Overstory #231 - Biodiversity: ten strategies for commodity production landscapes
Biodiversity conservation in forestry and agricultural landscapes is important because (1) reserves alone will not protect biodiversity; (2) commodity production relies on vital services provided by biodiversity; and (3) biodiversity enhances resilience, or a system’s capacity to recover from external pressures such as droughts or management mistakes. We suggest ten guiding principles to help maintain biodiversity, ecosystem function, and resilience in production landscapes. Landscapes should include structurally characteristic patches of native vegetation, corridors and stepping stones between them, a structurally complex matrix, and buffers around sensitive areas. Management should maintain a diversity of species within and across functional groups. Highly focused management actions may be required to maintain keystone species and threatened species, and to control invasive species. These guiding principles provide a scientifically defensible starting point for the integration of conservation and production, which is urgently required from both an ecological and a long-term economic perspective.
Only about 12% of Earth’s land is located in protected areas, and less than half of this is managed primarily for biodiversity conservation (Hoekstra et al. 2005). Although protected areas are an essential part of any credible conservation strategy (Margules and Pressey 2000), it is becoming increasingly clear that reserves alone will not protect biodiversity because they are too few, too isolated, too static, and not always safe from over-exploitation (Liu et al. 2001; Bengtsson et al. 2003; Rodrigues et al. 2004). For these reasons, it is now widely recognized that conservation within protected areas needs to be complemented by conservation outside protected areas (Daily 2001; Lindenmayer and Franklin 2002).
Production industries like agriculture and forestry dominate human land use (Morris 1995). These industries directly depend on a range of vital ecosystem services, such as healthy soils, nutrient cycling, and waste decomposition (Daily 1997). The diversity of genes, species, and ecological processes makes a vital contribution to ecosystem services. For example, biodiversity provides important pollinators, seed dispersers, and pest control agents on which agriculture and forestry depend (Daily 1999). More generally, by providing multiple species that fulfill similar functions but have different responses to human landscape modification, biodiversity enhances the resilience of ecosystems (Walker 1995). Such response diversity “insures the system against the failure of management actions and policies based on incomplete understanding” (Elmqvist et al. 2003). Maintaining biodiversity in production landscapes therefore often constitutes an economically profitable synergy between conservation and production (Daily 1997; Ricketts et al. 2004).
Pattern-oriented management strategies
Strategy 1: Maintain and create large, structurally complex patches of native vegetation
The species–area curve is one of a few general principles in ecology (McGuinness 1984). Other things being equal, larger patches tend to support more species than smaller patches. In addition to its area, the structure of a given patch of native vegetation is fundamentally important for biodiversity. Again, other factors being equal, structurally characteristic and complex vegetation tends to support higher biodiversity than structurally simple or degraded vegetation (MacArthur and MacArthur 1961). Some structural elements are particularly important because a large number of species and ecological processes rely on them. What constitutes such “keystone structures” varies between ecosystems, and can include a wide range of structural features, ranging from ephemeral water bodies in recently plowed German agricultural fields (Tews et al. 2004) to tree hollows in Australian woodlands and forests (Gibbons and Lindenmayer 2002).
Strategy 2: Maintain structural complexity throughout the landscape
The area surrounding patches of native vegetation is often termed the “matrix” (Forman 1995). The matrix is the dominant landscape element, and exerts an important influence on ecosystem function. A matrix that has a similar vegetation structure to patches of native vegetation (ie that has a low contrast) will supply numerous benefits to ecosystem functioning. Three key benefits of a structurally complex matrix are the provision of habitat for some native species, enhanced landscape connectivity, and reduced edge effects.
Strategy 3: Create buffers around sensitive areas
As outlined in Strategy 2, a structurally complex matrix can mitigate some of the negative impacts of edge effects on biodiversity. An alternative, and not mutually exclusive, strategy is to specifically create buffers around patches of native vegetation. These can help to lessen negative edge effects, for example by “sealing off” vegetation patches from strongly altered conditions in the matrix (Noss and Harris 1986).
Strategy 4: Maintain or create corridors and stepping stones
A structurally complex matrix can contribute to the connectivity of habitat patches for some species, and may enhance the connectivity of some ecological processes (Strategy 2). A complementary strategy to enhance landscape connectivity is to create or maintain corridors and stepping stones between large patches of native vegetation. Corridors are elongated strips of vegetation that link patches of native vegetation; stepping stones are small patches of vegetation scattered throughout the landscape (Forman 1995).
Strategy 5: Maintain landscape heterogeneity and capture environmental gradients
From the perspective of biodiversity conservation, vast areas of unmodified land are likely to be optimal. Representative areas of “wilderness” are key to biodiversity conservation and such areas should be protected in nature reserves (Margules and Pressey 2000). However, where humans do use landscapes for the production of agricultural or forestry commodities, there is widespread evidence that heterogeneous landscapes, which resemble natural patterns, provide greater biodi- versity benefits than intensively managed monocultures.
Summary of pattern-oriented management strategies
Implementation of the five pattern-oriented strategies suggested above will result in heterogeneous production landscapes, with large and structurally complex patches of native vegetation scattered throughout. These patches will be connected by corridors and stepping stones, and will be situated within a matrix that attempts to retain structural characteristics similar to those of native vegetation. The resulting production landscapes are likely to sustain higher levels of biodiversity and will be more resilient to external shocks (such as drought) than more simplified systems. Notably, determining the appropriate mix of management strategies, and which ones are likely to be particularly important, depends on the ecosystem in question, its species, and current landscape patterns. Further safeguards for biodiversity, ecosystem function, and resilience may be achieved by implementing the five additional, processoriented management strategies set out below.
