Chapter 1. Biodiversity
Overview of Biological Diversity and Ecosystem ManagementOctober 2003
The natural systems of California are complex. They function at different scales of space and work in different scales of time. For the purposes of this Assessment, FRAP uses the concepts of biological diversity and the ecosystem as a way to organize the discussion of the status and trends of forest and rangeland elements.
What is an ecosystem?
An ecosystem can be considered as a model to organize and characterize observations about natural systems and their interrelationships. Just as the body contains different organs, an ecosystem contains different elements that move energy, sustain life, and influence one another. Three elements of any ecosystem are components, structure, and process.
Three ecosystem elements
The interaction among ecosystem elements at a variety of spatial scales creates an endless problem of measurement, while offering an opportunity to focus a logical structure for management and decision-making. Ecosystem functions (the interaction of components, structure, and process) generally exhibit patterns that can be organized by scale (e.g. populations, species, landscapes, bioregions) in a hierarchical manner. This nested organization can facilitate both analysis and understanding. By using this approach, managers can assume that by conserving the system at a particular scale they have a higher probability of conserving the smaller component parts as well. An ecosystem approach allows managers to move ahead in promising directions while monitoring results. It does not depend on systematic inventories and ecological studies that may never be fully implemented.
Important characteristics of ecosystems related to biological diversity
Disturbance: Unpredictable changes to ecosystem elements are disturbances. Disturbances like fire or flooding characterize a landscape and can affect ecosystem function. Disturbances are characterized by intensity (degree of disturbance), timeframe (frequency, return interval), and space (area, size). These “ecosystem drivers” can be generally characterized as natural, such as fire or flood, or human-related, such as urbanization or land management. For the purposes of this assessment, natural disturbance processes include fire, water flow, wind/air, insects/disease, climate, vegetation dynamics, and physical processes (landslides, etc). Human induced disturbance comes from management for resources (wood, forage), conversion to agriculture, urbanization, introduction of exotic species, spread of forest pests, and discharge of wastes into the air, water, and soil. Disturbance will be further discussed in Chapter 3, which analyzes threats to forest health and vitality.
Scale: Scale refers to the size of ecosystem elements or “ecosystem drivers” used for analysis. Many different scales—from the individual tree to the forested stand to the watershed to the bioregion—can be used to analyze ecosystem function. The scale that is selected and the boundaries that are used are based on the problem or question at hand. For the purposes of this assessment, FRAP primarily uses the scale of a planning watershed (a 3,000-10,000 acre area where water flows to the same streams or river basins), bioregions, and the State as a whole. Bioregions generally follow aggregations of watersheds and river basins.
Ecosystems are dynamic and exhibit resilience: There is not a single “natural condition” or “balance of nature,” but a variety of conditions that could be considered natural (Botkin et al., 1993). Resources must be managed with the understanding that plant and animal populations will vary over scales of space and time with or without human intervention. Ecosystems change “over space and time in response to inputs of energy, new species, natural events, internal growth and development processes, and how people treat the land” (Salwasser and Pfister, 1994). This change happens through succession, which may occur gradually, or in discrete shifts along a number of different pathways. Succession is developmental change that occurs through the interaction of vegetation, the environment, and disturbance. Successional patterns are the structural evidence of processes and disturbances that characterize a place.
One measure of the ability of a landscape to respond to a disturbance is its resiliency, which is its ability to return to a similar state. Another closely related measure is ecosystem resistance, the ability to maintain characteristic components, structures, and processes in the face of disturbance. Resiliency and resistance can interact. To illustrate, an ecosystem disturbed beyond limits of resistance and resilience and in a relatively short time frame is found in the sagebrush-steppe plant community of the eastern Sierra Nevada and northeastern California. In this area, the effects of destructive grazing practices in the 1800s, introduction of exotic annual grass species, and subsequent change in fire size, frequency, and intensity have changed a perennial grass dominated system to one dominated by sagebrush and other shrubs and more recently to one dominated by introduced annual grasses. Ecosystems that are resilient, but with low resistance, will exhibit large fluctuations but persist for an extended period of time. Conversely, an ecosystem with high resistance, but low resilience, will rarely fluctuate but may not persist in the face of significant stressors (Odum et al., 1987).
Human populations and ecosystems are linked: At the core of ecosystem management and the conservation of biological diversity is the recognition that humans and ecosystems are linked. The collective needs and aspirations of people, whose well being is dependent on ecosystems will determine the current and future condition of ecosystems (Salwasser and Pfister, 1994).
Ecosystem management to maintain management options
Within the United States, there are many different concepts of resource management. These carry over into understanding of ecosystem management as well. Ultimately, biological diversity and ecosystems will be shaped by the management decisions of humans. These decisions determine society’s ability to maintain viable populations and other ecological elements. Yaffee (1999) has summarized the range of possible resource management philosophies as they have been applied to land-use policy (see table below).
Continuum of natural resource management philosophy (adapted from Yaffee, 1999)
High uncertainty deters early consensus on the best approach to achieving ecosystem management. There must be a balance between the time required to better understand ecosystem complexity and the need to make management decisions. The dynamic nature of ecosystem function further complicates the task of describing desired future conditions to guide management decisions. Defining appropriate management boundaries is also complicated when processes and politics are arranged differently in space and time. Further difficulties to making land-use policy using an ecosystem approach include dealing with real value differences between societal groups and determining if past approaches have worked well (Yaffee, 1999).
