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Conserving Forest Biodiversity
A Comprehensive Multiscaled Approach
By David B. Lindenmayer, Jerry F. Franklin ISLAND PRESS
Copyright © 2002 David B. Lindenmayer and Jerry F. Franklin
All rights reserved.
ISBN: 978-1-59726-853-0
CHAPTER 1
Critical Roles for the Matrix
The days are over when the forest may be viewed only as trees and the trees viewed only as timber. —U.S. SENATOR HUBERT HUMPHREY (IN PATTON 1992)
The conservation of biodiversity is one of the fundamental guiding principles for ecologically sustainable forest management. Many existing conservation programs are limited to a primary or exclusive focus on lands contained in reserves for biodiversity conservation. Yet, most forest will be in off-reserve, or matrix, lands in the vast majority of forest regions and forest types. Comprehensive strategies for the conservation of forest biodiversity must include both reserves and matrix-based strategies. The importance of the matrix for the conservation of biodiversity in forests reflects its dominance in both temperate and tropical regions—most forest landscapes have been, or will be, actively used and managed. Therefore, many forest-dependent species will occur primarily in matrix !ands—or not at all.
How the matrix is managed will influence the size and viability of populations of many forest taxa and thus biodiversity per se. Matrix conditions also greatly influence connectivity between reserves and the movement of organisms. In addition, by acting as buffers, matrix conditions strongly control reserve effectiveness. The matrix must sustain functionally viable populations of organisms that are fundamental to the maintenance of essential ecosystem processes such as nutrient cycling, seed dispersal, and plant pollination—processes that underpin the long-term productivity of ecosystems and their ability to produce goods and services for human use.
The conservation of biodiversity has become a major concern for resource managers and conservationists worldwide, and it is one of the foundation principles of ecologically sustainable forestry (Carey and Curtis 1996; Hunter 1999). This represents a major challenge for forest management because forests support approximately 65 percent of the world's terrestrial taxa (World Commission on Forests and Sustainable Development 1999). They are the most species-rich environments on the planet, not only for vertebrates, such as birds (Gill 1995), but also for invertebrates (Erwin 1982; Majer et al. 1994) and microbes (Torsvik et al. 1990).
Setting aside networks of dedicated reserves has been the traditional approach advocated by many conservation biologists to conserve the extraordinary biodiversity that characterizes forest ecosystems. Many books and vast numbers of scientific articles have been written on reserve design and selection (Shafer 1990; Noss and Cooperrider 1994; Margules et al. 1995; Anonymous 1996; Pigram and Sundell 1997). In this book, we argue that the conservation of a significant proportion of the world's forest biodiversity will require a far more comprehensive and multiscaled approach than simply partitioning forest lands into reserves and production areas, which we term the matrix. This book attempts to lay the foundations for such a comprehensive strategy. Although large ecological reserves are discussed (see Chapter 5), most of this book addresses management of the matrix.
Most temperate and subtropical forest landscapes are composed primarily (or even exclusively) of off-reserve forests, or matrix lands. It has been estimated that between 90 and 95 percent of the world's forests have no formal protection (Sugal 1997). This is particularly true in temperate regions where the most productive (and species-diverse) forested lands have already been extensively modified by humans (Franklin 1988; Virkkala et al. 1994). Therefore, forests outside reserves are extremely important for the conservation of biodiversity—how they are managed will ultimately determine the fate of much biodiversity.
Our primary objective in this book is to illustrate the importance of the matrix for biodiversity conservation and to propose strategies for enhanced matrix management that can be the basis for a comprehensive approach to maintaining forest biodiversity. We begin in this first chapter by providing our definitions of biodiversity and the matrix. We then illustrate the importance of the matrix for conserving forest biodiversity.
Defining Biodiversity and Ecologically Sustainable Forest Management
There are many definitions of biodiversity. Ours is relatively simple:
Biodiversity encompasses genes, individuals, demes, metapopulations, populations, species, communities, ecosystems, and the interactions between these entities.
There are also many interpretations of ecologically sustainable forest management (Amaranthus 1997). Ours follows Lindenmayer and Recher (1998):
Ecologically sustainable forest management perpetuates ecosystem integrity while continuing to provide wood and non-wood values; where ecosystem integrity means the maintenance of forest structure, species composition, and the rate of ecological processes and functions with the bounds of normal disturbance regimes.
Two other terms widely used in this book are stands and landscapes. We define a stand as "a patch of forest distinct in composition or structure or both from adjacent areas."
This definition is often inadequate, such as when modified cutting practices like retention at the time of harvest are employed (see Chapter 8); this means that stands can actually be composed of structural mosaics (Franklin et al. 2002). However, the simple definition is widely used and understood (see Helms 1998) and, except where noted, we use it in this book.
