Saving Nature's Legacy: Protecting And Restoring Biodiversity
443
Saving Nature's Legacy: Protecting And Restoring Biodiversity
443Overview
Written by two leading conservation biologists, Saving Nature's Legacy is a thorough and readable introduction to issues of land management and conservation biology. It presents a broad, land-based approach to biodiversity conservation in the United States, with the authors succinctly translating principles, techniques, and findings of the ecological sciences into an accessible and practical plan for action.
After laying the groundwork for biodiversity conservation -- what biodiversity is, why it is important, its status in North America -- Noss and Cooperrider consider the strengths and limitations of past and current approaches to land management. They then present the framework for a bold new strategy, with explicit guidelines on:
- inventorying biodiversity
- selecting areas for protection
- designing regional and continental reserve networks
- establishing monitoring programs
- setting priorities for getting the job done
Product Details
| ISBN-13: | 9781610913218 |
|---|---|
| Publisher: | Island Press |
| Publication date: | 02/22/2013 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 443 |
| File size: | 22 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Read an Excerpt
Saving Nature's Legacy
Protecting and Restoring Biodiversity
By Reed F. Noss, Allen Y. Cooperrider
ISLAND PRESS
Copyright © 1994 Defenders of WildlifeAll rights reserved.
ISBN: 978-1-61091-321-8
CHAPTER 1
BIODIVERSITY AND ITS VALUE
The earth never tires:
The earth is rude, silent, incomprehensible at first—Nature is rude and incomprehensible at first;
Be not discouraged—keep on—there are divine things, well enveloped;
I swear to you there are divine things more beautiful than words can tell.
Walt Whitman (1856), Leaves of Grass
This book is an exercise in applied conservation biology. The fundamental question of conservation biology is a critical one: how can the variety of life be maintained in perpetuity? How can we help preserve "divine things more beautiful than words can tell"? No one has an answer to these questions. But scientists have learned a few things about how nature works and what kinds of human activities are compatible and incompatible with life on earth. In this chapter, we first define biodiversity and describe its major components, then discuss why diversity has become an issue in the United States. This leads into a discussion of the values of biodiversity and why management of biodiversity has become a regrettable necessity today.
What Is Biodiversity?
In little more than a decade, biodiversity progressed from a short-hand expression for species diversity into a powerful symbol for the full richness of life on earth. Biodiversity is now a major driving force behind efforts to reform land management and development practices worldwide and to establish a more harmonious relationship between people and nature.
Biodiversity. A symbol? An issue? A driving force? It would be easier if biodiversity could be measured by the quantity of bird species in a forest, wildflowers in a meadow, or beetles in a log. But simplicity is not one of the virtues of biodiversity. Ecosystems are more complex than we can imagine. Our most intricate machines—say, a space shuttle and all its ground-control computers—are simple toys compared to an old-growth forest, its myriad known and unknown species, and their intricate genetic codes and ecological interactions. Just identifying and counting species is difficult enough. The almost infinite complexity of nature defies our best efforts to classify, categorize, or even describe.
A common misconception is that biodiversity is equivalent to species diversity—the more species in an area, the greater its biodiversity. However, biodiversity is not just a numbers game. On a global scale, maintaining maximal species richness is a legitimate goal and requires keeping global extinction rates low enough that they are balanced or surpassed by speciation. When we consider species richness at any scale smaller than the biosphere, quality is more important than quantity. It is not so much the number of species that we are interested in, it is their identity. Fragmenting an old-growth forest with clearcuts, for example, would increase species richness at a local scale but would not contribute to species richness at a broader scale if sensitive species were lost from the landscape.
Diversification can all too easily become homogenization. The greatest cause of homogenization worldwide is the introduction of nonnative plants and animals, often called exotics. Exotics are species that have invaded new areas due to accidental or deliberate transport by humans. Although species naturally disperse and colonize new areas, so that floras and faunas change continually over long periods of time, human transport and habitat disturbance have greatly increased the rate and scale of invasions. Many regions have nearly as many exotic as native species today. Introductions of exotics may increase species richness locally or even regionally, but they contribute nothing positive to biodiversity. Rather, they pollute the integrity of regional floras and faunas and often alter fundamental ecological processes, such as fire frequency and intensity, and nutrient cycles. Thus, whole ecosystems are changed. Regions invaded by exotics lose their distinctive characters. Every place begins to look the same. The result is global impoverishment. For these reasons, we emphasize native biodiversity, not diversity per se.
The important task is not to define biodiversity, but rather to determine the components of biodiversity in a region, their distribution and interrelationships, what threatens them, how we measure and monitor them, and what can be done to conserve them. These topics are the subject of this book. But because working definitions are helpful to summarize what we are talking about, we propose the following modification of a definition developed by the Keystone Dialogue (Keystone Center 1991):
Biodiversity is the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever changing and adapting.
