Alan R. Pierce and Jamison B. Ervin are with the Forest Stewardship Council US in Waterbury, Vermont, USA.
How certification agencies have addressed landscape ecology tenets to date, opportunities and limitations to future development.
In the past five years, independent certification has gained momentum as a potentially effective mechanism to improve the management of forests (Viana et al., 1996). Certification programmes audit the field practices and management systems of forestry operations, award certificates to managers who meet forest management standards and verify the tracking of products from well-managed forests to consumers (Ervin et al., 1996; Cabarle et al., 1995). A certification label thus enables consumers to differentiate between forest products in the marketplace on the basis of the ecological and social aspects of production.
Certification was developed as a voluntary policy tool for individual forest management units. Some authors have suggested that certification may be a limited forest policy tool because it largely fails to consider landscape and ecosystem considerations within and beyond the boundaries of individual parcels (e.g. Noss, 1998; Dudley, Elliott and Stolton, 1997; O'Hara et al., 1994). This article explores how independent forest management certification could incorporate certain aspects of landscape ecology and identifies others that certification cannot address. Examples in this paper are given from a United States perspective. In countries with differing land tenure patterns, forest policies, forest uses, forest history and cultural values, the ability to integrate landscape issues with forest management certification may vary considerably.
While the term "landscape ecology" has existed for decades, its maturity into a distinct scientific discipline is largely a recent phenomenon (Forman, 1995). Although still an emerging science, landscape ecology is rapidly developing a core set of concepts, themes and principles, including:
· landscape structure and function (Dramstad, Olson and Forman, 1996; Forman, 1995; Risser, 1987; Forman and Godron, 1986);
· landscape change, flux, stability and disturbance (Turner, Gardner and O'Neill, 1995; Forman, 1995; Risser, 1987; Forman and Godron, 1986; Risser, Karr and Forman, 1984);
· spatial and temporal scales (Dramstad, Olson and Forman, 1996; Forman, 1995; Turner, Gardner and O'Neill, 1995; Urban, O'Neill and Shugart, 1987; Risser, Karr and Forman, 1984);
· landscape ecology as a framework for natural resource management planning (Dramstad, Olson and Forman, 1996; Forman, 1995; Risser, Karr and Forman, 1984).
ELEMENTS OF LANDSCAPE ECOLOGY THAT CERTIFICATION COULD INCORPORATE
This section explores aspects of landscape ecology that certification programmes could incorporate. It considers programmes that currently include some of the elements and provides suggestions where additional consideration of landscape ecology principles may be appropriate.
Certification and landscape structure and function
Landscape structure refers to the spatial arrangement and juxtaposition of landscape elements within the surrounding matrix. Such elements include forested patches, roads and waterways (Dramstad, Olson and Forman, 1996). Landscape function refers to both the interrelation between biota and structure (e.g. migration corridors, feeding grounds, wintering yards) and the movement of materials, water, wind and energy through the structure (Dramstad, Olson and Forman, 1996; Forman and Godron, 1986). Certification programmes address four landscape ecology concepts relating to forest structure and function: forest fragmentation, connectivity, patch size, and protection of species at risk.
Fragmentation, or the splitting and isolation of habitats, can pose a major threat to the biodiversity contained in forest ecosystems (Wilcox and Murphy, 1985). Landscape elements that maintain connectivity, and thus enhance landscape structure and function, include large patches, corridors and stepping stones. Large intact patches, such as large roadless areas and protected reserves, may serve as refugia and maintain important habitat for numerous species, particularly forest interior species (e.g. thrushes) and wide-ranging carnivores (e.g. bears and wolves). Stepping stones and corridors maintain connectivity between forested patches and facilitate the spatial flow of animals and genetic material within the matrix.
Some current certification programmes address forest fragmentation, connectivity within the landscape and the establishment of ecological reserves. The following are excerpts from certification standards:
"Stand size diversity is designed to avoid fragmentation caused by a preponderance of uniformly sized stands. The extent and effectiveness of connectivity between late seral stage areas are considered in management plans and incorporated in practice."