Given that the focus of this book is on forests, we crudely define a landscape as "many sets of stands," or patches, that cover an area ranging from many hundreds to tens of thousands of hectares. Drainage basins are a good landscape unit, but it often is necessary to consider much smaller areas or very large regional landscape units.
Defining the Matrix from a Conservation Biology and Landscape Ecology Perspective
In the technical language of landscape ecology, the matrix is defined as the dominant and most extensive "patch type" (Forman 1995; Crow and Gustafson 1997). Other criteria used in its definition include the portion of the landscape that is best connected and that has a controlling influence over key ecosystem processes such as water and energy flows (Forman 1995).
In conservation biology and forest planning literature, the "matrix" often refers to areas that are not devoted primarily to nature conservation. In temperate regions in particular, these areas are generally available for resource extraction and use, including the production of commodities, as well as for many other human uses. The definitions of "matrix" from both landscape ecology and conservation biology perspectives are congruent in many temperate regions where reserved lands are clearly in the minority. Conversely, in undeveloped regions, the matrix sensu landscape ecology (the dominant patch type) may not be equivalent to the matrix sensu conservation biology because the majority of the forested land is in a "natural" condition. For this book, we have adopted a very broad definition of the matrix:
The matrix comprises landscape areas that are not designated primarily for conservation of natural ecosystems, ecological processes, and biodiversity regardless of their current condition (i.e., whether natural or developed).
Much of our focus is on biodiversity conservation in wood production areas outside the dedicated reserve system because land allocation in many jurisdictions around the world has created a distinction between reserves and commodity landscapes. The term matrix management is used frequently throughout the book, and it refers to approaches to conserve biodiversity in forests outside the reserve system.
Critical Roles for the Matrix
There are four critical roles the matrix plays that relate specifically to biodiversity conservation: (1) supporting populations of species, (2) regulating the movement of organisms, (3) buffering sensitive areas and reserves, and (4) maintaining the integrity of aquatic systems.
Conditions in the matrix will determine the degree to which it contributes positively or negatively to these roles.
Conserving biodiversity for its own sake is only one of many possible goals of matrix management. Another is the production of commodities, such as wood, and services, such as well-regulated flows of high-quality water. Management practices in the matrix will determine whether these goods and services can be sustained, because such practices also influence whether elements of biodiversity critical to long-term sustainability, such as mycorrhizal-forming fungi, are maintained (Perry 1994). Such organisms need to be conserved at functionally effective levels to maintain ecosystem processes (Conner 1988). Hence, conservation of biodiversity in the matrix is fundamental to achieving intrinsic goals (e.g., sustainable production of wood products) and extrinsic goals (e.g., maintenance of regional biodiversity and regulation of stream-flow).
Supporting Populations of Species
The matrix can be managed to support broadly distributed populations of many species (deMaynadier and Hunter 1995) (Figure 1.1). Such populations have a lower risk of extinction through demographic stochasticity (Pimm et al. 1988; McCarthy et al. 1994) and environmental variability (Thomas 1990; Tscharntke 1992) (Figure 1.2). Large populations also have greater levels of genetic variation (e.g., Billington 1991; Madsen et al. 1999b) and are less likely to suffer extinction as a result of genetic stochasticity (Lacy 1987, 1993a; Young et al. 1996) (Figure 1.3). For example, Saccheri et al. (1998) demonstrated that low levels of genetic variation and subsequent inbreeding depression significantly increased the risk of extinction of fragmented populations of the Glanville fritillary butterfly (Melitaea cinixia) in Finland.
The maintenance of large, well-distributed populations also reduces the risks that an entire population will be extinguished in a single catastrophic event such as a wildfire (Gilpin 1987; McCarthy and Lindenmayer 1999a). In the forests of southeastern Australia, the maintenance of populations of Leadbeater's possum (Gymnobelideus leadbeateri) in many habitat patches is predicted to reduce extinction risks as a result of wildfire (Lindenmayer and Possingham 1995a).
Maintaining populations of species in the matrix can supplement populations in reserves. Species that persist in the matrix will also be those most likely to reside in reserves or remnant patches (Diamond et al. 1987; Laurance 1991a; As 1999; Renjifo 2001). The contribution of matrix populations to the persistence of populations within reserves is illustrated by the bald eagle (Haliaeetus leucocephalus) in Yellowstone National Park. Although Yellowstone is a large reserve (more than 1 million hectares), the long-term persistence of the species within the park is dependent on dispersal by animals from off-reserve populations (Swenson et al. 1986) (Figure 1.4).
