THE ROLE of ABORISTS in PROVIDING WILDLIFE HABITAT and LANDSCAPE LINKAGES THROUGHOUT the URBAN FOREST by Julian A

160 Dunster: Providing Wildlife Habitat in the Urban Forest

THE ROLE OF ABORISTS IN PROVIDING WILDLIFE HABITAT AND LANDSCAPE LINKAGES THROUGHOUT THE URBAN FOREST by Julian A. Dunster

Abstract. In recent years, great advances have been made "Not many." Conversely, how many arborists un- in arboriculture, but the main design professions, the derstand the mindset of these other professions? general public, and some arborists still lack understanding about the ecological functions of trees for other organisms, Again, the likely answer is "Not many." and how these ecological functions and processes connect The profession of arboriculture has advanced across larger landscapes. Consequently, many opportuni- considerably in recent years. We now have a ties for the retention or creation of wildlife habitat in the better sense of how good pruning should be un- urban forest are still being lost. Some of these opportunities are discussed, along with examples from British Columbia. dertaken; we know more about roots, stress re- A selection of references from related fields is included to sponses, good and bad retention, planting, and provide a basis for further reading and understanding about plant care practices. But all of this has focused landscape ecology, greenways, wildlife trees, and how on what the arboriculture profession considers arborists might integrate the principles from these fields into their practice. to be the best means of maintaining a healthy Keywords. Urban forest; wildlife habitat; landscape tree. Less attention has been given to the role ecology; linkages; wildlife trees. of these trees within an urban or rural ecosystem, and not all arborists may be aware of the contribution that trees make to the larger landscape in terms of ecosystem function and eco- Arborists play an important role in managing ur- system processes. Consequently, we miss an ban forests. Our prescriptions, management, and important opportunity to advise the design pro- maintenance activities determine the structure and fessions about what other ecological functions function of individual trees to stands of trees and a tree might provide. entire forests in the larger landscape on public In the field of landscape ecology, the notion of and private lands. Yet the contemporary focus is connectivity between larger patches or nodes of on the single tree, or on a group of trees in re- habitat is central to the function of a healthy sys- sponse to a single client. The situation is not helped tem (Forman and Gordon 1986; Hodge 1995). by the pronounced division of responsibilities seen Stream corridors and their associated riparian in most local government structures: the parks de- habitats, parks with forest components, and single partment looks after street trees and greenspaces, trees or groups of trees on private and public the planning department looks after new develop- lands all contribute to a mosaic of landscape con- ments and redevelopments, and all too often, the nectivity. For many species of wildlife, connec- engineering department works in isolation from tions between larger nodes of habitat may be everyone else. essential to survival because fragmentation, and Complicating this fragmented governance is an subsequent isolation of populations and their as- all-too-common lack of awareness, especially at sociated habitats, may lead to long-term loss of the senior decision-making and political levels, genetic flux, insufficient habitat area, and poten- about contemporary science and the need for in- tial extirpation from the area, perhaps even ex- terdisciplinary design approaches. How many tinction. A large body of literature is devoted to members of the design professions such as engi- the theme of landscape linkages, which in the neering, architecture, planning, biology, and land- urban and rural context have been termed scape architecture actually know what trees and "greenways" (Hudson 1991; Labaree 1992; wildlife require? Arborists would probably respond, Smith and Hellmund 1993; Ministry of ELP 1995). Journal of Arboriculture 24(3): May 1998 161