"The movement of plant and animal species between reserved and harvested areas should be maintained by retaining corridors of uncut forest based on streamsides with links up slopes and across ridges to connect adjoining catchments, connecting any large patches of forest which will not be harvested."
(Soil Association, 1994)
"Design and layout of reserves or special management zones is considered at the watershed and landscape levels. Connectivity of forested areas should be considered in planning of reserves or special management zones."
Several recent certifications include compliance with basic landscape ecology principles as conditions for future maintenance of the certificate. When Scientific Certification Systems (SCS) certified 485 000 ha of Pennsylvania's Bureau of Forestry lands in 1997, conditions for retention of the certificate stipulated that:
"Within three years the Bureau of Forest (BOP) will develop a formal, comprehensive plan for addressing landscape-level issues including forest fragmentation and connectivity that addresses dissection, perforation and corridors......The BOF should develop and implement an ecological reserve program based upon ecological analysis and conservation biology principles. Its components will include the establishment of large ecological reserves, a matrix of smaller reserves within the managed forest, and a system of corridors connecting them as part of a comprehensive plan to maintain connectivity and areas of high biodiversity."
Applying landscape ecology principles as part of a certification assessment presents novel challenges. Landscape-level issues such as forest fragmentation, patch size and connectivity may not be as readily discernible to a forest certification assessment team as stand-level issues such as post-harvest damage, stocking levels and soil erosion. Certified forest owners and certification teams already use aerial photographs to assess forest types and inventories. More sophisticated landscape-scale planning tools, such as satellite imagery, GPS units and geographic information systems (GIS), are also employed by certified operations and companies interested in applying for certification in the future (Corbley, 1998). Such tools can provide valuable information about landscape patchiness, animal corridors and the fragmentary effects of road layout on the landscape, thereby contributing to a landscape perspective in forest planning, management, monitoring and certification.
An important landscape element to consider in forest management is patch size. An example of a certifier standard encompassing patch size is: "Stands are managed with an ecological landscape-scale perspective where landscape spatial patterns and considerations influence the layout and temporal patterns of harvest units".
"Patch size", according to Franklin and Forman (1987), "is of central importance in many fields including considerations of biological diversity, nature reserve design and logging operations." These authors employed a chequerboard model system, based on current clear-cutting practices employed in the western United States, to analyse the ecological impacts of timber harvesting on landscape structure in the Pacific Northwest Douglas fir region. In a hypothetical 1 000 ha landscape divided into 10 ha patch cuts, the authors found that "at about the 30 percent cut-over point, the average forest patch size begins to drop sharply because cuts coalesce into continuous lines of patches dividing the previously continuous forest into sections." Certifiers and forest managers could improve their evaluations of landscape ecology criteria by considering the implications of modelling exercises such as Franklin and Forman's when evaluating the impact of harvesting patterns on forest structure and function in the United States Pacific Northwest. Certifiers could also seek analogous examples of modelling programmes for different forest types and silvicultural practices in other regions of the globe.
Patch size may influence temporal use of forests by mammals and migrant birds. Bird studies in particular have provided good examples of the inherent complexities involving biota-forest interactions. Robinson et al. (1995) and McIntyre (1995) concluded that forest patch size determines bird use and bird diversity in forests, with larger patches generally supporting higher avian diversity and greater numbers of interior species. Robinson et al. also found that fragmentation of forest patches leads to declines in the nesting success of certain species of migrant songbirds. While certifier standards address the overall maintenance of forest ecosystem conditions and processes, specific standards addressing patch size and shape after harvest have not been well defined.
Certain structural and functional elements determine a landscape's ability to support and maintain species at risk. Such species include: those that require large areas (e.g. forest carnivores such as grizzly bears); species that are dispersal-limited (e.g. flightless insects, small mammals and animals prone to road kill); species limited by availability of critical resources for feeding and breeding; species influenced by processes such as wind, fire, flooding and competition with exotic species; narrowly endemic species; and keystone species whose presence or activities have a large impact on their surrounding environment (Noss, 1998).
Certifiers address some aspects of landscape elements and processes that maintain and protect species at risk. Examples include:
"No entry' areas and times are established for particular wildlife species."