Evidence of rapid species turnover within protected areas (e.g., Margules et al. 1994a) also suggests that individuals dispersing from populations in the matrix can help reverse localized extinctions within reserves (Thomas et al. 1992a; Hanski et al. 1995). Many studies show that the occupancy of reserves and habitat patches by biota is strongly related to their abundance at larger spatial scales (i.e., throughout regions) (e.g., Askins and Philbrick 1987; Askins et al. 1987; Freemark and Collins 1992; McGarigal and McComb 1995; Schmiegelow et al. 1997; Arnold and Weeldenburg 1998; Boulinier et al. 2001).
Regulating the Movement of Organisms
The matrix has a significant effect on connectivity in forest landscapes (Figure 1.5). In most temperate forest landscapes, the matrix will be the most important factor influencing connectivity—the movement of organisms and genes will be either facilitated or obstructed by the conditions in the matrix (Taylor et al. 1993).
Noss (1991) defined connectivity as "linkages of habitats ... communities and ecological processes at multiple spatial and temporal scales."
Connectivity in forest landscapes embodies concepts such as
• Persistence of species in cutover areas
• Species recolonization of cutover areas
• Exchange of individuals and genes among subpopulations in a metapopulation
• The role of suboptimal habitat (which may or may not be logged) in maintaining links with optimal habitat for particular species
Facilitating connectivity in the matrix may prevent populations of species in rese+ves from becoming isolated and fragmented (Burkey 1989). It also can allow populations to maintain or increase their demographic and genetic size (Lacy 1993a; Saccheri et al. 1998), thereby enhancing chances of long-term persistence (Scotts 1994). Connectivity is also important because of the role of movement in shaping distribution and abundance patterns (Stenseth and Lidicker 1992)—it underpins processes such as localized extinction and recolonization dynamics (Brown and Kodric-Brown 1977) and influences patterns of gene flow (Leung et al. 1993; Mills and Allendorf 1996).
For plants, connectivity may include not only movements of species and populations, but also the movement of propagules such as spores, pollen, and seeds. In the case of animals, connectivity involves five broad types of movement (modified from Hunter 1994):
1. Day-to-day movements, such as those within home ranges or territories. These can be small for species such as adult frogs, or large in the case of wide-ranging animals like bats (e.g., Lumsden et al. 1994) or large vertebrates like the black bear (Ursus americanus; Klenner and Kroeker 1990).
2. Dispersal events between the natal territory and suitable habitat patches (Wolfenbarger 1946). These are typically made by juvenile or sub-adult animals attempting to establish new territories (Stenseth and Lidicker 1992).
3. Annual patterns of long-distance migration, which can span continents and/or hemispheres (Keast 1968; Flather and Sauer 1996).
4. Nomadic movements made in response to temporal and spatial variability of important resources (e.g., food; Price 1999).
5. Large shifts in distribution patterns in response to climate change. These have typically been slow in the past (Keast 1981), but more-rapid and extreme changes are expected in response to global climate change (Peters and Lovejoy 1992; see Chapter 5).
Connectivity is controlled by conditions such as appropriate vegetation cover or key structures (e.g., logs) in the matrix. Connectivity relates, in part, to the extent of matrix hostility, or "permeability," for movement (Wiens 1997a; Hokit et al. 1999). Matrix hostility and an associated lack of connectivity may result in suitable habitat remaining unoccupied, meaning that the spatial distribution of a species may not directly correspond to the spatial distribution of available habitat (Wiens et al. 1997). The connectivity role of the matrix is illustrated by a lack of gap-crossing ability among some forest birds (Dale et al. 1994; Desrochers and Hannon 1997), resulting in habitat fragmentation. The reluctance of some species of forest birds to move through open areas has been documented in many studies (e.g., Martin and Karr 1986; van Dorp and Opdam 1987; Bierregaard et al. 1992). Conversely, fragmentation-tolerant species will typically be those that can readily cross matrix lands and colonize isolated patches (Villard and Taylor 1994; Robinson 1999).
A matrix that provides a high degree of connectivity is critical, because habitat loss and habitat fragmentation are major contributors to biodiversity loss (Wilcove et al. 1986; Groombridge 1992). For example, Angermeier (1995) showed that a lack of connectivity contributed to extinction proneness in fish. Because natural forest landscapes are typically characterized by high levels of connectivity (Noss 1987; Lindenmayer 1998), the connectivity role of the matrix assumes even greater importance. Species that were abundant and well distributed in such well-connected landscapes may not have evolved well-developed dispersal mechanisms. Such taxa with relatively low mobility may be vulnerable to landscape change and fragmentation because their dispersal systems are maladapted to reduced levels of connectivity.
(Continues...)
Excerpted from Conserving Forest Biodiversity by David B. Lindenmayer, Jerry F. Franklin. Copyright © 2002 David B. Lindenmayer and Jerry F. Franklin. Excerpted by permission of ISLAND PRESS.
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