Along similar lines, it is common to see land- Trees as a Source of Wildlife Habitat scapes formerly denuded of vegetation being re- Trees are a large and highly visible component stored as forests. This aspect is particularly of greenways. With the increasing focus on these evident in parts of Europe where lands formerly landscape linkages, typically situated on a mix under agriculture or industrial uses are now aban- of public and private lands, arborists can antici- doned. The literature on forest restoration, or re- pate a larger role in managing these systems. creation of forests, is plentiful and contains However, management of trees within greenway excellent guidance for arborists wishing to better systems requires a focus beyond simple prun- understand the larger role of trees in a functional ing and health care. In many cases, a dead or ecosystem (Forestry Commission 1990, 1991; dying tree is just as important to the overall Hodge 1995; Rodwell and Patterson 1995). The health of the ecosystem as the live and theme of ecosystem functions within urban for- healthy trees. ests is also well documented (Bradley 1995; Kollin The traditional response to dead or dying 1994, 1995) and provides further insight about trees has been to remove them either because how trees provide so much more than shade, aes- they are hazards, or to "tidy up" the landscape thetics, climate control, etc. The management of to avoid an anthropocentric perception of un- urban forests, especially small remnant patches, kempt appearances. But this tidying-up ap- and the manner in which these can be used to proach can be ecologically damaging, and create important patches of wildlife habitat (Agee arborists need to better understand the role of 1995; Milligan Raedeke and Raedeke 1995) are dead or dying trees as a source of habitat. For integral to understanding the larger role that ar- example, large pieces of a tree, known in forest borists could assume. Similarly, at the industrial management as coarse woody debris, provide scale of forest management, much new evidence a source of food for many insects and fungi. In- is emerging about the manner in which wildlife sects are a food source for the birds, which them- habitat can be better integrated with commercial selves help maintain insect populations at harvesting (Bradford et al. 1996). endemic levels. Small mammals find refuge and Because of the rapid urban growth in many breeding areas in decayed logs, and it has been parts of British Columbia, the British Columbia Min- shown that dispersal of beneficial forest mycor- istry of Environment issued an informative series rhizae is a direct function of small mammal popu- of publications dealing with development and the lations and the dispersal of spores in their fecal environment. We now have detailed guidelines for pellets (Maser 1988; Machmer and Steeger developments next to streams and rivers and ar- 1993). eas of specialized habitat (Chillibeck 1993; Minis- In industrial forest management, particularly in try of ELP 1994), as well as guidelines for the United States and more recently in Canada, integrating development with greenways (Minis- there has been a strong drive to manage the for- try of ELP 1995). Coupled with the emerging shift ests for more than just timber. Wildlife trees, de- towards the creation of greenways and landscape fined as "tree[s] that provide ... present or future linkages across entire municipalities or regional critical habitat for the maintenance or enhance- landscapes is the increasing need for a better un- ment of wildlife" (Dunster and Dunster 1996) have derstanding of trees. What makes them suitable value for many different species and are used for for retention(Dunster 1995, 1996)? Which prac- many different purposes including nesting, perch- tices maximize the chances for long-term survival? ing, feeding, or roosting. The species that use wild- What is the best approach for design and life trees can be sorted into 5 categories postconstruction management? When a broader (Maser 1988; Backhouse 1992; Wildlife Tree view is taken, it is clear that arborists can assist Comm. 1992): other professionals in deciding how best to de- 1. Primary cavity excavators: Examples in- sign and manage for sustainable urban forests and clude woodpeckers, flickers and sapsuck- the creation of wildlife habitat. ers, chickadees, and nuthatches, all of 162 Dunster: Providing Wildlife Habitat in the Urban Forest