"Landowners consider prudent reintroduction of fire into the forest ecosystem; management activities mimic the effects of periodic wildfires; stand conditions are not dominated by the effects of fire exclusion."
"Conservation of threatened, rare, endangered and unusual plant and animal species, natural communities and critical habitats, are explicitly incorporated into management and harvesting plans."
Certification and forest change, flux, stability and disturbance
Change and flux address "the dynamics or alteration in spatial pattern and functioning over time" (Dramstad, Olson and Forman, 1996, p. 14) in a landscape, while stability refers to a landscape's plasticity and resilience, i.e. its ability to resist change and recover quickly from disturbances (Forman and Godron, 1986). "Disturbance" includes events that strongly influence natural patterns, processes and biodiversity across landscapes (Turner, Gardner and O'Neill, 1995), including those caused by humans, and natural phenomena such as floods, fires, insect outbreaks and tornadoes. Certification addresses three landscape ecology concepts related to forest change, flux, stability and disturbance: increased forest stability through longer rotations; seral-stage diversity; and management of insect outbreaks, exotic species and large-scale disturbances.
Human settlement, agriculture and timber harvesting have led to the elimination of most of the old-growth stands across the continental United States, resulting in altered spatial patterns, stability and functions in United States forests. Certification standards often cite the importance of restoration activities that counteract human impacts on the landscape and lead to increased biodiversity, improved forest resilience and the creation of a variety of seral stages. In general, certification organizations embrace the principle of longer rotations, a philosophy that the Society of American Foresters' task force on ecosystem management also cited as integral to achieving long-term, ecologically sensitive forestry in the United States (SAP, 1993). SCS (1995) uses the following standard to evaluate the restoration of seral-stage diversity:
"The vegetative species and habitats found within the ownership are similar to pre-settlement distributions, to the extent that landowner actions and policies have had or can have an influence on species and habitat conditions, over time. Where possible, species composition is restored to native/natural conditions."
Different species use and require different habitats and seral stages within forest ecosystems (Beattie, Thompson and Levine, 1993). Certification standards encourage a diversity of seral stages to provide a variety of habitats and resilience within the forest system, while aiming at increasing overall biodiversity:
"Across the ownership and the landscape in which it is located, management actions lead to an optimal distribution of seral stages from early regeneration to post-mature/senescent stands (i.e. 'old-growth'), both in total acreage and geographic dispersion."
Judging the appropriate scale and temporal frequency of harvesting practices on individual ownerships within the larger context of historical change, flux, stability and disturbance of forests at the landscape level remains a challenge for certification teams. As Turner, Gardner and O'Neill (1995) posit: "Disturbance dynamics play an important role in determining community structure - and hence biodiversity."
Examples of how certifiers address potential disruption to the stability and resilience of forest systems posed by the introduction of exotic species include:
"Use of exotic species is carefully controlled and actively monitored such that adverse ecological impacts are avoided."
"Management activities reduce risks from invasion or expansion of exotic species in the forest."
Certification and spatial and temporal scales of forest management
Scale encompasses both spatial hierarchies, such as the interaction between forest stand, watershed and landscape levels (Turner, Gardner and O'Neill, 1995), and temporal patterns, such as the interaction between daily, seasonal, annual and successional cycles.
As noted earlier, Franklin and Forman's (1987) chequerboard model found that fragmentation of Douglas fir forests begins when 30 percent of the forest is cut over. For these authors, it was clear "that ecological consequences can differ drastically depending on the pattern imposed on a landscape by land-use activities." The temporal and spatial aspects of timber harvesting produce long-term effects on landscapes, forest structure and function and species composition. To counteract fragmentation, Franklin and Forman recommend that land managers employ "progressive or clustered cuts from scattered nuclei" (appropriate to management objectives and landscape characteristics) and create reserve areas of undisturbed forest.
Earlier certifier standards touched on the creation of reserves and connectivity within the landscape. Examples of standards that address the temporal and spatial scale of harvesting include:
"Stands are managed with an ecological landscape-scale perspective where landscape spatial patterns and consideration influence the layout and temporal patterns of harvest units."
"Management addresses the diversity, composition and structure of the forest at the stand, watershed and landscape levels."