This definition recognizes variety at several levels of biological organization. Four levels of organization commonly considered are genetic, population /species, community/ecosystem, and landscape or regional. Each of these levels can be further divided into compositional, structural, and functional components of a nested hierarchy (Noss 1990a). Composition includes the genetic constitution of populations, the identity and relative abundances of species in a natural community, and the kinds of habitats and communities distributed across the landscape. Structure includes the sequence of pools and riffles in a stream, down logs and snags in a forest, the dispersion and vertical layering of plants, and the horizontal patchiness of vegetation at many spatial scales. Function includes the climatic, geological, hydrological, ecological, and evolutionary processes that generate and maintain biodiversity in ever-changing patterns over time.
Why bother with this cumbersome classification? Because nature is infinitely complex. Unless we try to identify and classify the forms of this complexity, we are likely either to miss something or become hopelessly confused. If something falls through the cracks in our conservation programs, it may be lost forever. With each loss biodiversity is diminished. The earth becomes a less interesting place.
Conserving biodiversity, then, involves much more than saving species from extinction. As implied by our characterization of biodiversity, biotic impoverishment can take many forms and occur at several levels of biological organization. Hence, steps must be taken at multiple levels to counteract impoverishment. Below, we review some conservation issues, goals, and problems that can be addressed at each of four major levels of biological organization. We emphasize that a comprehensive conservation strategy must integrate concerns from all levels of the biological hierarchy.
GENETIC LEVEL
Genes, sequences of the DNA (deoxyribonucleic acid)molecule, are the functional units of heredity. Species differ from one another and individuals within species vary largely because they have unique combinations of genes. Gene frequencies and genotypes (individual organisms with a particular genetic make-up) within a population change over time as a consequence of both random and deterministic forces. Random changes include mutations that create new genes or sequences of genes, and loss of genes by chance in small populations (called sampling error or genetic drift). Deterministic changes include natural and artificial selection, where some genotypes are more successful reproducers than others. In the long run, genetic change leads to evolutionary change as individuals adapt to different situations and pass on their new traits to offspring. Genetic diversity is fundamental to the variety of life and is the raw material for evolution of new species. We will discuss evolution briefly in Chapter 2.
Conservation goals at the genetic level include maintaining genetic variation within and among populations of species, and assuring that processes such as genetic differentiation and gene flow continue at normal rates. Without genetic variation, populations are less adaptable and their extinction more probable, all else being equal. Small, isolated populations are more likely to diverge genetically, having fewer chances for genetic mixing with other populations. But at the same time small, isolated populations are more likely to suffer from inbreeding depression caused by mating between close relatives, which may result in reduced fertility and other problems (Frankel and Soulé 1981). Small, isolated populations also are subject to random loss of genes (genetic drift), which restricts their ability to adapt to a dynamic environment.
Conservationists talk much about saving the earth's genetic resources. But with the exception of some agricultural crops, commercial tree species, populations of rare vertebrates in zoos, and a handful of wild populations, we know very little about genetic diversity. Land managers seldom think about maintaining biodiversity at the genetic level. If our vision of conservation is long term, however, genetic variation must be better understood for all organisms.
SPECIES LEVEL
The species level of diversity is probably what most people think of when they hear the term biodiversity. Although in some ways species diversity is the best known aspect of biodiversity, we should bear in mind that the vast majority of species in the world are still unknown. Of an estimated 10 to 100 million species on Earth (Wilson 1992), we have named only about 1.8 million (Stork 1992). Known species are dominated by insects, half of them beetles (Fig. 1.1). But many invertebrates, bacteria, and other organisms remain to be discovered, even in the United States. Hundreds of invertebrate species can be found in one square meter of soil and litter in an old-growth temperate forest (Lattin 1990). Even more amazing, Norwegian microbiologists found between 4000 and 5000 species of bacteria in a single gram of soil from a beech forest. About the same number of species, with little overlap, was found in a gram of sediment from off the coast of Norway (Wilson 1992). These findings raise the question of whether the tropical rainforests really are the most diverse habitats on Earth. We know too little about biodiversity to conclude much with certainty.
A population is a local occurrence of a species and is the unit that we usually manage. Conservation goals at the population/species level include maintaining viable populations of all native species in natural patterns of abundance and distribution. These goals grade into community-level goals of maintaining native species richness and composition, as discussed below
Despite the problems and biases of single-species management, many species require individual attention, particularly when they have become so rare that heroic measures are needed to save them. In addition, certain kinds of species warrant management emphasis because their protection will conserve more than themselves. Especially important in this regard are keystone species, which play pivotal roles in their ecosystems and upon which a large part of the community depends (Noss 1991a). The importance of a keystone species is often disproportionate to its abundance. The beaver, for instance, creates habitats used by many species and also regulates hydrology and other ecosystem functions (Naiman et al. 1988). If we reduce beaver numbers through heavy trapping, then all else being equal, we impoverish the landscape. The beaver is not an endangered species, but it is greatly reduced or even absent from many regions where it was once abundant. Major declines of keystone species are more important ecologically than the loss of the last few individuals of rare species that play minor roles in their communities. This said, we must recognize that the term keystone species is poorly defined. Instead of a dichotomy of keystones and nonkeystones, communities may be better characterized by a wide range of interactions of variable strengths (Mills et al, 1993). Because we know so little about the ecological roles of species, each species must be considered important.
