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15 Extension Note

Landscape and Connectivity  4  71

Introduction objectives. The Guidebook (B.C. Ministry of and B.C. You accidentally unplug the freezer. Ministry of Environment, Lands and Labour strife removes buses at rush 1995), a component of the Code, hour. A violent storm knocks out the recommends procedures to maintain Biodiversity telephone lines. A highly disturbed biodiversity at both and Management Concepts loses to . stand levels. These procedures, which in What do these events have in com- use principles of ecosystem manage- mon? All are examples of systems in ment tempered by social considera- which an important connection has tions, recognize that an important Ministry contact: been severed. Just like electrical, trans- way to meet the needs of Rick Dawson portation, or communication systems, and range life is to ensure that various B.C. Ministry of Forests Research Program the ecological systems composing habitat types are still connected to 200 - 640 Borland Street require connections to each other. By sustaining landscape Williams Lake, BC V2G 4T1 maintain their functionality. connections, forest- and range- Historically, forest managers dwelling can continue to November 1997 viewed the components that make up spread out and move across and the landscape as separate, unrelated between landscapes. entities. The emerging discipline of This Extension Note is the fourth landscape ecology now focuses on the in a series designed to raise awareness landscape as an interrelated, intercon- of landscape ecology concepts, and to “… an important way nected whole. Landscape ecologists provide background for the ecologi- to meet the habitat place a significant emphasis on the cally-based connections between landscape ele- approach recommended in the needs of forest and ments and their functional roles. Biodiversity Guidebook. The focus here  range life is to ensure The Forest Practices Code is on landscape connectivity. We first acknowledges the importance of land- define and describe connectivity. that are scape ecology concepts by enabling Then we summarize some of the still connected to each district managers to designate plan- ecological principles underlying ning areas called “landscape units,” connectivity, and review its role in other …” each with specific landscape unit maintaining the structural integrity

1 January 2000. Policy direction for biodiversity is now represented by the Landscape Unit Planning Guide. This Extension Note should be regarded as technical background only. 2 Harrison’s chapter in Voller and Harrison’s Conservation for Forested Landscapes (1997, in prep.) is a good reference for those readers wanting an in-depth understanding of connectivity in forested landscapes.

Ministry of Forests Research Program of landscapes, the mechanisms that and functional continuity over both sustain it, and how it relates to biodi- space and time scales. For instance, if versity. We conclude by examining the structural elements (i.e., the how the concepts of connectivity can matrix, patches, and corridors) that be applied at the landscape level. make up a landscape are arranged so that various habitat types are effective- What Is Connectivity? ly linked, species and communities can disperse freely, giving the land- Healthy, diverse ecological systems scape a degree of spatial connectivity. require connections to keep them And if these linkages can be preserved alive and functioning. Landscape ecol- through time, landscape flows and ogists use the concept of connectivity functions will be maintained, giving to describe a landscape’s structural the landscape a degree of temporal connectivity (Figure 1).

Upland to stream-wetland connectivity

Cross-elevational (vertical) connectivity between forested areas

Upland to upland connectivity (horizontal)

Island remnants left after a wildfire (scattered vets; trees along rocky outcrop and stream gullies; trees around wetland)

Wetland to wetland connectivity (horizontal), flat topography

  Some examples of connectivity in forested landscapes (from B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks 1996).

3 Further information about these landscape elements is contained in “Spatial patterns and landscape ecology: Implications for biodiversity,” the third in this series of landscape ecology Extension Notes.