Spatial scale is particularly important because it applies to the size of the forest management unit being certified. The ability of owners of small forest holdings to address large-scale landscape issues is limited. For example, a non-industrial private land-holding of less than 100 acres (40.5 ha) might be able to address microscale wildlife-related standards, such as:
"Management practices address the retention of cavity, den and/or snag trees for wildlife habitat."
"River and stream corridors, steep slopes, fragile soils, wetlands, vernal pools, lake and pond shorelines, and other hydrologically sensitive areas are automatically designated as special management zones."
Larger landowners can be expected to follow similar standards. However, while small landowners may only be able to protect snags, rare and endangered species and vernal pools, larger landowners may also be expected to contribute towards the maintenance of wildlife corridors and the creation of large reserve areas and to consider the long-term effects of harvesting patterns on the landscape. To determine whether higher expectations could be held for small certified landholdings, it may be worthwhile for certifiers to explore what Urban, O'Neill and Shugart (1987) term "prescriptive scaling", where wider landscape processes (e.g. fire) are rescaled to small patches with the aim of moving ecological dynamics towards equilibrium.
Monitoring is a key requirement under independent certification systems. Certifier expectations for monitoring systems differ from small landholdings to large landholdings owing to unequal access to technical expertise, variance in intensity of management and disparity in the availability of human and financial resources. As Turner (1989) and Short and Hestbeck (1995) note, monitoring needs to occur at a variety of scales to supply the information and perspective needed on specialist species, critical habitat, mortality, recruitment, and landscape-scale pattern and process.
Certification and natural resource planning
Landscape ecology as a planning framework encompasses the application of scientific principles to disciplines such as forest management, land-use planning, landscape architecture, urban design and habitat restoration. Certification may complement the use of landscape ecology as a planning framework. Examples discussed in this article include certification as a catalyst for improved forest management; group certification as a basis for landscape planning among small landowners; and certification as a complementary tool for encouraging sound forest management practices on diverse landownerships across a landscape.
The term "keystone species" is applied to certain species the presence of which is deemed essential to the survival of large numbers of other species within a community (Primack, 1993). When viewing a mosaic of forested patches from a landscape perspective, certain holdings may similarly be viewed as anchor pieces, critical to forest ecosystems as a whole because they occupy an important spatial position, contain high biodiversity, serve as critical habitat to a number of species or simply because of their vast size. Such critical forests could be labelled "keystone ownerships".
If systematically applied to keystone ownerships, certification could have a large influence on watersheds and landscapes. By fostering better forestry practices on keystone ownerships, including the establishment of ecological reserves, corridors, well-managed riparian areas and monitoring systems, certification could positively influence neighbouring land holdings by providing a model of good stewardship. SmartWood's certification of the forested lands surrounding Quabbin reservoir, the source of much of eastern Massachusetts' drinking-water, offers an interesting example of a keystone ownership certification (see Box).
Certification of the forests around Quabbin reservoir, Massachusetts, United States
The forest lands surrounding Quabbin reservoir are managed by the Metropolitan District Commission of Massachusetts. The Commission is the largest landowner in the Quabbin watershed, and its primary management objective is water quality, not timber production (NWF/SmartWood, 1997b). The Metropolitan District Commission, because of its size and presence in the Quabbin watershed, is a de facto opinion leader. The catalysing effect of certifyng one well-known ownership could serve to aggregate a number of once disparate land holdings under a common management framework, theoretically making the implementation of landscape ecology principles easier. The Commission reports that one of the principal reasons driving its decision to become certified was: "To provide incentives to other landowners within the Quabbin Reservoir Watershed for improving their forest management practices" (NWF/Smart Wood, 1997b).
ELEMENTS OF LANDSCAPE ECOLOGY THAT CERTIFICATION CANNOT INCORPORATE
This article has illustrated areas where certification organizations have been able, or have the potential, to incorporate aspects of landscape ecology into their certification programmes. However, there are several aspects of landscape ecology that certification is ill-equipped to address. These include protected areas, comprehensive land-use planning, large-scale anthropogenic effects, socio-economic factors and certain cross-boundary issues.
