Planning for Biodiversity

Issues and Examples

By Sheila Peck

ISLAND PRESS

Copyright © 1998 Sheila Peck
All rights reserved.
ISBN: 978-1-55963-401-4

Contents

About Island Press,
Title Page,
Copyright Page,
Dedication,
Acknowledgments,
Introduction,
Chapter 1 – Exploring Biodiversity,
Chapter 2 – Developing Conservation Priorities,
Chapter 3 – Change and Disturbance,
Chapter 4 – Area and Connectivity,
Chapter 5 – Reserve Design,
Chapter 6 – Collecting Baseline Information,
Chapter 7 – Monitoring and Adaptive Management,
Appendix – Planning Guidelines,
Notes,
Glossary,
Bibliography,
Index,
Island Press Board of Directors,

CHAPTER 1

Exploring Biodiversity

Mount Diablo, located in a state park east of San Francisco Bay, is known for its unique and varied species. The forty-minute drive to the top winds through numerous associations of oak, chaparral, pine, and grassland. The texture of the landscape is striking: a tapestry of interdigitating vegetation types, ranging from sparse blue oak savanna to tightly woven mats of brush. Shoots sprout from a recent burn, streams flow from winter rains, and exotic plants line the roadway. Image follows image, each one registering another facet of life on the mountain. Each is a part of the biodiversity of Mount Diablo.

How would one characterize biodiversity in this landscape? A way to begin would be to record the number and types of species, noting the presence of any that were rare or endangered. This approach, however, would yield only part of the picture. Another aspect of biodiversity is the ecological relationships that help establish and sustain species. For example, the vegetation patterns just observed and processes such as fire, water flow, and dispersal would all contribute to the present range of animals and plants. It is also important to portray biodiversity at different levels of biological organization. For instance, in addition to species, the description should include variations in the biotic communities of the mountain and in certain populations of species. Lastly, it should indicate how the different aspects of biodiversity fluctuate over time.

A biodiversity framework can be developed from these ideas. It consists of the components, patterns, and processes of ecosystems, each existing at multiple levels of organization and all varying over time (figure 1.1). By incorporating all three ecosystem attributes (components, patterns, and processes), not only can specific variations in the biota be considered, but so can many other factors on which this diversity depends. Similarly, addressing different levels of organization ensures that a range of these attributes is included. By estimating temporal variations, one can assess how representative today’s conditions are of those that have occurred over a longer period of time.

This framework has several uses for planners. Most important, it promotes a comprehensive approach to biodiversity planning and management. It clarifies the extent of the concept and suggests a method to address biodiversity beyond legal requirements or immediate issues. In addition, it is helpful at specific stages of the planning process. It is useful for understanding which parts of an issue are significant and the relationships between these parts. It provides guidance in deciding which types of information to collect, which types of analysis might be important, and which aspects of the system should be monitored and over what period of time. It is basic to conserving biodiversity in the landscapes we value.

Components, Patterns, and Processes

For most people, the term biodiversity evokes images of species, especially charismatic mammals, on the road to extinction. Species are the components of ecological systems about which they care the most. The public is well aware that organisms are vanishing rapidly in many areas of the world. Locally, they may be involved in developing plans to conserve species diversity. These plans might prioritize biotic communities that support a high number of plants and animals. They might also target species that are ecologically valuable or vulnerable. On Mount Diablo, for example, riparian and oak woodlands include substantially more native species than those occuring in annual grasslands. Acorn woodpeckers are valuable because they excavate tree cavities and so create nesting habitat for other birds and small mammals. Other species might be included in a plan because they are endangered, occur only on the mountain, or exist here hundreds of miles from their nearest relatives.

Species, of course, are not the only levels at which an ecosystem exhibits diversity. Communities also vary. A biotic community is any group of plants, animals, bacteria, and fungi that occurs together at a particular place and time. Species themselves are comprised of populations, or subsets of individuals that regularly interbreed. The number of populations in a species and the number of individuals in a population can be great or small. Genetic diversity, or the differences contained in the genes of a species or population, can also range from high to low. Additionally, differences in abiotic, or nonliving, factors—such as land use, soils, geology, climate, slope, and aspect—influence biological diversity.

While the components of ecosystems are often the focus, biodiversity is more than these parts. Systems by definition are sets of interacting elements, and these elements cannot exist alone. Each living part of an ecosystem is related in numerous ways to other living and nonliving parts. Thus to conserve biodiversity, what is needed is a model that addresses not only the components of ecosystems, but the relationships that occurs among them. To do this, patterns and processes are added to components as the foundation of the framework (figure 1.2).