which use their hard beaks to dig out holes in soft, decaying wood. These species make new cavities each year, leaving the old ones for other species to use. 2. Secondary cavity users: These species cannot excavate cavities by themselves, but use abandoned holes to nest and raise young, to store food, or simply as shelter. Examples are owls, tree swallows, blue- birds, and wood ducks, in addition to mammals such as martens, raccoons, flying squirrels, and deer mice. 3. Open nesters. These are the larger birds that require a place for heavy nests—typically birds of prey such as eagles, ospreys, or great blue herons. They can use dead or live trees but usually prefer trees with a broken top or flat crown that can support the nest and yet retain a clear field of view in all (or most) directions. Figure 1. Cavities occur in many forms and have 4. Other mammals: This category includes many uses for different species (from Thomas mammals such as bears (which often build 1979). dens in the hollow base of larger trees) and other large mammals such as caribou, In British Columbia, over 90 species are known which use the lichens growing on branches. to depend to some extent on wildlife trees, and Smaller mammals, such as bats and mice, about 18% of all bird species breed in the cavi- find opportunities for shelter and nesting ties of wildlife trees, including several rare and under loose bark and in other small endangered species (Wildlife Tree Comm. 1992; cavities. Machmer and Steeger 1993). The establishment 5. Amphibians: Amphibians use dead and of the British Columbia Wildlife Tree Committee, dying trees as a shelter and brooding habi- jointly administered by the Ministry of Forests, tat, especially once the wood is in an ad- the Ministry of Environment, Lands, and Parks, vanced stage of decay and is soft and and the Workers Compensation Board, has given spongy enough to tunnel into, yet moist some credibility to the creation and retention of enough to protect the occupants. wildlife trees in industrial operations. This com- In addition, decaying trees are often a source mittee has established a training function to per- of nutrition at various levels of the food chain. For mit the identification and retention of trees example, insects that attack dying trees often in- considered necessary for wildlife (Wildlife Tree troduce fungal agents that help accelerate the Comm. 1992), and the retention of such trees has decay processes. These insects become food for now been extended into urban situations and foraging birds, and fungi make the wood suitable greenways. for the cavity excavators. The use of wildlife trees One of the simplest means of defining a land- in industrial forestry is well established (Thomas scape corridor (connection) on the ground is to 1970; Bull et al. 1986; Morrison et al. 1986; retain the vegetation alongside creeks, streams, Bradford et al. 1996; Parks et al. 1997). Trees with and rivers. In the British Columbia development useful cavities for wildlife can be live, or can be guidelines, a 15 m (50 ft) setback from the top of partly or wholly dead, as shown in Figure 1. the bank is now considered a minimum amount Journal of Arboriculture 24(3): May 1998 163

of land to be left undeveloped. This setback zone sity gain in one location in order to offset devel- protects the water body and retains a narrow area opment losses due to environmental protection. of riparian habitat, including trees. However, such In other cases, it may be necessary to carefully a narrow band of remnant forest is quite often remove the unstable forest overstory (such as unsuitable for safe tree retention if it contains tall edge trees with no windfirmness, or suppressed trees next to new residential developments trees with little or no rooting system) using spe- (Dunster 1995). From a fisheries and environment cialized logging techniques involving a suspended viewpoint, trees provide shade for the water; lift of the felled trees to minimize ground distur- cooler water holds higher oxygen concentrations, bances. The relatively undisturbed ground is then which in turn helps ensure fish survival. At the replanted. In some instances, the material being same time, litter from the trees provides nutrient removed is placed in a stable position on the inputs for the various insect fauna, and hence, a ground and left to decay in place, thus ensuring source of food for fish, and the tree roots stabi- no net loss of biomass from the site. Such tech- lize the bank slopes. As a unit, the entire riparian niques have been used successfully by the au- zone provides a narrow band of habitat along thor; the coarse woody debris is important habitat which certain species of