Certification and protected areas
Certified forests cannot serve as adequate substitutes for protected areas. Although certified forests are often required to set aside reserve areas appropriate to the scale of the certified operation, the intensity of the management system and the importance of habitat types found within the ownership, these areas cannot substitute for protected areas. Certified forests can, however, maintain satellite reserves adjacent to core protected areas and may be able to maintain connectivity between protected areas. Protected areas and forest management certification thus play complementary yet distinct roles as forest policy instruments.
Certification and comprehensive land-use planning
In the United States, 58 percent of the forest land is privately owned (Birch, 1996). Therefore, a voluntary, non-governmentally initiated certification cannot be imposed on more than half of the nation's forests. By definition, the purview of independent forest management certification extends exclusively to forest management units. Comprehensive land-use planning may incorporate certification as a voluntary option for landowners but, to be holistic, comprehensive land-use planning must also address matters beyond forest management certification, including the designation of forest reserve areas, agricultural management and urban design and layout.
Certification and large-scale human action
The conversion of human-induced species mix cannot be addressed by certification. Fralish et al. (1991) hypothesize that oak forests and their associated animal and understorey plant communities may become a rare ecosystem within the Midwest United States in the next 100 years. The conversion of oak to beech-maple stands appears to be caused by fire suppression, extirpation of bison herds, the historical disturbance attributed to animal grazing (Fralish et al., 1991) and, perhaps, high-grading, which favours shade-tolerant species such as maple and beech over less tolerant species such as oak. The reintroduction of fire or bison to restore oak stands in the Midwest may be socially unacceptable, especially in areas of high human population density, and in any case costs would be high. Certification schemes cannot be expected to persuade landowners to address landscape-wide conversion of forest type at the level of the individual forest management unit.
Certification and macrosocio-economic factors
Landowner rights and attitudes, tax policies, population pressures, consumption, interest rates, transport networks and a host of other socio-economic factors influence forest policy and management and, ultimately, biodiversity (Turner, Gardner and O'Neill, 1995). Independent certification is not equipped to address the full range of socio-economic variables that may ultimately direct forest use and management. Furthermore, certification clients cannot be expected to bear the full and true costs of maintaining diverse, functioning ecosystems - rather this is a cost that should be borne equally among all of society.
Certification and cross-boundary issues
Certification does not provide landowners with any additional leverage to convince their neighbours to manage collaboratively in the name of landscape ecology. Nor should certification be used as a tool to punish landowners for the irresponsible management practices of their neighbours. The certified Menomonee tribal forest in Wisconsin is an island of forest within a sea of agricultural land. The Menomonee lands serve as a refugium for species that have been driven away from neighbouring forest lands during the conversion of those lands to agriculture. The certification process did not place undue expectations on the tribe for the past actions of neighbouring landowners, as this was a factor beyond the control of the Menomonee forest managers.
Certification is a new forest policy tool, and it is still too early to judge its ultimate impact on forest management. Landscape ecology is also an emerging and evolving discipline with many unanswered questions (Turner, Gardner and O'Neill, 1995). Questioning certification's ability to address landscape ecology provides useful and provocative food for thought and reveals both strengths and weaknesses.
Some independent certification organizations have already attempted to incorporate landscape ecology into their standards for forest management evaluation; their standards include a number of requirements consistent with landscape ecology principles, and the conditions of some of their assessments require compliance with landscape ecology and conservation biology principles. Some certifiers already employ landscape ecologists as members of certification assessment teams and as peer reviewers of certification reports. There is room for certifiers to strive further towards improving the integration of landscape ecology goals with forest certification evaluations. However, it is clear that some issues raised by landscape ecology lie beyond the purview of certification.
Certification should be viewed as one of many tools for achieving forest conservation and landscape ecology goals. Interdisciplinary collaborations among wildlife biologists, landscape ecologists, environmental organizations, land trusts, conservation commissions, community groups and policy-makers could lead to fruitful dialogue and the initiation of pilot projects. Such pilot projects could follow Forman's (1995) concept of an "aggregate with outliers" model, where:
"Land containing humans is best arranged ecologically by aggregating land uses, yet maintaining small patches and corridors of nature throughout developed areas, as well as outliers of human activity spatially arranged along major boundaries."