It is the pattern of the vegetation as much as its composition that one notices on Mount Diablo. Each hillside contains several distinct community types. Moreover, these vegetation patches clearly correspond to specific environmental conditions. Grasses predominate on the dry, sunny, south slopes, while the cooler north sides support chaparral. Coast live oak and bay laurel also grow on the north slopes and extend like fingers up the canyons where more moisture exists. Blue oak savanna covers the bottom of the mountain, while canyon live oaks occur only at the top. Intermittent and perennial streams support separate associations of vegetation. Along some patches edges are ecotones, or overlap zones between two communities, with their own hybrid suite of species.

Other ecological patterns can be found within biotic communities. Savannas, for example, have a two-storied structure consisting of overhead tree canopy and underlying grasses and forbs. Most other oak woodlands include a third layer of shrubs. Dense chaparral is a haven for small animals and can be virtually impenetrable to humans. Decomposing wood and leaf litter create structures at a microscale on the ground. Each of these patterns provides habitat for different groups of animals and plants.

Patterns also exist within and among species populations. The sex and age ratios of a population affect its reproductive success. It is influenced by its distance from other populations and by the type of habitat between them. For wildlife populations especially, maintaining opportunities to interbreed with other populations strengthens the group as a whole. In addition, varied genetic patterns occur in species, offering different opportunities for adaptation and evolution. Some species consist of populations that are similar across a broad geographic region. Others, with little ability to move and interbreed, exhibit significant genetic variation from one population to the next.

Ecological processes are the third major attribute of ecosystems and determinant of biodiversity. These are the interactions that take place among ecosystem components. Some processes are important because they create the initial conditions that allow species to colonize an area. Other processes maintain an environment conducive to the species’ survival. The types of processes operating in a landscape govern which organisms it can support.

Most people are aware of many large-scale, dramatic processes because the processes affect their lives as well as their landscapes. Severe storms, for instance, produce flooding, landslides, and downed trees. Wildfires threaten homes in addition to burning large forest tracts. Swarms of insect pests leave hillsides of dead trees in their wake. Such landscape “disturbances” create more heterogeneous habitat, which supports a greater range of species.

Ecological processes also include routine, everyday occurrences. An animal seen in the distance might be foraging for plants, preying on other animals, or competing against a similar species. A young animal might be dispersing from its birth site to a new area or in the middle of migration. Seasonal flowers, cones, and shoots signal reproduction and regeneration. These are ongoing activities that maintain individuals, populations, and communities.

Still other processes are difficult to discern, but equally important for sustaining biodiversity. For example, it might take decades for a pond to fill in with reeds and grasses to become a meadow and ultimately a woodland. Similarly, we know that nutrients cycle among plants, animals, soils, water, and the atmosphere, although we cannot see them. A simple stream is shaped by incremental processes such as erosion and sediment deposition. A population long isolated may ultimately become a new species.

In addition to characterizing biodiversity, the three types of ecosystem attributes—components, patterns, and processes—are important for planning because they are interconnected. Each is linked to the others through a myriad of threads. To preserve a rare species, for example, a planner might consider attributes such as habitat area and structure, competing species, land uses, water and vegetation patterns in the landscape, distance between populations, reproductive characteristics, and genetic variations. To reduce nutrient infiltration into a river, the considerations might include width and length of the buffer zone, the types and productivity of buffer vegetation, slope, upland land uses, soils, and waterflow characteristics. Whatever the issue, its solution will involve a range of ecosystem components, patterns, and processes.

Biological Scaling

The next step in developing a framework is to distinguish within the three attribute types. This further organization helps planners identify more aspects of biodiversity and then focus on those particularly relevant to their situation. A useful approach is to think of an area in terms of biological scales. Different levels of biological organization are inherent in any landscape, and each has characteristic components, patterns, and processes.

The concept of a biological hierarchy is common in biology and ecology. It involves a series of levels of structural complexity. Examples of these successive levels include atoms, molecules, cells, tissues, organs, organisms, populations, and communities. Each tier is a composite of those below and is itself nested within the tier above. Distinct properties exist at each scale, such that a given level is more than the sum of its parts.

For planning purposes, we can concentrate on the higher part of the hierarchy, populations and communities, and adapt it to reflect biodiversity concerns. Populations and communities are very useful scales, since they are basic biological units in parks and open spaces. To these we can add landscapes as the tier above communities. Among other components, landscapes are comprised of various communities and exhibit numerous patterns and processes essential to biodiversity. Underneath populations, the fourth tier is genetic. Although genetic diversity is relevant to maintaining populations, it is helpful to isolate it as a separate level as it includes a distinct set of ecosystem attributes (figure 1.3).