animal can travel, rea- and declines in place over time, while replanted sonably free of outside disturbance, although in trees develop very rapidly to create a new forest a 30-m (1OO-ft) band of forest, this is sometimes area that is better adapted to the new site condi- hard to achieve. tions (Dunster 1995). A common problem is that the retained trees, The creation of a good wildlife tree requires so greatly desired for environmental purposes, understanding its purpose. As a tree declines and are often too tall, too isolated, and too hazard- dies, it provides habitat for a range of species. ous to justify their retention. This often produces According to a a well-defined classification an immediate source of friction between those scheme for wildlife trees (snags) and logs on the wanting the trees for their environmental benefits ground, each stage of decomposition has its own and those wanting them removed or treated to particular uses for various species. The scheme reduce the hazards. To reduce the levels of fric- shown in Figure 2 is typical. tion, alternative approaches have been devel- A Class 1 wildlife tree is live and healthy. It may oped. The width of the setback zone design can posses some small cavities that are a result of de- be designed according to the development den- cay, not primary excavation. The crown foliage and sity, terrain, and vegetation types. Areas with branches are used for nesting, perching, or as ter- young forest cover that can adapt to changed mi- ritorial markers. If large lateral limbs are present, croclimatic and hydrological conditions resulting large birds of prey may nest or perch on them. from adjacent developments may be more suit- A Class 2 tree is at the initial stages of evident able for retention than areas covered with ma- decline but still living. Dieback in the crown, usu- ture or semi-mature forest that may be unstable ally as a result of internal decay (root rots or other and often unable to adapt to the changed condi- fungal agents) has softened the center wood, tions fast enough, if at all. Such stands typically leaving a hard outer shell. The tops or branches suffer decline once isolated and often fail to pro- may be breaking off, and insect damage may be duce the benefits originally envisaged over longer evident. Primary cavity excavators move in and periods of time. new cavities appear annually. Foraging birds take To successfully implement an effective wild- advantage of the abundant insect life, while bro- life habitat plan, it is essential to have an inter- ken tops and limbs become nests and perching disciplinary approach, in which experts in all fields sites for raptors or other species such as owls. can freely discuss ideas and requirements at the A Class 3 tree is newly dead. The heartwood initial design stages—not at the last minute. In is usually hard, needles and twigs are still present, many cases, the planners can relax certain de- and the branches and bark are still intact. The velopment requirements to permit a slight den- roots are generally stable, but if root rot has killed 164 Dunster: Providing Wildlife Habitat in the Urban Forest

Stage 8 Stage 5 Stage 6 Stage 7 Stage 9 Stage 1 Stage 2 Stage 3 Stage 4 Down Declining Clean Broken Decomposed Stump Live Dead Loose bark material

Log decomposition Log decomposition Log decomposition Log decomposition Log decomposition class 1 class 2 class 3 class 4 class 5

Figure 2. The classification of wildlife trees and fallen logs. The illustrations shows a conifer; similar stages would be seen in deciduous trees (from Thomas 1979). the tree, this stability may be short lived. Class 3 the wood gets softer, nesting and shelter oppor- trees are used by primary cavity excavators as tunities for smaller mammals and amphibians in- well as secondary cavity users. The dead crease. branches are used for hunting and hawking A Class 6 tree has extensive internal decay perches, roosts, and large nests. As insect popu- and is starting to break up. The sapwood and lations increase, the tree will get more use from heartwood starts to fall off from the upper trunk foragers. area, the smaller roots have decayed, and the A Class 4 tree has no needles or twigs, and at larger roots are marginal. Cavity users no longer least 50% of the branches have been shed. The find it attractive habitat, but insect feeders, small heartwood is still reasonably hard, but the bark mammals, and amphibians may increase. is