While coordinating such a multi-disciplinary approach to landscape ecology may be arduous, the theory that certification could be positioned as one of many tools to address and fill critical gaps in buffer-zone management, and thereby complement ecological reserves, is compelling.
Beattie, M., Thompson, C. & Levine, L. 1993. Working with your woodland: a landowner's guide. (Revised edition). Hanover, New Hampshire, USA, University Press of New England.
Birch, T. 1996. Private forest landowners of the United States, 1994. In M. Baughman & N. Goodman, eds. Proceedings of the Symposium on Non-industrial Private Forests. Learning from the past, prospects for the future. 18-20 February, 1996, Washington, DC. St Paul Minnesota, USA, Minnesota Extension Service.
Cabarle, B., Hrubes, R., Elliott, C. & Synnott, T. 1995. Certification accreditation: the need for credible claims. J. Forest., 93(4): 12-16.
Chihambakwe, M., Mupudzi, R. & Mushove, P. 1997. Forestry certification: a developing world viewpoint. Commonwealth Forest. Rev., 76(3): 191-193.
Corbley, K. 1998. It's not easy being green: forest developer pursues green certification with GIS and image processing. Geo Info Systems, 8(2): 32-35.
Coulson, R. & Witter, J. 1984. Forest entomology: ecology and management. New York, John Wiley.
Dramstad, W., Olson, J. & Forman, R. 1996. Landscape ecology principles in landscape architecture and land-use planning. Washington, DC, Island Press.
Dudley, N., Elliott, C. & Stolton, S. 1997. A framework for environmental labeling. Environment, 39(6): 16-20, 42-45.
Ervin, J., Elliott, C., Cabarle, B. & Synnott, T. 1996. Accreditation process. In V. Viana. J. Ervin, R. Donovan, C. Elliott & H. Gholz. eds. Certification of forest products: issues and perspectives, p. 42-53. Washington. DC, Island Press.
Federer, C., Hornbeck, J., Tritton, L., Martin, C., Pierce, R. & Smith, C. 1989. Long-term depletion of calcium and other nutrients in eastern US forests. Environmental Management, 13(5): 593-601.
Forman, R. 1995. Some general principles of landscape and regional ecology. Landscape Ecology, 10(3): 133-142.
Forman, R. & Godron, M. 1986. Landscape ecology. New York, John Wiley.
Fralish, J., Crooks, F., Chambers, J. & Harty, F. 1991. Comparison of presettlement, second-growth and old-growth forest on six site types in the Illinois Shawnee Hills. American Midland Naturalist, 125: 294-309.
Franklin, J. & Forman, R. 1987. Creating landscape patterns by forest cutting: ecological consequences and principles. Landscape Ecology, 1(1): 5-18.
Hansen, E., Fletcher, R. & McAlexander, J. 1998. Sustainable forestry, Swedish style, for Europe's greening market. J. Forest., 96(3): 38-43.
Hedin, L., Granat, L., Likens, G., Buishand, T., Galloway, J., Butler, T. & Rodhe, H. 1994. Steep declines in atmospheric base cations in regions of Europe and North America. Nature, 367: 351-354.
ISF. 1994. Pacific certified ecological forest products: landowner and forester handbook. Redway, California, USA, Institute for Sustainable Forestry.
McIntyre, N. 1995. Effects of forest patch size on avian diversity. Landscape Ecology, 10(2): 85-99.
Noss, R. 1998. A big-picture approach to forest certification: a report for World Wildlife Fund's Forests for Life Campaign in North America. In K. Kessler, D. DellaSala & A. Hackman, eds. Defining a forest vision: World Wildlife Fund's North American Forests for Life Conference. Washington, DC, World Wildlife Fund US.
Noss, R. & Cooperrider, A. 1994. Saving nature's legacy: protecting and restoring biodiversity. Washington, DC, Island Press.
NWF/SmartWood. 1997a. Northeast regional guidelines for the assessment of natural forest management. Montpelier, Vermont, USA, National Wildlife Federation, and Richmond, Vermont, USA, Rainforest Alliance SmartWood Program.