The landscape scale involves components and relationships that span large areas. For Mount Diablo, which covers about 30 square miles, either the mountain or the mountain and surrounding region might be considered the “landscape.” Components at this scale include the biotic communities, as well as significant characteristics of them: for example, the proportions in which they occur, their rarity, productivity, and the diversity of species they support. Aspects of hydrology, such as streams, ponds, and springs, are other parts of the landscape. Abiotic components affecting biodiversity include climate, soils, geology, elevation, slope, and aspect. Land uses in and adjacent to the park and past and present management practices also influence the species mix.

Landscape patterns involve the spatial arrangement of components and processes. One type of pattern is the physical aspects of landscape patches. For instance, blue oak woodlands on Mount Diablo can be characterized in terms of their size, shape, or location. A second category includes relationships among different patch types. Communities can be adjacent to or separate from each other or correlated with specific abiotic factors. Recreational areas and campgrounds can be too close to sensitive habitats. The urban/wildland boundary has shifted significantly over the past few decades. A third type of pattern applies to the overall area. For example, the region can be classified in terms of the heterogeneity, or variety, of its vegetation or the degree to which its open space is connected.

Landscape processes produce changes in the components and patterns. Some processes, such as a fire or intense storm, rapidly alter communities. Others result in slow, subtle changes. In the absence of fire, for example, chaparral plants may eventually overrun a grassland. Human land uses are also important processes at the landscape scale. One could examine the degree and rate at which land surrounding Mount Diablo is being developed or the effects of different grazing regimens throughout the park (table 1.1).

The community scale can also be associated with specific components, patterns, and processes. Here, the components include species and key habitat resources. Of particular interest are species that are endangered, rare, limited in distribution, ecologically valuable, or exotic. Tree snags, woody debris, rock outcrops, and perennial streams are examples of important habitat resources on Mount Diablo. Community patterns include characteristics of vegetation structure as well as the distribution of resources. Among the processes operating at this scale are those specifically associated with a vegetation type and those occurring between community organisms. For example, fire is inherent to California’s chaparral, where even without human ignitions it recurs every ten to forty years. When a particular species is the target, a plan might also address community processes such as herbivory, predation, or parasitism.

The salamander ensatina (Ensatina eschscholtzii) is useful for illustrating population and genetic-scale attributes on Mount Diablo, since it is one of the few species on the mountain for which both types of data are available. Stebbins (1954) found approximately 100 ensatinas in an area near Mount Diablo, and estimated that 600 to 700 might occur in an acre of favorable habitat. The size of a population, as well as its density, are population-scale components. Noting overlapping color patterns in ensatina populations throughout California, Stebbins also deduced that individual animals traveled among the populations and interbred. Interbreeding, like reproduction, mortality and population growth, is an example of a population-scale process. Usually, however, the ensatinas moved within a limited oblong area averaging 70 to 135 feet in length. In contrast to most amphibians, ensatinas do not migrate, nor do they depend on water sources to lay their eggs. Their movements appear to be limited to one site. They spend the dry months of the year underground or in leaf litter, emerge aboveground after the first autumn rain, breed in spring, and, as summer arrives, retreat again to moist areas. These types of individual movements constitute population-scale patterns.

Genetic variation in ensatinas was recently studied by Jackman and Wake (1994) and Moritz et al. (1992). In this case, the researchers were not interested in specific genetic components, for example, rare or destructive forms of genes. Their primary focus was on the genetic patterns that characterized the populations and on the number of differences among these patterns. They discovered high levels of variation among populations and greater differences between populations separated by greater geographic distances. These patterns suggested information about genetic processes in ensatinas. For example, since the animals move very little, there is little gene flow among ensatina populations.

By subdividing ecosystem components, patterns, and processes according to biological scales, one can gain a better understanding of a range of aspects of biodiversity. This approach also helps identify attributes from different scales that might influence a specific concern. For example, to conserve a rare community type a planner might consider attributes at the landscape and population levels as well as the community scale. At the landscape level, abiotic factors constrain where vegetation grows, land-use pressures affect the rate at which it is developed, large-scale disturbances influence species diversity, and vegetation patterns govern the movements of community animals. At the population level, characteristics of regeneration, demographics, and movement affect the species and processes of the community. In general, diversity at any given level will be constrained by attributes associated with the level above and will exhibit properties that can be explained in part by the level below. Because of these interactions, it is useful to consider and plan for biodiversity at multiple scales.

(Continues…)Excerpted from Planning for Biodiversity by Sheila Peck. Copyright © 1998 Sheila Peck. Excerpted by permission of ISLAND PRESS.
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