Some kinds of species have great pragmatic value for conservation, especially those we can characterize as "umbrellas" or "flagships" (Noss 1991a). To illustrate the umbrella concept, consider a carnivore (such as a grizzly bear or wolf) that requires millions of acres of land to maintain a viable population. If we secure enough wild habitat for these large predators, many other less-demanding species will be carried under the umbrella of protection. Umbrella species are often charismatic, so they also function as flagships or symbols for major conservation efforts. The grizzly bear, for instance, is a potent symbol for wilderness preservation in the northern Rocky Mountains. No umbrella is complete, however. Some endemic plant species have very small ranges—perhaps restricted to a single rock outcrop—that might not be protected in an ideal wilderness network established for grizzlies.
Animals and plants that are highly vulnerable to human activity often need to be managed individually, at least until their habitats can be protected by an ecosystem-level approach. Otherwise, biodiversity will continue to diminish with each extinction. Although we might accept the egalitarian notion that all species are ultimately equal, at any given place and time some species thrive on human activity and others suffer. Familiar examples of species that are extremely vulnerable to human activity are the northern spotted owl, threatened by logging of old-growth forests in the Pacific Northwest (Thomas et al. 1990); the red-cockaded woodpecker, endangered by logging of longleaf pine forests in the Southeastern Coastal Plain (Jackson 1986); and the desert tortoise, often shot or run over by motorized recreationists, forced to compete with livestock, collected for pets, and now ravaged by disease (U.S. Fish and Wildlife Service 1993). Species declines are signals that the environment is not healthy, but vulnerable species often require intensive care above and beyond immediate protection of their habitat.
COMMUNITY OR ECOSYSTEM LEVEL
In many cases, conservation is most efficient when focused directly on the community or ecosystem. A community is an interacting assemblage of species in an area. Terrestrial communities are usually defined by their dominant plants (for instance, the beech-maple forest), but functional or taxonomic groups of animals (for example, bird communities, lizard communities, herbivore communities) are also recognized. Functional groups of organisms (species that use a set of resources in similar ways, such as bark-gleaning birds) are often called guilds. Similarly, aquatic communities may be taxonomically or functionally defined, for example fish communities or littoral (shoreline) vegetation.
An ecosystem is a biotic community plus its abiotic environment. Ecosystems range in scale from microcosms, such as a vernal pool, to the entire biosphere. Many ecologists equate the terms ecosystem and community, except that ecosystem ecologists emphasize processes more than species and other entities. The Nature Conservancy defines natural communities by their most striking characteristics, whether biotic or abiotic. Thus, coastal plain pond, rich graminoid fen, black spruce- tamarack bog, and rich mesophytic forest are all described communities of New York State (Reschke 1990). These communities might also be called ecosystem "types." The variable spatial scale of ecosystems confuses the issue sometimes. Although scientists usually think of ecosystems as relatively discrete and existing at the same spatial scale as natural communities, conservationists often use the term ecosystem to encompass many different communities. For example, the Greater Yellowstone Ecosystem covers a diverse region of 14 to 19 million acres (see Chapter 5).
We consider conservation at the community or ecosystem level to complement, not replace, species-level management. The rationale for protecting ecosystems is compelling: if we can maintain intact, ecologically functional examples of each type of ecosystem in a region, then the species that live in these ecosystems will also persist. Representing all native ecosystems in a network of protected areas is the most basic conservation goal at the ecosystem level (see Chapter 4). Opportunities for adequate representation of ecosystems are being rapidly diminished as many of our native vegetation types are being reduced in area and degraded in quality (Noss et al. 1994).
(Continues...)
Excerpted from Saving Nature's Legacy by Reed F. Noss, Allen Y. Cooperrider. Copyright © 1994 Defenders of Wildlife. Excerpted by permission of ISLAND PRESS.
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Table of Contents
About Defenders of WildlifeTable of Figures
List of Tables
Foreword
Preface
Acknowledgments
Chapter 1. Biodiversity and Its Value
Chapter 2. Biodiversity: Creation and Destruction
Chapter 3. Conservation Strategies—Past, Present, And Future
Chapter 4. Selecting Reserves
Chapter 5. Designing Reserve Networks
Chapter 6. Managing Forests
Chapter 7. Managing Rangelands
Chapter 8. Managing Aquatic Ecosystems
Chapter 9. Monitoring
Chapter 10. The Task Ahead
Epilogue
Literature Cited
Glossary
Species List
Index