Arboriculture & Urban Forestry 36(6): November 2010 to 50% of the first 20 m. This finding is confirmed by another study that found a mean extent of encroachment of 16 m; how- ever, encroachment can be found up to 50 m of forest borders (McWilliam et al. 2010). This areal extent is significant within urban forests that tend to be small in area and narrow in diam- eter with high edge to interior ratios. Under these conditions, encroachment impacts would cover a large proportion of the total area of the forest. This areal extent of encroachment may also extend forest edge rather than interior conditions within larger urban forests, reducing the amount of habitat available to area and disturbance-sensitive species, such as neotropi- cal forest birds, which are uncommon within urban landscapes. Encroachment occurs at a high intensity in Ontario. Occurring frequently among edge residents, in 99% of sites. Encroachment also occurs frequently within the forest behind each residence, with a mean frequency of 23 traces (evidence of encroachment within quadrats) per residence. Encroachment types and behav- iors sampled suggest significant ecological impacts. For exam- ple, encroachment related to waste disposal, forest recreation, response to forest encroachment, and invasive yard plant exten- sions, often result in trampling impacts on soil structure and fer- tility (Malmivaara-Lamsa and Fritze 2003), the loss and degrada- tion of native vegetation communities (Florgard 2000; Murphy 2006), and may result in losses in local or regional native wild- life biodiversity (Friesen et al. 1995; Jokimaki and Huhta 2000). Their associated social and economic impacts may be even more significant to human communities. For example, yard extensions result in the loss of publicly-owned forest into private ownership, and the ecosystem services forests provide. Equitable access to these community resources is undermined with edge residents gaining greater access and use than residents living farther away. Waste disposal activities erode the aesthetics and recreational experience of the forest (Lynn and Brown 2003). Furthermore, these activities will lead to significant economic costs to commu- nities when municipalities increase active management resourc- es to reduce impacts to levels acceptable to their communities. Field observations and conversations with municipal staff sug- gested many encroachment impacts remain in place over long peri- ods. For example, conversations with municipal bylaw enforcement officers revealed many encroachments were difficult to remove once in place, particularly yard extensions (McWilliam 2009). Encroachment is also occurring within ecosystems that have low resistance and resiliency with respect to human activity impacts. Deciduous forests are among the least resilient to en- croachment because of their sensitive ground floras (Kuss 1986; Kuss and Hall 1991). Furthermore, encroachment activities are concentrated within the growing season when both vegetation and reproducing wildlife are at their most sensitive (Cole 2003). In forests adjacent to existing development, boundary treat- ments that reduce encroachment, active management (e.g., bylaw enforcement and monitoring), and resident education, could be im- plemented more frequently. In newly developing areas, effective land use planning that reduces the area of encroachment at coarse spatial scales could significantly reduce the need for expensive boundary structures and active management regimes, and may be more effective in protecting the features and functions of natural systems in the long term. Effective planning measures could in- clude: 1) protection of less vulnerable forests (e.g., larger in area with lower edge to interior ratios); 2) placing single-family resi- dential subdivisions adjacent to less sensitive, or more resilient, 259 natural systems; 3) altering the configuration of residential subdi- visions to reduce the length of forest edge exposed to encroach- ment, or 4) encouraging adjacent land uses more supportive to forested natural system features and functions. Further research is required to test the efficacy of these alternative strategies for lim- iting the area of encroachment impacts following development. LITERATURE CITED Braun-Blanquet, J. 1932. Plant Sociology: the Study of Plant Communi- ties. McGraw-Hill, New York. Brown, R.D., and T.J. Gillespie. 1995. Microclimatic Landscape Design. John Wiley & Sons, New York. Cole, D.N. 1987. Effects of three seasons of experimental trampling on five montane forest communities and a grassland in western Mon- tana, USA. Biological Conservation 40:219–244. Cole, D. N., and J.L. Marion 1988. Recreation impacts in some ripar- ian forests of the eastern United States. Environmental Management 12:99–107. Cole, D.N. 2003. Backcountry impact management: lessons from research. Trends 31(3):10–14. Correll, D.L. 1999. Vegetated stream riparian zones: their effects on stream nutrients, sediments and toxic substances. Report of Smith- sonian Environmental Research Center. Maryland, USA. Accessed October 18, 2002. Florgard, C. 2000. Long-term changes in indigenous vegetation pre- served in urban areas. Landscape and Urban Planning 52:101–116. Friesen, L.E., P.F.J. Eagles, and R.J. MacKay. 1995. Effect of residential development on forest-dwelling neotropical migrant songbirds. Con- servation Biology 9(6):1408–1414. Jokimaki, J., and E. Huhta. 2000. Artificial nest predation and abundance of birds along an urban gradient. Condor 102(4):838–847. Kaplan, S. 1995. The urban forest as a source of psychological well-being, In: G.A. Bradley (Ed.). Urban Forest Landscapes: Integrating Mul- tidisciplinary Perspectives. University of Washington Press, Seattle. Kent, M., and P. Coker. 1992. The description of vegetation in the field, pp. 20–38. In: Vegetation Description and Analysis: A Practical Ap- proach. Belhaven Press, London. Kuss, F.R. 1986. A review of major factors influencing plant responses to recreation impacts. Environmental Management 10:637–650. Kuss, F.R., and C.N. Hall. 1991. Ground flora trampling studies: five years after closure. Environmental Management 15:715–727. Lynn, N., and R.D. Brown. 2003. Effects of recreational use impacts on hiking experiences in natural areas. Landscape and Urban Planning 64:77–87. Malmivaara-Lamsa, M., and H. Fritze. 2003. Effects of wear and above ground forest site type characteristics on the soil microbial commu- nity structure in an urban setting. Plant and Soil 256:187–203. Matlack, G.R. 1993. Sociological edge effects: spatial distribution of hu- man impact in suburban forest fragments. Environmental Manage- ment 17:829–835. McWilliam, W.J. 2009. The Housing/Forest Interface: Structural Approaches for Protecting Suburban Natural Areas Post Develop- ment. VDM Verlag Dr. Muller, Saarbrucken, Germany. McWilliam, W.J., P. Eagles, M. Seasons, and R. Brown. 2010. The hous- ing/forest interface: testing structural approaches for protecting sub- urban natural systems following development. Urban Forestry and Urban Greening 9:149–159. ©2010 International Society of Arboriculture
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