 Landscape structure therefore natural connections between forested strongly influences the flow of energy, ecosystems may also be severed by nutrients, water, disturbances, as well timber harvesting, as well as by urban- as organisms and their genes (Noss ization, agriculture, and other 1991). For example, the particular development activities. arrangement of open and forested areas in a watershed could affect the Ecological Principles direction of cold air drainage and wind, the incidence and extent of MacArthur and Wilson’s (1967) influ- flooding, the movement of wildfires ential theory of island and occurrence of windthrow, the provided the basis for early notions spread of seed, insects, and mycor- about landscape connectivity. They rhizal fungi, and the daily and observed that the number of species seasonal migration of wildlife. (or the species “richness”) present in is the Pacific and other island archipelagoes opposite of connectivity. Forested was related to the individual island’s landscapes are disrupted when large area and degree of isolation. Patterns contiguous forest patches are trans- of species richness resulted from the formed into smaller patches equilibrium that tends to develop surrounded by disturbed areas. This between the rate of species coloniza- disruption can occur through natural tion and extinction. For instance, disturbances such as fire, landslides, near-shore islands would be settled by windthrow, and insect attack. The species that could fly, swim, or drift from the adjacent mainland. There- fore, because of their proximity, these islands were effectively “connected” to the mainland. Conversely, distant oceanic islands had lower species rich- ness because their connectivity to the mainland was much lower. This theo- ry was later adapted to include “habitat islands” created by habitat fragmentation (Wilson and Willis 1975): as specific (e.g., old- growth valley-bottom spruce) become isolated from one another, natural species diversity decreases. The theory of island biogeography was further extended when the idea of metapopulations was introduced (Levins 1970) (Figure 2). This model describes how interconnected popula- tions of species exist and interrelate, and recognizes that some animal and   Landscape connectivity allows several individual populations of a plant populations require linkages species to exist in, and move freely between, a network of suitable between habitats. When landscape habitat patches. This connected collection of populations consti- connectivity is breached, certain con- tutes a “metapopulation.” Species have become extirpated in the tinuous, stable populations are empty habitat patch (upper left), and the loss of connectivity to converted into populations that the metapopulation prevents recolonization (from Harrison 1996). become more and more disrupted and

 unstable. Some local populations can Natural features such as riparian suffer complete elimination (or “extir- habitats along a stream or river often pation”), but total extinction of the provide good corridors at the land- species may be prevented by the suc- scape level because they encompass a cessful recolonizing efforts of diversity of habitats and topographic connected populations. The basic gradients. Branching drainage pat- assumption is that if appropriate habi- terns provide important landscape tat types are connected, organisms will connections by linking upper and disperse among them (Merriam 1991). midslopes with valley bottoms. Human-built features such as Maintaining Corridors fencerows can also be used to create Preserving habitat and dispersal connections between landscape patch- routes to maintain landscape-scale es. As well, individual patches connectivity is a popular research themselves may provide connections topic in landscape ecology. if they are suitable for a species to Researchers (see, for example, Voller move through or live in. and Harrison’s [1997, in prep.] litera- Few data currently exist on the use ture review) suggest that habitat of corridors, and their perceived isolation and the attendant loss of nat- advantages have been questioned. ural species diversity can be reduced However, most scientists acknowledge by designating connective “corridors.” that natural connectivity is important These important elements of land- and should be retained before land- scape structure are usually continuous scapes are disturbed. A number of remnants of naturally occurring vege- pros and cons concerning the use of tation which allow species or their corridors are presented in Table 1. genes to move between patches of undisturbed habitat (Saunders and Connectivity and Biodiversity Hobbs 1991). The loss of landscape connectivity, The presence of corridors in the often discussed as habitat fragmenta- landscape can: tion, is considered by some landscape • ease the movement of flora ecologists to be among the greatest and fauna; threats to natural biological diversity. • act as a semi-permeable barrier, Forest fragmentation leads to declines thus limiting the effects of negative in biodiversity in three ways: incidents across the corridor (e.g., 1. through habitat loss (e.g., by con- vegetated corridors absorb the verting forests from natural to effects of water and nutrient runoff managed stands or to other uses and moderate the force of winds); such as pastures); • provide habitat for some 2. through increases in “edge effects,” species; and the modified environmental condi- • act as a source of environmental tions found at the boundaries and biotic effects on the surround- between habitats (e.g., by reducing ing matrix (e.g., colonizing the size of forest patches); and organisms may move from the cor- 3. through increases in habitat isola- ridor to the surrounding matrix, or tion (e.g., by imposing barriers to the corridor may moderate the gene flow and dispersal). local microclimate through shad- ing) (Forman 1983).