NWF/SmartWood. 1997b. Public certification summary report for natural forest assessment of Metropolitan District Commission's Quabbin Reservoir Lands, Commonwealth of Massachusetts. Montpelier, Vermont, USA, National Wildlife Federation, and Richmond, Vermont, USA, Rainforest Alliance SmartWood Program.
O'Hara, J., Endara, M., Wong, T., Hopkins, C. & Maykish, P., eds. 1994. Timber certification: implications for tropical forest management. Proceedings of a conference hosted by the student chapter of the International Society of Tropical Foresters, 5-6 February 1994. New Haven, Connecticut, USA, Yale School of Forestry.
Primack, R. 1993. Essentials of conservation biology. Sunderland. Massachusetts, USA, Sinauer Associates, Inc.
Risser, P. 1987. Landscape ecology: state-of-the-art. In M. Turner, ed. Landscape heterogeneity and disturbance, p. 3-14. New York, Springer-Verlag.
Risser, P., Karr, J. & Forman, R. 1984. Landscape ecology: directions and approaches. Special Publication No. 2. Champaign, Illinois, USA, Illinois Natural History Survey.
Robinson, S., Thompson, F., Donovan, T., Whitehead, D. & Faaborg, J. 1995. Regional forest fragmentation and the nesting success of migratory birds. Science, 267: 1987-1990.
SAF. 1993. Task force report on sustaining long-term forest health and productivity. Bethesda, Maryland, USA, Society of American Foresters.
SCS. 1992. An evaluation of the forest management practices of the Menominee Tribal Enterprises, (executive summary). Oakland, California, USA, Scientific Certification Systems.
SCS. 1995. The Forest Conservation Program: program description and operations manual. Oakland, California, USA, Scientific Certification Systems.
SCS. 1997. An evaluation of the Pennsylvania Department of Conservation and Natural Resources - Districts 9, 10, 12, 13, 15 and 16 under the SCS Forest Conservation Program, (final report). Oakland, California, USA, Scientific Certification Systems.
Short, H. & Hestbeck, J. 1995. National biotic resource inventories and GAP analysis: problems of scale and unproven assumptions limit a national program. BioScience, 45(8):535-539.
SmartWood. 1997. Public certification summary report for natural forest management of Menominee Tribal Enterprises, Ltd., (executive summary). Richmond, Vermont, USA, SmartWood Program.
Soil Association. 1994. Responsible forestry standards for the United Kingdom. Soil Association's Responsible Forestry Programme. Bristol, UK, Soil Association.
Turner, M. 1989. Landscape ecology: the effect of pattern on process. Annual Review of Ecological Systems, 20: 171-197.
Turner, M., Gardner, R. & O'Neill, R. 1995. Ecological dynamics at broad scales: ecosystems and landscapes. BioScience, Supplement 1995. S-29-S-35.
Urban, D., O'Neill, R. & Shugart, H. 1987. Landscape ecology: a hierarchical perspective can help scientists understand spatial patterns. BioScience, 37(2): 119-127.
Viana, V. 1994. Certification of forest products as a catalyst for change in tropical forest management. In J. O'Hara, M. Endara, T. Wong, C. Hopkins & P. Maykish, eds. Timber certification: implications for tropical forest management, p. 66-79. Proceedings of a conference hosted by the student chapter of the International Society of Tropical Foresters, 5-6 February 1994. New Haven, Connecticut, USA, Yale School of Forestry.
Viana, V., Ervin, J., Donovan, R., Elliott, C. & Gholz, H., eds. 1996. Certification of forest products: issues and perspectives. Washington, DC, Island Press.
Wallin, D., Swanson, F. & Marks, B. 1994. Landscape pattern response to changes in pattern generation rules: land-use legacies in forestry. Ecological Applications, 4(3): 569-580.
Wilcox, B. & Murphy, D. 1985. Conservation strategy: the effects of fragmentation on extinction. American Naturalist, 125: 879-887.
Wilmont, T., Ellsworth, D. & Tyree, M. 1995. Relationships among crown condition, growth, and stand nutrition in seven northern Vermont sugarbushes. Canadian J. Forest Research, 25: 386-397.