254 McWilliam et al.: Degradation Effects of Local Residents on Urban Forests In terms of areal extent, studies indicate residential en- croachment impacts are concentrated within forest edges rather than uniformly distributed in the forest (Matlack 1993; Mc- William et. al. 2010). Matlack (1993) surveyed 95% of both yard and recreation related impacts within 67 m of forest bor- ders within forests without internal roads; while McWilliam et al. (2010) surveyed 95% of residential impacts within 34 m within forests abutting contiguous single-family housing (with gross densities of 5 to 19 houses per hectare). However, the area of the forest floor covered by encroachment within this distance within Southern Ontario municipalities is unknown. According to boundary theory, the condition of the boundary of a natural system indicates its overall health (Schonewald-Cox 1988). Thus, it is important to retain its integrity to protect the more sensitive features and functions occurring within the forest interi- or. According to Schonewald-Cox (1988), the extent to which an ecosystem boundary is protected from adjacent land use impacts is dependent on: 1) efficacy of its natural filters (e.g., a closed side canopy reduces the extent of edge generated by a change in micro- climate between a forest and open field, and is therefore a natural filter for limiting microclimatic impacts); 2) efficacy of human- generated filters (e.g., fences for limiting encroachment impacts); 3) extent to which filters are upheld (e.g., through encroachment bylaw enforcement); 4) similarity between adjacent ecosystems, and 5) similarity between land use values and objectives of adja- cent landowners. Schonewald-Cox (1988) argues that a loss of, or reduction in, one of these factors will require an increase of those remaining if the integrity of the boundary, and therefore the natu- ral system, is to be protected through time. Otherwise, features and functions of the boundary, and therefore the ecosystem, will change to become more similar to those of the adjacent land use. Ontario governments have developed planning and manage- ment policies and practices in support of their urban forested eco- systems to ensure their long-term protection. While Ontario mu- nicipal planners and managers recognize that impacts will occur with adjacent development, they want to ensure impacts are kept to acceptable limits (McWilliam 2009). To accomplish this, mu- nicipal planners and managers rely on boundary-focused, passive management measures, such as fences, and/or active management measures, such as boundary monitoring, bylaw enforcement, and resident education (McWilliam 2009). Some planners and man- agers recognize encroachment occurs with this strategy; howev- er, they do not know whether it is substantial enough to warrant changing, or increasing resources or strategies (McWilliam 2009). The goal of this paper was to assess the degradation ef- fects of encroachment within Ontario urban forest edges. This was accomplished by determining the area of the forest floor affected by adjacent residents’ encroachment activities. METHODS Study Areas Human impacts were sampled behind 186 residential proper- ties within 40 forest fragments in six municipalities of Southern Ontario, including Cambridge, Guelph, Kitchener, Mississauga, Oakville, and Waterloo. Municipalities range in population be- tween 100,000 to 700,000 and are in the Greater Toronto Area (Figure 1). All of these municipalities are implementing bound- ary treatments as passive management in some forests and/ ©2010 International Society of Arboriculture Figure 1. Study municipalities in Ontario, Canada. Image courtesy of the Ontario Ministry of Natural Resources (2002). or active management that may include boundary monitoring, bylaw enforcement, or resident education (McWilliam 2009) Most study forests were remnants of deciduous, but a few were mixed, eastern forest patches or corridors. They ranged in size between 1 and 50 hectares in area, without internal roads, and had minimum widths of 20 m. However, if there was devel- opment on the opposing side of the forest, then the minimum width was 40 m. This reduced the risk of sampling opposing resident encroachment and responds to results of a pilot study (McWilliam 2009) indicating a majority of encroachment oc- curred within 20 m of forest borders. To avoid overlapping hu- man activity impacts associated with community recreation, authorized recreational trails had to be located a minimum of five meters away from study areas. Research indicates the area of impact associated with recreational trail use is approxi- mately five meters from trail edges (Cole 1987). Sites adjacent to park entry points were not sampled to avoid sampling of en- croachment arriving from other residences in the community. Forest borders were without significant natural barriers that could serve as natural filters to encroachment (e.g., steep slopes, poorly drained soils). Abutting housing was typical of post World War II housing within Southern Ontario, consisting of single- family, contiguous and detached, or semi-detached, with back- yards. Gross housing densities were between 5 and 19 houses per hectare. Housing was at least 10-years-old. Recreation ecology research indicated maximum impacts of recreational activities oc- curred in forests within two to five years of their commencement (Cole 1987). Back yards were between 10 and 40 meters in width. Sampling Methods The frequency and percentage area of the forest floor covered by encroachment activities were sampled using a quadrat/transect sampling method. The use of quadrats and transects are commonly used to sample forest vegetation (Kent and Coker 1992). Recre- ation ecology research commonly measures recreational tram- pling impacts on vegetation communities using this method (For example, Cole & Marion 1988). The quadrat/transect sampling method requires the researcher to visually estimate the percentage of a sample area occupied by components of the forest floor. In urban forest edges, component categories include native, naturally occurring elements (such as native plants, soils, or woody debris),
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