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Towards a Definition of Biological Corridor

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Towards a Definition of Biological Corridor INTEGRATING PEOPLE AND WILDLIFE FOR A SUSTAINABLE FUTURE JOHN A. BISSONETTE and PAUL R. KRAUSMAN The Wildlife Society Bethesda, Maryland 1995 436 International Wildlife Management Congress 10.6 10.6 In common usage, corridor has been defined as 1) “A gallery or passageway. one into which compartments or rooms open,” 2) "A gallery or TOWARDS A DEFINITION OF passageway connecting several apartments of a BIOLOGICAL CORRIDOR building,” 3) “. a narrow passageway or route” (Merriam Webster and Co. 1961) and as numerous DANIEL K. ROSENBERG similar definitions. The common elements of these Oregon Cooperative Wildlife Research Unit. Department definitions most relevant to their ecological appli- of Fisheries and Wildlife, Oregon State University, cation are the terms passageway and connecting. Corvallis. OR 97331, USA With “passageway” there is an implicit concept that the corridor is narrow relative to the habitats BARRY R. NOON being interconnected. In the ecological literature. U.S.D.A. Forest Service, Redwood Sciences Laboratory, corridors have been defined as 1 of 3 major land- 1700 Bayview Drive, Arcata, CA 9552 1, USA scape elements: patch. matrix. and corridor (For- man and Godron 1986:23). In a thorough discus- E. CHARLES MESLOW sion of the principles of landscape ecology. U.S. Fish and Wildlife Service. Oregon Cooperative corridors were defined as “. narrow strips of land Wildlife Research Unit, Department of Fisheries and which differ from the matrix on either side. Corri- Wildlife. Oregon State University. Corvallis. OR dors may be isolated strips. but are usually attached 97331, USA to a patch of somewhat similar vegetations” (For- man and Godron 1986:123). This definition char- Abstract: Lack of clear, unambiguous criteria that acterizes corridors in terms of their shape and spa- distinguishes a linear habitat patch as a corridor tial context. but does not explicitly ascribe a contributes to controversy over the value of corri- functional role. Earlier in their discussion. Forman dors for wildlife conservation. The definitions of and Godron (1986:121) emphasized the possible biological corridors have been vague or inconsis- transport function i.e.. movement of objects) of tent, and often they confound form and function. corridors. arising as a consequence of their shape Explicit criteria that can differentiate between a lin- and context. rather than as a necessary condition to ear habitat patch and a biological corridor have not ascribe the term “corridor“ to a linear element. been formulated. We reviewed the use of the term Given the above definitions. the necessary cri- “corridor-’ in the ecological literature. and attempt- teria for determining if a linear landscape element ed to clarify the concept of biological corridor. is a corridor are ambiguous. One definition empha- sizes function (passageway from one location to an- Resumen: La falta de claridez y criterios ambiguos other) while others stress form and context (narrow, para distinguir un parche de habitat linear de un and contrasting with the environment on its edges,. corredor contribuye a la controversia de1 valor de Thus. when issues such as the significance of cor- los corredores en la conversacion de de fauna sil- ridors to the maintenance of biological diversity are vestre. Las definiciones de corredores biol@cos debated (Noss 1987. Simberloff and Cox 1987. han sido vagas e inconsistentes y frecuentemente Saunders and Hobbs 1991a). disagreement may confunden la forma y funcion. Un criterio explicito arise simply as a consequence of divergent under- que pueda diferenciar entre un parche de habitat standings of the corridor concept. linear y un corredor biol6gico no han sido aun for- Our work on corridors has been supported by the mulados. Nosotros revisamos el uso de1 termino U. S. Forest Service. Redwood Sciences Labora- "corredor" en la literatura ecoltigica en un intento tory. Arcata, California. and by the Oregon Coop- de clarificar el concepto de corredor biol&ico. erative Wildlife Research Unit. which is operated with the cooperation of Oregon State University. Key words: biological corridor. connectivity, cor- Oregon Department of Fish and Wildlife. U.S. Fish ridor, habitat corridor. habitat patch. landscape. lin- and Wildlife Service, and the Wildlife Management ear patch. Institute. We thank S. DeStefano and L. D. Harris for helpful comments on improving this manu- script. The inclusion of linear landscape elements into wildlife conservation plans has gained wide accep- USE OF THE TERM “CORRIDOR” IN tance as an important aspect of conservation strat- PUBLISHED STUDIES egy (Noss 1987, Saunders and Hobbs 199la, Mann Corridors have been described as linear patches of