loose and the top may have fallen off. Cavity A Class 7 to 8 tree is in the final stages of excavators are still active, but weaker species decay. A stub of the tree remains, showing ex- are now able to dig out smaller cavities. The aban- tensive decay. A hard outer shell may remain, doned cavities are actively used by secondary but the softer central wood is almost completely cavity users, and bats and other insect feeders absent, and lateral roots are almost gone. At this are well established. stage, the tree is mainly used by amphibians, A Class 5 tree has decayed enough that it has small mammals, and insect-feeding birds. spongy heartwood. Most branches are lost, the Finally, a Class 9 tree is a stump or small stub. bark has fallen off, and internal decay is well ad- It provides good habitat for salamanders, small vanced. On a larger tree, the roots may still be mammals, and foraging birds, and may be used stable, but on smaller trees they may be ap- as a territorial marker or a drumming log for proaching instability due to decay. Cavity users grouse. It is also a nutrient source within the are still active, along with the insect feeders. As ecosystem. Journal of Arboriculture 24(3): May 1998 165

Decomposed fallen trees have well-defined are 15 to 20 m (50 to 66 ft) high, provide perch- characteristics, and distinct species use the logs. ing and nesting sites at the top and are already Figure 2 shows the correlation between wildlife being explored by woodpeckers for nesting and tree class and log decomposition class. forage. The cut top is notched and roughened In a natural forested ecosystem, there will usu- with a saw to provide a sufficiently rough base ally be an array of wildlife trees and fallen logs in for nest building. Under natural forces, the loss many different stages of decay and use (Parks of entire tree tops is common throughout the Pa- et al. 1997). In the managed ecosystem, many cific Northwest and up into British Columbia. of these wildlife attributes may have been lost. Douglas-fir and western hemlock are often seen With careful understanding of tree decay patterns as tall stumps with their entire crowns having been and of the manner in which wildlife use trees, ar- snapped off in heavy winds. Red alders and borists can help foster environmental benefits and bigleaf maple, known for their propensity to de- contribute to greater sustainability. cay from the top down, are common sites for cavity excavators. Creating Wildlife Trees Based on observations in the lower mainland As a part of a provincial strategy to retain suit- of British Columbia, it seems to take about 3 to 4 able wildlife habitat, foresters, biologists, and years before coniferous trees are first colonized government officials in British Columbia have by woodpeckers. Thereafter, colonization by other adopted the requirement for wildlife trees. Wild- species depends on rates of decay, but it seems life trees can be found in several forms. The most likely that many of these wildlife trees will remain obvious is the live tree in use by wildlife such as standing for 15 to 20 years before falling over. The raptors nesting in the crown (eagles, ospreys, and hardwood species decay faster, and crown dieback herons). If these trees are in active use by cer- and loss of the main scaffold takes place within tain species, they may be protected under wild- about 10 years. In several sites, the most life laws; the arborist should know and recognize hazardous trees have been converted into wildlife these trees and associated statutes. Whether a trees of varying heights, and the area is replanted tree is in active use is not always easy to ascer- to recreate a young forest. Careful extraction of tain, but local sources of knowledge, such as the tree tops, replanting, and retention of the nature clubs, local environmental organizations, understory where feasible, makes it possible to and government authorities can help. In many re-create habitat with good structural and biological cases, these trees will be designated as wildlife diversity—one that can support a wide array of trees once they have been documented. wildlife species for many years to come. A second form of wildlife tree creation is taking an existing hazard tree, cutting it off at some Other Issues with Wildlife Trees height above the ground, and then leaving it to In all of this work, safety must be considered. The decay. In other cases, trees have been removed