   Potential advantages and disadvantages of corridors (adapted from Noss 1987)

Advantages Disadvantages Corridors could: Corridors could: 1. Increase inflow of species to a 1. Increase inflow of species to a reserve, which in turn could: reserve, which in turn could: • increase or maintain species rich- • lead to the spread of epidemic dis- ness and diversity; eases, insect pests, exotic species, • provide a “” or permit weeds, and other undesirable extinct local populations to re- species into reserves and across the establish; and landscape; and • maintain genetic variation within • decrease the genetic variation isolated populations. among populations through the 2. Provide increased foraging area for loss of local variants. wide-ranging species. 2. Enable the spread of fire and other 3. Provide predator-escape cover for disturbances (“contagious catas- species moving between patches. trophes”). 4. Provide a mix of accessible habitats 3. Increase the exposure of wildlife to and successional stages for species hunters, poachers, and other that require a variety of habitats for predators. different activities or stages in their 4. Impede, in the case of riparian strips life cycles. used as corridors, the dispersal or 5. Provide alternative shelter from large survival of upland species. disturbances (a “fire escape”). 5. Conflict with strategies to preserve 6. Provide “greenbelts” to limit urban endangered species habitat (when the sprawl, abate pollution, provide inherent quality of a corridor habitat recreational opportunities, and is low). enhance scenery and land values.

Small populations of poor dis- significant connectivity, managed to persers, restricted to isolated patches maintain all its original mammalian of forest and separated by roads, clear- fauna. ings, and other barriers, may not be Many studies on the importance of capable of surviving in the long term. landscape connectivity have involved The loss or gain of only a few species small mammals and birds. Small can often be enough to tip the balance mammals play several roles in forested and destabilize the whole community. ecosystems and are a critical compo- Multiple reserves linked by corri- nent of biodiversity. Various rodents, dors offer a regional solution to for example, distribute mycorrhizal preserving many unique species. For fungi, that are essential to conifer instance, a study of in 14 seedling survival. They also constitute western North American parks the majority of the diet for many showed that 13 parks had lost 43% of species (e.g., marten, coyotes, and their historic mammal species in three owls and other raptors) and therefore taxonomic orders: lagomorphs, carni- are an integral part of normal ecosys- vores, and ungulates (Newmark 1987). tem functioning. Rodents frequently Only the Kootenay-Banff-Jasper-Yoho use corridors between both forested system, which is characterized by and open patches in the landscape.

 These corridors are important for matrix. As human development pro- maintaining connections among their ceeds, this matrix is reduced and isolated populations. Some research- many habitats previously linked can ers suggest that rodents living in become isolated. isolated populations have lower The Biodiversity Guidebook outlines growth rates and are more prone to two ways to mitigate this loss of nat- extinction than are connected popula- ural connectivity in the forest matrix: tions (Craig et al. 1997). 1. by maintaining networks of corri- Corridors are also important for dors that can sustain some of the birds living in a fragmented habitat. linkages present in the natural One study, which investigated the landscape; and Forest Ecosystem Networks concept of habitat islands, showed 2. by managing the area between that larger areas of habitat generally these corridors (i.e., the mature McDougall (1991) proposed supported more bird species than did and old forest matrix) to maintain the use of Forest Ecosystem smaller areas (MacClintock et al. the natural forest characteristics Network (FEN) as a way to 1977). However, there was one impor- that certain species require for manage biodiversity across landscapes. This is now the tant exception. One 14-ha site was habitat and movement purposes. recommended long-term found to support a greater number of management approach to bird species than many of the larger Since most of the landscape repre- meet old-growth and con- preserves. Unlike the larger sites sam- sents the area between corridors, nectivity objectives for pled, this habitat island was connected careful management to preserve landscape units in British Columbia. by corridors to a 162-ha site and a fur- the area’s connectivity and habitat A FEN is a planned land- ther 4045-ha forest. The species attributes over time is critical. The scape zone composed of common in the 162-ha preserve were Biodiversity Guidebook recommends reserves, corridors, and also common in the smaller fragment. that forest managers apply both buffers. It serves to maintain or restore the natural con- The authors concluded that forest strategies when planning activities in a nectivity within a landscape species could live and breed success- landscape unit. In general, the type unit and is important for: fully on small habitat islands provided and degree of connectivity that exists • maintaining natural forest these fragments were in turn connect- in the natural landscape is the guide ecosystem processes; ed to larger tracts of forest matrix. that should be used to develop land- • providing interior habitat; and scape plans for connectivity. • allowing for dispersal, recol- Applying Concepts of Connect- onization, and movement. ivity to Protect Biodiversity Maintaining Corridor Connectivity Most connectivity objectives should FENs consist of a variety of To landscape-level forest planners, be met using a coarse-filter ecosystem fully protected areas, sensi- tive areas, and old-growth the term “connectivity” means the management approach. This approach management areas. degree to which various ecological provides a generic solution for the components are linked to one anoth- ecosystem connectivity needs of most er over time to form an interconnect- species in the landscape unit. ed network of forest matrix and However, in some landscape units the corridors. The extent of this intercon- dispersal requirements of certain nectedness and the characteristics of regionally important species (e.g., the linkages vary depending on an mountain goat populations that move area’s topography and natural distur- seasonally between two alpine areas) bance regime. As important as corri- may require a unique planning solu- dors are, however, most of the tion. In this case, a fine-filter connectivity in mature and old forests approach would accommodate the in natural landscapes is through the