and Plummer 1993). Arguments for the importance natural vegetation that provide habitat for wildlife, of corridors as landscape elements can be found in either as temporary use areas (part of a home range) natural resource ecology and human ecology (For- or as a place of permanent residence (an inclusive man and Godron 1986:121). The use of the term home range). For example. Maelfait and De Keer corridor in a broad spectrum of disciplines has con- (1990) in their study of field edges in Belgium, con- tributed to vague and sometimes contradictory def- cluded that corridors were effective in the conser- initions, and has incited vigorous debate over their vation of invertebrates. Their conclusion was based importance to conservation. on the observation that the “corridor” provided . 10.6 Towa Definition of Corridor. Ro.renbe r!: et al. 437 habitat (both temporary and permanent) for many a corridor is a type of landscape element that es- species that were not adapted to the surrounding tablishes connectivity via ‘a continuous narrow pasture. They recognized the possible importance patch of vegetation that facilitates movement of the corridor for migration, yet their conclusion among larger habitat patches and prevents their iso- of corridor value was based exclusively on the role lation (Merriam 1984). Soule’ and Gilpin (l991:3) of providing, habitat. In a similar example, Van provide a clear and concise definition: “. a linear Dorp and Opdam (1987) assert the functional role two-dimensional landscape element that connects of corridors as connecting-networks, yet describe two or more patches of wildlife (animal) habitat corridors in terms of their habitat composition, not that have been connected in historical time; it is in terms of any effects on animal movement. meant as a conduit for animals." Bennet (1990: Linear landscape elements arising from human 109) defined habitat corridors as “. narrow con- design, such as power-lines and roadside vegetation necting strips of favored habitat.” Szacki (1987) are sometimes referred to as corridors with an im- limits the discussion of corridor effectiveness to the plicit assumption of ecological value. For example. frequency of movement. without considering its Kroodsma (1987) described bird densities and dis- vaIue as habitat. Dmowski and Kozakiewicz (1990) tribution in brushy power-line habitat and along the defined corridors similarly, and explicitly equated edge of a forest in Tennessee (U.S.). Although data corridors with connectivity, and discussed the role were not presented that demonstrated enhanced of a narrow belt of shrubs in enhancing movement movement of birds. the habitat was referred to as of birds between 2 (different) habitats and in di- “brush>, corridor vegetation’ (Kroodsma 1987: recting movement. Merriam and Lanoue (1990: 282) consistent with the habitat definition of For- 124) restricted their use of the term corridor by man and Godron (1986). Similarly. roadside vege- calling it “movement corridor.” thus implicitly sug- tation is often considered as a corridor. For exam- gesting other functions for other types of corridors. ple. several papers included in Saunders and Hobbs A functional definition was adopted by Reh and (1991a) on corridors discussed the advantages of Seitz (1990) in their discussion of corridors as con- managing roadside vegetation as habitat. nectors among otherwise isolated populations of There are numerous examples of “corridor” frogs. In this case. corridors were discussed as fa- used to signify its structural attributes as linear hab- cilitating and directing movement. itat and its functional role as a dispersal conduit. In This brief Iiterature review should reveal that reply to a paper questioning the merits of corridors corridors mean different things to different authors. (Simberloff and Cox 1987). Noss (1987) listed first and this ambiguity has contributed to the current those criteria associated with the enhanced move- controversy over their efficacy as conservation ment function. Secondarily. factors associated with tools. Without a clear definition of corridors. de- habitat attributes were described and the discussion fined in terms of their functional effects on animal of these factors imply the habitat criteria (i.e. form) behavior, it is impossible to determine their value for corridors: “Scenery, recreation, pollution abare- as management tools. ment. and land value enhancement are what usually motivate planners to draw corridors into their de- A MODEL TO CLARIFY THE MEANING signs" (Noss 1987:162). Although a focus on form OF BIOLOGICAL CORRIDORS does not preclude a functional detinition of corri- To distinguish between a linear landscape element dor. it suggests that either set of criteria. facilitated as habitat or as a biological corridor, we need to movement or spatial structure,
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