current guidelines for wildlife tree retention in and then stuck back in the ground like giant posts British Columbia stipulate the creation of no-work (Bradford et al. 1996). zones around the tree, based on its condition, In British Columbia, it is now common to re- the degree of lean, and the slopes. This is gener- tain actively used wildlife trees, as well as to cre- ally fairly easy to comply with, although in areas ate new wildlife trees of varying heights. Some where a recreation trail passes close by, the man- are little more than small logs pushed into the ager of the area has to be fully aware of the snags ground and will never serve as good raptor or and undertake routine checks to ensure that they woodpecker trees. Many large trees, deemed too pose no hazard to pedestrians. In some cases, it tall and too unstable to safely retain, have been may require premature felling of the snags rather cut to a height at which they will not be a hazard than letting them progress through to their natu- to adjacent developments when such trees even- ral fall-down point. When a large tree cannot be tually fall down. These large trees, some of which retained, or when larger branches must be re- 166 Dunster: Providing Wildlife Habitat in the Urban Forest moved, it is often feasible—and ecologically valu- can actively promote these alternative practices able—to leave the larger chunks (the coarse and, over time, refine them. All of these small ef- woody debris) on the ground to decay. In such forts will help to make our urban forests more cases, these larger logs should be stable, which sustainable. usually requires all branches to be cut away so that the log sits right on the ground. It is also important to avoid using logs as bridges across Literature Cited creeks. Such a structure provides a tempting Agee, J.K. 1995. Management of greenbelts and forest challenge to adventurous youngsters, but may remnants in urban forest landscapes, pp 128-138. bring with it a liability issue that should have been In Bradley, G.A. (Ed.). Urban Forest Landscapes: avoided. Similarly, logs on slopes are best left Integrating Multidisciplinary Perspectives. pointing downhill, rather than sitting across the University of Washington Press. Seattle, WA. Backhouse, F. 1992. Wildlife Tree Management in slope. In the latter case, the log may roll and British Columbia. Ministry of Environment, Lands, cause a hazard and associated liability. and Parks, Victoria BC. Finally, there is always a question of how much Bradford, P., T. Manning, T, and B. I'Anson. (Eds.). clean-up should be undertaken. This will depend 1996. Wildlife Tree/Stand-level Biodiversity on the area, the species, and the goals of the Workshop Proceedings. Ministry of Forests and BC management plan. In an urban situation, it is gen- Environment, Victoria, BC. erally wise to clean up smaller branches and twigs Bradley, G.A. (Ed.). 1995. Urban Forest Landscapes: to reduce the potential for fire hazards. This ma- Integrating Multidisciplinary Perspectives. University of Washington Press, Seattle, WA. terial can be chipped on site and the mulch Bull, E.L., C.G. Parks, and T.R. Torgersen. 1997. Trees blown back in a thin layer. Avoid large mulch piles: and Logs Important to Wildlife in the Interior they might spontaneously ignite due to the heat Columbia River Basin. Gen. tech. rept. PNW-GTR- of decomposition or will decay anaerobically and 391. USDA Forest Service, Oregon. produce undesirable fermentation products. Bull, E.L., J.W. Thomas, and K. Horn. 1986. Snag Evenly distributed thin layers decay rapidly and management on the national forests in the Pacific help stabilize the forest floor. Northwest—1984. West. J. Appl. For. 1(2): The other consideration is pest problems. For 40-43. example, in British Columbia the Douglas-fir bark Chillibeck, B. (Ed.). 1993. Land Development Guidelines for the Protection of Aquatic Habitat. beetle is known to breed in the branch and twiggy Ministry of Environment, Lands, and Parks, material; cleaning and chipping this material re- Victoria, BC. duces the chances of creating a bark beetle Dunster, J.A. 1995. Effective tree retention in new epidemic. developments: An undisturbed landbase is the key Rather than completely removing the whole to success, pp. 125-131. In Neely, D., and G. tree, arborists can work with other professionals Watson (Eds.). Trees and Building Sites. to determine a safe height for a wildlife tree. Per- International Society of Arboriculture, Savoy, IL. haps only the top needs removing, or some of Dunster, J.A. 1996. Hazard tree assessments: the higher branches, or maybe the whole tree has Developing a species profile for western hemlock. J.Arboric. 