Process-oriented management strategies
Strategy 6: Maintain key species interactions and functional diversity
Human landscape modification for commodity production alters the composition of ecological communities. This changes species interactions such as competition, predation, and mutualist associations (Soulé et al. 2005). Two approaches focusing on species interactions may protect important ecosystem functions. The first is conserving keystone species; the second is maintaining species diversity within functional groups.
Strategy 7: Apply appropriate disturbance regimes
Landscape change often results in a change to historical disturbance regimes. Such changes can substantially alter vegetation structure and species composition (Hobbs and Huenneke 1992), and may trigger cascades that cause fundamental and potentially irreversible changes to ecosystems (Hobbs 2001). Pronounced ecological changes in production landscapes can result from changed fire regimes (including intensity, frequency, and spatial extent), changed grazing regimes, and logging (Hobbs 2001; Lindenmayer and Franklin 2002; Bowman et al. 2004). Understanding the impacts that particular disturbance regimes have on ecosystem functioning is therefore important for ecosystem management. Broadly speaking, disturbance regimes that attempt to mirror historical ones are probably a useful starting point for management (Lindenmayer and Franklin 2002; Bowman et al. 2004).
Strategy 8: Control aggressive, over-abundant, and invasive species
Landscape change for commodity production tends to result in habitat loss for many species. However, it also often strongly favors a small number of native or introduced species. Some of the species which benefit from anthropogenic landscape change can become overly abundant, and may negatively affect other species through aggressive behavior, competition, or predation. For example, in southeastern Australia, widespread land clearing for agriculture has led to expanded populations of the noisy miner (Manorina melanocephala). The native but highly aggressive honeyeater out-competes many other native birds. The resulting decline in insectivorous birds has, in turn, been linked to insect outbreaks and reduced tree health in many agricultural landscapes (eg Grey et al. 1998).
Strategy 9: Minimize threatening ecosystem-specific processes
Although agriculture and forestry can threaten biodiversity, they are by no means the only threats; a range of other processes can be equally or more important in some landscapes. Examples include chemical pollution (Oaks et al. 2004) and hunting by humans (Reynolds 2003). Such ecosystemspecific threats need to be considered in the management of biodiversity in production landscapes, and situation-specific action taken to mitigate them.
Strategy 10: Maintain species of particular concern
The above guidelines have focused on maintaining biodiversity in general, and functional groups in particular, with the aim of maintaining ecosystem resilience. These approaches are likely to benefit a number of different species. However, some species may still “fall through the cracks” (Hunter 2005). Unless they are keystone species, highly threatened species are often very rare, and may contribute lit- tle to overall ecosystem function (Sekercioglu et al. 2004). Nevertheless, maintaining such species should still be an important priority because once extinct, their decline cannot be reversed. The management of threatened species has a long history in conservation biology, and highly focused case-specific recovery plans are often needed to mitigate the decline of particular species (Caughley and Gunn 1996). Determining the potential presence of rare or threatened species is an important first step in maintaining species of particular concern.
Summary of process-oriented management strategies
The process-oriented strategies listed here focus on the maintenance of desirable species (keystone species, threatened species), and the control of undesirable ones (invasive species). In addition, disturbance regimes are most likely to maintain biodiversity if they mirror historical disturbance regimes. Highly specific threats such as hunting or pollution need to be considered on a case by case basis.
How do these strategies help in practice?
Management approaches that solve all ecological and economic problems at once do not exist and the strategies suggested in this paper are therefore general. Generality, by necessity, comes at a cost – the loss of precise details. This means that the strategies outlined above do not amount to a prescriptive list of management actions that will solve all conservation problems in all production landscapes. Nevertheless, we believe that they provide a useful conceptual basis for maintaining biodiversity, ecosystem function, and ecosystem resilience in production landscapes. In fact, the first principles for the design of nature reserves were also broad and non-quantitative. Yet, in the 30 years since Diamond (1975) suggested these general principles, sophisticated algorithms have been developed that take into consideration the size, representativeness, and complementarity of nature reserves (Margules and Pressey 2000). We argue that the successful integration of conservation and production will be at least equally important to halting the current biodiversity crisis as will widely agreed upon targets to protect some of Earth’s land in formal nature reserves (Rodrigues et al. 2004). Moreover, biodiversity in production landscapes is fundamental to ecosystem functioning, which ultimately provides the basis not only for biodiversity conservation but also for the continued production of marketable commodities (Daily 1997). The ten guiding principles are put forward here as working hypotheses, to be refined by the scientific community over time. A key challenge for future work will be to further elucidate the trade-offs and potential inconsistencies between different management strategies, both from an ecological and financial perspective. Future work may be most effective if it is interdisciplinary and considers both conservation and production objectives.
The strategies described above provide a basis for the integration of conservation and production. The details of how large patches need to be, or which introduced species should be controlled, need to be established on a case by case basis.
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This article was excerpted with the kind permission of the authors and publisher from:
Fischer, Joern, David B. Lindenmayer, and Adrian D. Manning. 2006. Biodiversity, ecosystem function, and resilience: ten guiding principles for commodity production landscapes. Frontiers in Ecology and the Environment 4: 80–86. © The Ecological Society of America
About the Authors
Joern Fischer, David B Lindenmayer, and Adrian D Manning, Centre for Resource and Environmental Studies, The Australian National University, Canberra, ACT 0200, Australia (Contact: email@example.com)
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