Uncertainty and ecosystem management: emulating ecosystem function to maintain biological diversity.
California’s land base is no longer large enough to absorb the variety of needs and byproducts of the current and growing population and economy and still maintain management options in the face of ecological uncertainty. This condition expresses itself in a variety of ways, but includes declining numbers of plant and animal species, fragmented and simplified habitats, increasing numbers of invasive exotic species, and other measures related to biological diversity and ecosystem health. To a significant degree, California has adjusted to some of these changes through the increasing import of many necessary commodities such as oil, natural gas, timber, and basic foods. Conversely, California has a higher population growth rate than the nation as a whole.
Although rapid advances have been made in environmental sciences during the past several decades, pertinent historical data seldom have been collected at the appropriate scale of space and time. In many cases, the impacts of human activities are still unfolding. The result is incomplete understanding of the processes that determine change in these systems over time and decision-making uncertainty that accompanies that information void. Finally, what future generations will value in ecosystems is not known. What mix of ecosystem values are emphasized to benefit future generations? As a society, how scientific information and knowledge will contribute to the development of environmental policy has not been determined. In many cases, society is still operating under Leopold’s “save all the parts” (the components) injunction, whether they can save them or not, rather than “saving ecological processes and permitting them to operate.” Ecosystem management—to be successful as an approach to resource allocation and the maintenance of biological diversity—must be able to reduce polarization of interests and help reach social consensus on natural resource management objectives. In this sense, ecosystem management is no less complex than other social and economic systems.
The conceptual foundations of ecosystem management and conservation of biological diversity have developed most consistently since the late 1980s. Risser (1987) called for the rejection of myths regarding ecosystem function, including the notions that 1) fundamental understanding of ecological systems is only achieved with research conducted on natural, undisturbed systems; 2) ecosystems move toward equilibrium regardless of scale or disturbance; and 3) humans are separate from ecological systems. Assertions regarding managing for sustainability are considered suspect in the face of the complexity of ecosystems, a changing environment, and the influence of human use. Rather than claiming sustainability in resource management goals, decision-makers must address options to manage for uncertainty.
An ecosystem management approach to the conservation of biological diversity recognizes land as a community of soils, water, and biota. Implementation of the approach requires going beyond the notion that endangered species and biological diversity will be sustained solely with additional land placed in reserves. Ecosystems function at geographic scales larger than existing parks and refuges relative to the maintenance of viable population and biological diversity. It is highly unlikely that significant additions to these lands will be realized or even effective in sustaining resources. The customary resource management approach of deciding what resource must be preserved and segregating it from the rest can have only limited results (Salwasser, 1991).
Recognition of the overriding role of environmental uncertainty also produced change in the perception of environmental issues, in the ability to deal with these issues, and in the context with which these issues are viewed (Botkin, 1990; Botkin et al., 1993). Many resource management decision-makers assume that, given enough research and the right models or other analytical approaches, exact numbers can be determined for population size, components of population dynamics, and the responses of populations to harvest levels. This assumption is nearly always erroneous. Many things about the environment cannot be measured in an exact manner and typically there are “chance events” (e.g. “ecosystem drivers” such as below or above average precipitation, change in fire regime, etc.) that influence the outcome of any natural process.
In light of current uncertainty about ecological relationships, recent approaches to ecosystem management focused on emulating (in contrast to duplicating) ecosystem components, structure, and process. This is evident in the focus on reversing habitat fragmentation, increasing or maintaining important ecosystem components—such as old growth forests or special habitats—attempts to gauge influence of past fire regimes, and in addressing toxic waste, water, and air quality. For example, Williams et al. (1999) suggest adoption of an anadromous fish life history ecosystem concept as a guide to recover depressed salmon stocks. Natural river processes are templates on which salmonid life histories, stable multi-stock productivity, and long-term continuity depend. Some approaches to salmonid recovery have mistakenly emphasized activities and actions that circumvented the natural ecological attributes of riverine function. The implementation of the concept of a “normative river” (e.g. where humans emulate nature relative to water flow regimes) holds the most promise.
Assessment on-line technical reports summarizing Chapter 1: Conservation of Biological Diversity
Within the context of biological diversity, the Montreal Process has identified nine indicators for assessing conservation of biological diversity. FRAP has chosen to respond to these indicators by presenting the six on-line technical reports which focus on the area, composition, and structure of habitats. While these technical reports do not completely and precisely address all the indicators, FRAP has collected and evaluated information that is most applicable to the forest and rangeland settings in California.
The six on-line technical reports in Chapter 1: Conservation of biological diversity include the following: Habitat Diversity discusses statewide land cover, forest and rangeland habitat as it relates to ownerships and management settings, and underrepresented habitats. Habitat Elements focuses on the current distribution of standing dead trees (snags) and coarse woody debris (down logs) on various habitats and ownerships. Old Growth Forests reviews the status of large, old trees sometimes referred to as old growth, late successional forests, or legacy stands. Hardwoods report includes hardwood acreage, change detected in canopy cover and the causes of that change, as well as historic and projected changes to the hardwood land base. Population Status of Native Species discusses the numbers of native species in forest and rangelands of the State including the patterns of species richness, fish distribution, and game and furbearing species population trends. The final report, Species of Concern, focuses on threatened and endangered species as identified by regulatory agencies.
Each document is linked in a separate Adobe Acrobat pdf format below.
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