Arboriculture & Urban Forestry 36(6): November 2010 Arboriculture & Urban Forestry 2010. 36(6): 253-260 253 Assessing the Degradation Effects of Local Residents on Urban Forests in Ontario, Canada Wendy McWilliam, Paul Eagles, Mark Seasons, and Robert Brown Abstract. Urban forests provide essential social, ecological, and economic functions in support of their communities; however, surveys indicate adjacent residents conduct activities within their yards and the adjacent public forest edge that degrade these systems. Local governments rely on boundary-fo- cused passive management and/or active management to limit impacts. Encroachment results from various boundary treatments; however, it is not known whether encroachment represents a substantial source of degradation within Ontario, Canada, municipal forests. To evaluate this, percentage cover of encroachment impacts adjacent to 186 homes within 40 forests of six Southern Ontario municipalities was surveyed. The results indicated degradation re- sulting from encroachment was substantial. Encroachment occurred in highly valued and sensitive ecosystems, and during sensitive time periods. This was highly prevalent and covered a substantial proportion of the forest edge. Some encroachment behaviors were particularly harmful, resulting in the loss of significant forest area to residential land uses. Furthermore, encroachments remained over long periods. The small sizes and convoluted shapes of urban forests leave them vulnerable to these impacts. Prevailing municipal strategies are insufficient to protect these systems from encroachment. To ensure their long term protection, municipalities and their communities need to substantially increase their commitment and resources for addressing encroachment. Key Words. Adjacent Land Use; Green Infrastructure; Greenspaces; Planning and Management; Residential Encroachment; Urban Forest Ecosys- tems; Urban Forest Edges. Urban forest ecosystems provide essential ecological and so- cial services to human communities. They provide stormwater management (Correll 1999), filter air-borne pollutants (Scott et al. 1999), reduce the rate of climate change (Nowak and Crane 2002), and moderate extreme weather conditions, im- proving human thermal comfort (Brown and Gillespie 1995). Furthermore, these ecosystems provide key recreation facil- ities in support of human health (Kaplan 1995). Many studies have looked at the impacts of human activities, and housing areas in general, on urban forests. Key impacts include reductions in soil organism diversity and soil fertility (Malmivaara- Lamsa and Fritze 2003), and local and regional native vegetation diversity resulting from human trampling of soils and vegetation (Florgard 2000; Murphy 2006). Reductions in local and regional native wildlife diversity resulting from human disturbance and wildlife habitat alteration may also occur (Friesen et al. 1995; Joki- maki and Huhta 2000). Furthermore, the recreational experiences of these areas are degraded through the proliferation of litter, tree and plant damage, fire rings, and unauthorized trail creation (Lynn and Brown 2003). Residential encroachment refers to the impacts on natural areas resulting from adjacent resident activities within their yards and in the forest edge. Some studies indicate encroach- ment results in impacts similar to those occurring with recreation- related activities (Matlack 1993; McWilliam 2009); however, other impacts are unique and more serious, such as the loss of public forest edge to private residential land uses (McWilliam 2009). Because of the similarity between impacts of recreation and encroachment, recreation ecology theory regarding factors determining their significance can be loosely applied. Recre- ation ecology studies indicate the significance of human ac- tivity impact is determined by the impact characteristics (its areal extent, longevity, and its intensity of impact), and the ecosystem attributes (i.e., the human value placed on the eco- system) (Cole 2003). Intensity of impact is in turn determined by the frequency and type of use, how it occurs, the season in which it occurs, and the ecosystem sensitivity (Cole 2003). Progress has been made in defining factors that determine the significance of residential encroachment within urban forests. In terms of intensity, studies have identified the types of encroach- ment. For example, Matlack (1993) surveyed 14 types, and Mc- William et. al. (2010) surveyed 20 farthest from forest borders. Types reflected waste disposal, yard extension, unauthorized for- est recreation activities, invasive yard plant extensions, as well as behaviors in reaction to forest encroachment into residential yards (e.g., removal of forest border vegetation over-arching residential yards) (McWilliam et al. 2010). Encroachment stud- ies within Southern Ontario have taken place in mixed, and par- ticularly deciduous, urban forests (Taylor 1992; Ouellet 1996; McWilliam 2009), and publicly-owned mown grass strips ly- ing between residential property lines and forest borders (Mc- William et al. 2010). Forested ecosystems, particularly decidu- ous forests, are among the more sensitive ecosystems to human activity impacts because of their sensitive ground floras (Kuss and Hall 1991). Little is known about why encroachment activi- ties occur, or the frequency at which residents perform them. ©2010 International Society of Arboriculture
November 2010
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