic diversity, evolutionary processes, and human influences. These characteristics and processes function at various rates and across multiple scales. Maintaining ecosystems requires maintaining the processes. It is not sufficient to preserve the individual pieces.

One of the difficulties of understanding, measuring, and managing for ecosystem integrity is the large number of factors that must be considered. Studying and restoring ecosystem integrity requires envisioning the system as a whole and discerning connections, general patterns, relative importance, and root causes (Reid et al. 1994, Orr 1995). Ecosystem components and processes occur and interact across virtually every spatial and temporal scale (Table 3). In the case of stream habitats, processes and elements that define these ecosystems and influence their integrity can be grouped into three categories: 1) soils/geomorphology; 2) hydrology; and 3) biota (Kauffman et al. 1997).

Ecosystem restoration requires knowledge about the patterns of change in ecosystem elements and processes and the causes for these changes. Contrary to the widespread belief in the "balance of nature", ecosystems are always changing and do not return to a particular equilibrium condition after disturbance (Botkin 1990, 1994). Ecosystem structure and composition fluctuate in response to combined influences from many controlling factors. Over the long term, controlling influences include climatic change, species migration, and evolution. In the short term, there are rapid changes in ecosystem conditions due to disturbances, such as storms and timber harvest. Furthermore, short-term disturbances also contribute to more gradual changes that cascade through the system. As ecosystem conditions stabilize following disturbance, the system will be different to some degree. The changes may be imperceptible or catastrophic. The ecosystem may contain many new species, or the same species may be present in different proportions.

Although ecosystems are continually changing, they tend to remain within the familiar range of conditions that have occurred repeatedly over centuries. This range of conditions for an ecosystem is called its "historic range of variability" (Morgan et al. 1994). Although ecosystems have evolved in association with constant change and have a level of resilience to change, they can be driven beyond the historic range of variability by natural events, such as volcanic eruptions, as well as human-induced events. Because of the combined influence of natural disturbances and modern human impacts, ecosystems are now more likely to be driven beyond their normal bounds. Several characteristics of ecosystems are useful for relating ecosystem conditions and trends to the historic range of variability (Table 4).

Another descriptor of the pattern of change in an ecosystem over time is "recurrence interval" (or "return period") for a particular ecosystem condition or event. Any particular ecosystem condition within the historic range of variability is expected to recur eventually. Recurrence interval is the average length of time between repetitions of a particular ecosystem event or condition (Botkin 1994). The normal range of conditions in an ecosystem and their pattern of occurrence provide a standard for evaluating present conditions, trends, and management options.

Although mean recurrence interval aids in understanding ecosystem processes, ecosystems are typically unpredictable. While some ecosystem conditions and events occur in an irregular pulsing pattern, in other cases there is no discernable pattern. For example, in California, precipitation occurs in a somewhat predictable pattern. However, droughts and deluges occur sporadically in an unpredictable fashion.

An important tool for assessing ecosystem conditions and trends is the "indicator species." An indicator species is a species that is sensitive to habitat quality and is monitored to provide insights into trends in habitat quality. In this way, status of indicator species is used to infer the status of many other species that depend on similar habitat (Meffe and Carroll 1994). Like the canaries that were used by miners to warn of the presence of toxic gases, indicator species provide an early warning of ecosystem deterioration.

In stream ecosystems, benthic macroinvertebrates and anadromous salmonids are important as indicator species. Benthic macroinvertebrates are aquatic insects that are useful in determining stream habitat conditions. Through sampling benthic macroinvertebrates from gravel in the stream bed, the recent history of water quality can be determined (Plafkin et al. 1989). Anadromous salmonids are an indicator species on a very broad spatial scale because their life cycle requires favorable conditions in many habitats at different times. Their populations are controlled by conditions in all the ecosystems they use (stream, river, estuary, ocean) as well as in migration corridors between these habitats.

Stream habitat conditions vary over multiple time frames; weekly, seasonally, and decadally. Understanding of these habitats is increased through observing the controlling influences on trends in the ecosystem. In river ecosystems, controlling influences include geomorphic processes and riparian vegetation. Habitats vary in a pulsing cycle of destruction and recovery driven by the combination of stream flow and geomorphic processes. It is a paradox that ecological integrity and fish habitat in coastal streams of northern California are maintained through periods of upheaval and instability as well as periods of relative stability. A disturbance to the system, such as a period of flooding and landsliding, reduces the quality of stream habitat for salmonids until a recovery period occurs. On the other hand, a complete lack of disturbance in the stream channel, as noted in river reaches below dams, also degrades fish habitat. Between continuous disturbance and lack of disturbance, there is a range of recurrence intervals for stream disturbances that provide favorable conditions for salmonids. In other words, salmonid habitat is maintained through alternating periods of stability and upheaval. The entire river ecosystem is adapted to and depends on an irregular pattern of upheaval and recovery. Over years and decades, as disturbance and recovery vary across the landscape, the location of high quality habitat changes and population densities of species shift accordingly.

During the destruction and recovery of stream habitats, there are important interactions between high stream flow and riparian vegetation. High flows periodically rip out riparian trees and prepare seed beds for regeneration of riparian trees. The age class structure of riparian species, such as alders and willows, is controlled by the sporadic occurrence of peak flows and related geomorphic processes. Riparian vegetation tells the story of several decades of change in the location of the stream channel as influenced by peak flows.

In the Smith River system, riparian trees are a "keystone species" due to their role in geomorphic and biological processes. A keystone species is a species that plays an exceptionally strong role in community processes or structure. The decline of a keystone species results in the decline of dependent species and drastic changes in community composition and the food chain (Meffe and Carroll 1994). Alder trees (Alnus sp.) that host nitrogen-fixing bacteria are probably keystone species because they supply nitrogen that helps maintain ecosystem productivity over the long term. Anadromous salmonids may also be a keystone species by virtue of their role in nutrient cycling. Over long periods, anadromous salmonids may be necessary for cycling phosphorous from the marine environment to inland areas (Cooperrider and Garrett 1995).

There are significant obstacles to understanding and restoring ecosystem integrity and anadromous fisheries. It is difficult to comprehend the interaction of many factors that influence river ecosystems and andromous fisheries. In addition, it is difficult to achieve the large scope of activities necessary to achieve effective ecosystem research and management. Managing anadromous fisheries requires methods of envisioning conditions throughout large river basins as well as continuity over long time periods. This leads to logistical problems including transcending administrative boundaries, such as state lines, and short time frames imposed by political election cycles. As a result of these difficulties, there is scientific uncertainty about the effectiveness of potential restoration strategies. Finally, restoration is controversial due to disagreement in the human community concerning resource use and environmental values. Simultaneously, there is immense pressure for immediate action despite scientific uncertainty and lack of consensus.

This page is hosted by Get your own Free Home Page