4 The emphasis in British Columbia is placed on maintaining the connectivity of late successional forests because forest management in many areas of the province reduces both the proportion and continuity of these forests.

 needs of these species by designating tions for movement, while wide- specific movement corridors. ranging, large mammals such as Depending on a unit’s connectivity grizzly bears might require landscape- objectives, corridors should be man- scale corridors. Of course, all linkages, aged as either permanent or shifting regardless of their width, must con- features in the landscape. Permanent nect areas of useful habitat managed corridors (i.e., those with a fixed loca- for the appropriate attribute. tion through time) are simple and Continuity of Linkages Corridors flexible management tools that, should be designed to maintain conti- because of their carefully chosen loca- nuity through time. Therefore, tion, can be more biologically effective consider the effects of both natural than shifting corridors. An appropri- disturbances (such as insect mortality) ate combination of approaches and planned disturbances (such as (e.g., keeping some patches as harvesting or road building). reserves, creating small clearcuts in If permanent corridors are to be some areas and using selection har- used, then the number of road cross- vesting in others, and practising ings should be minimized and the intensive management to protect old- corridors restored as necessary after growth attributes overall) is the best natural disturbances. If shifting way to preserve the integrity of these corridors are to be used, then it is corridors. Shifting corridors, on the important to ensure that replacement other hand, need be maintained only corridors have the required attributes until the adjacent replacement link- before existing corridors are harvested. ages have developed the necessary In all landscape plans, connectivity attributes. objectives must acknowledge that Other considerations in the design linkages are a long-term requirement. and management of corridor connec- Habitat Quality The habitat quality tivity include: within networks is another important • corridor width and composition; element of connectivity. In managed • continuity of linkages; and forests, corridors across harvested • habitat quality. lands must provide areas of interior forest habitat characteristics to facili- Corridor Width Corridor width and tate the movement of organisms. composition are important factors in Landscape planning might be simpli- determining how effective a network fied by locating corridors in inoper- of interconnected corridors will be, able or non-productive timber areas. but few guidelines exist to indicate However, connectivity must also be how these design considerations actu- maintained in productive timber areas ally influence animal movements. if species prefer such habitats. Generally, however, wide and contin- uous corridors are most likely to Managing the Forest Matrix foster movements. Since corridors in managed land- If designed for specific species, an scapes will usually only cover a small effective dispersal corridor should be proportion of the area, management of a size that responds to the needs of of habitat in the surrounding matrix those species. Therefore, the life histo- is also extremely important for main- ries and requirements of the fauna taining connectivity. In many land- that will use a corridor should be scapes and for numerous organisms, assessed. For instance, some birds the matrix will be as important, or might use narrow vegetated connec- more important, than corridors for