22(1):51-57. to come down but the larger logs can be left on Dunster, J.A., and K. Dunster. 1996. Dictionary of site to decay slowly. Whatever the approach Natural Resource Management. UBC Press, adopted, arborists have an opportunity to expand Vancouver, BC. their own skills and play a useful role in helping Forestry Commission. 1990. Forest Nature create and maintain healthier urban forest eco- Conservation Guidelines. HMSO, London. systems. The key to success lies in taking an in- Forestry Commission. 1991. Community Woodland terdisciplinary approach and understanding the Design Guidelines. HMSO, London. role of trees in the ecosystem and how these func- Forman, R.T., and M. Gordon. 1986. Landscape tions can be incorporated into standard arbori- Ecology. Wiley, New York, NY. culture practices. With this knowledge, arborists Journal of Arboriculture 24(3): May 1998 167

Hodge, S.J. 1995. Creating and Managing Woodlands Rodwell, J., and G. Patterson. 1995. Creating New Around Towns. Forestry Commission Handbook 11. Native Woodlands. Forestry Commission Bulletin HMSO, London. 112. HMSO, London. Hudson, W.E. (Ed.). 1991. Landscape Linkages and Smith, D.S., and P.C. Hellmund. (Eds.). 1993. The Biodiversity. Island Press, Washington, DC. Ecology of Greenways: Design and Function of Kollin, C. (Ed.). 1994. Growing Greener Communities. Linear Conservation Areas. University of Minnesota Proceedings of the 6th National Urban Forest Press, Minneapolis, MN Conference. American Forests, Washington, DC. Thomas, J.W. (Ed.). 1979. Wildlife Habitats in Kollin, C. (Ed.). 1995. Inside Urban Ecosystems. Managed Forest: The Blue Mountains of Oregon Proceedings of the 7th National Urban Forest and Washington. Agriculture Handbook No. 553. Conference. American Forests, Washington, DC. USDA Forest Service, Washington, DC. Labaree, J.M. 1992. How Greenways Work: A Wildlife Tree Committee of British Columbia. 1992. Handbook on Ecology. National Park Service and Wildlife/Danger Tree Assessor's Course Work Atlantic Centre for the Environment, Ipswich, MA. Book. Ministry of Forests; Ministry of Environment; Machmer, M.M., and C. Steeger. 1993. The Ecological Workers Compensation Board of British Columbia, Role of Wildlife Tree Users in Forest Ecosystems. Victoria, BC. First Draft. Ministry of Forests, Prince George, BC. Maser, C. 1988. The Redesigned Forest. R. & E. Mills, Dunster & Associates Environmental San Pedro, CA. Consultants Ltd. Miliigan Raedeke, D.A., and K.J. Raedeke. 1995. P.O. Box 109 Wildlife Habitat Design in Urban Forest Landscapes, Bowen Island, BC pp 139-149. In Bradley, G.A. (Ed.). Urban Forest Landscapes: Integrating Multidisciplinary Canada VON 1G0 Perspectives. University of Washington Press, Seattle, WA. Ministry of Environment, Lands, and Parks. 1994. Stream Stewardship: A Guide for Planners and Developers. MOELP, Victoria, BC. Ministry of Environment, Lands, and Parks. 1995. Resumen. Los profesionistas de diseno, algunos arboristas y el publico en general, carecen de un Community Greenways: Linking Communities to entendimiento acerca de las funciones ecologicas de los Country, and People to Nature. MOELP, arboles para otros organismos, y como estas funciones y Victoria, BC. procesos ecologicos se conectan a traves de grandes Morrison, M.L., M.F. Dedon, M.G. Raphael, and M.P. extensiones en el paisaje. Consecuentemente, se pierden Yoder-Williams. 1986. Snag requirements of cavity- muchas excelentes oportunidades para la creacion y/o nestings birds: Are the USDA Forest Service retencion de habitats de vida silvestre en el bosque urbano. guidelines being met? West. J. Appl. For. 1(2): Algunas de estas oportunidades son discutidas, junto con ejemplos de la Columbia Britanica. Se incluye una seleccion 38-40. de literatura de aspectos relacionados, para proveer las Parks, C.G., E.L. Bull, and T.R. Torgersen. 1997. Field bases de lecturas adicionales y el entendimiento de la Guide for the Identifiaction of Snags and Logs in ecologia del paisaje, corredores verdes, arboles silvestres y the Interior Columbia River Basin. Gen. tech. rept. la manera como los arboristas pueden integrar estos PNW-GTR-390. USDA Forest Service, Oregon. principios dentro de sus practicas.