 connectivity. For example, organisms References adapted to landscapes in the Sub- Boreal Pine-Spruce Zone will require British Columbia Ministry of Forests a matrix of large patch sizes and fre- and B.C. Ministry of Environment, quent reserve “islands” to mimic the Lands and Parks. 1995. Biodiversity attributes of their natural landscape. guidebook. B.C. Forest Practices These landscapes did not have large Code. Victoria, B.C. continuous areas of old forest, but did British Columbia Ministry of Forests have frequent small patches of old for- and B.C. Ministry of Environment, est and linear riparian strips of old Lands and Parks. 1996. Landscape forest resulting from natural fire skips. level biodiversity course workbook. Planned corridors in these landscapes Victoria, B.C. may therefore be largely in riparian Craig, V., W. Klenner, and T. Sullivan. areas. 1997. Relationships between small For other landscape types contain- mammals and downed wood at ing species adapted to the natural Sicamous Creek. In Sicamous pattern of large continuous areas of Creek Silvicultural Systems mature and old forests, simply main- Workshop Proceedings. C. taining a few remnant corridors will Hollstedt and A. Vyse (editors). likely not meet all the connectivity B.C. Ministry of Forests, Victoria, requirements. Managing these land- B.C. Working Paper 24, pp. 243–53. scapes will require, in addition to the Forman, R.T.T. 1983. Corridors in a development of wide corridors, the landscape: their ecological struc- maintenance of matrix connectivity ture and function. Ekologia by: 2(4):375–87. • limiting the area of young and Harrison, S. 1996. Connectivity. B.C. pole-sized forest through time; Ministry of Forests, Prince George • maintaining structural attributes Forest Region, Prince George, B.C. such as snags, residual trees, and Forest Research Note #PG-03. coarse woody debris; and Levins, R. 1970. Extinction. In Some • practising uneven-aged mathematical questions in biology: in some portions of the matrix. lectures on mathematics on the life sciences. M. Gerstenhaber (editor). Maintaining landscape connectivity American Mathematical Society, is an essential aspect of forest land- Providence, R.I. Vol. 2:7–107. scape management for biodiversity. MacArthur, R.H. and E.O. Wilson. We need to consider and implement 1967. The theory of island biogeog- connectivity recommendations raphy. Princeton University Press, carefully in each landscape plan. Princeton, N.J. Experience, research, and monitoring MacClintock, L., R.F. Whitcomb, and of our efforts will allow us to improve B.L. Whitcomb. 1977. Island bio- our understanding and refine how we and “habitat islands” of manage our forests to maintain this eastern forests. American Birds vital attribute of healthy landscapes. 31(1):3–16.

Text by Susan Bannerman

 McDougall, I.A. 1991. Forest ecosys- Saunders, D.A. and R.J. Hobbs. 1991. tem networks: a strategy for The role of corridors in conserva- managing biological diversity. B.C. tion: what do we know and where Ministry of Environment, Lands do we go? In conservancy 2: and Parks, Victoria, B.C. The role of corridors. D.A. Unpublished report. Saunders and R.J. Hobbs (editors). Merriam, G. 1991. Corridors and con- Surrey Beatty and Sons, New South nectivity: animal populations in , Aust., pp. 421–7. heterogeneous environments. In Voller, J. and S. Harrison (editors). Nature conservancy 2: The role of [1997]. for corridors. D.A. Saunders and R.J. forested landscapes. B.C. Ministry Hobbs (editors). Surrey Beatty and of Forests, Research Branch, Sons, New South Wales, Aust., Victoria, B.C. In preparation. pp. 133–42. Wilson, E.O. and E.O. Willis. 1975. Newmark, W.D. 1987. A land-bridge Applied biogeography. In Ecology island perspective on mammalian and evolution of communities. M. extinctions in western North Cody and J.M. Diamond (editors). American parks. Nature 325:430–2. Harvard University Press, Noss, R.F. 1987. Corridors in real Cambridge, Mass. landscapes: a reply to Simberloff and Cox. Conservation Biology 1(2):159–64. ______. 1991. Landscape connectivity: different functions at different scales. In Landscape linkages and biodiversity. W.E. Hudson (editor). Defenders of Wildlife, Washington, D.C.

The use of trade, firm or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the Government of British Columbia of any product or service to the exclusion of others that may also be suitable. This Extension Note should be regarded as technical background only.