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Effectiveness of boundary structures in limiting residential encroachment 1 into urban forests 2
______________________________________________________________________ 3 4 ABSTRACT /Urban forests provide essential functions in support of their human communities; 5
however, studies indicate adjacent residential land uses degrade these natural systems following 6
development. Local Ontario governments rely primarily on passive management, such as 7
boundary-focused measures (e.g. fences) to limit this degradation but, it is not known whether 8
these measures are effective for limiting the area of the forest floor covered by encroachment 9
impacts. Transect and quadrat sampling of 40 forest edges adjacent to 186 residential properties 10
were sampled in six Southern Ontario municipalities to determine the frequency and area cover 11
of encroachment impacts. The results indicated some boundary structures are effective in 12
reducing the frequency and area cover of some encroachment behaviours but, the area covered 13
by some behaviours of encroachment were not reduced, some were actually increased by 14
boundary measures, and substantial areas of encroachment continued to occur under even the 15
most effective boundary treatments. The most effective boundary treatment in this study was 16
ungated fencing in combination with a mown strip which was found to reduce the incidence of 17
yard extension and concentrated the encroachment closest to the forest edge. 18
Key words: Green infrastructure; Greenways; Residential encroachment; Urban natural systems 19 planning and management; Urban forest edges 20
1.0 Introduction 21
Urban natural systems are essential elements in the provision of urban ecological services 22
to human communities. They provide storm water management (Correll, 1999); filter pollutants 23
from the air (Scott et al., 1999); sequester carbon, reducing the rate of climate change (Nowak 24
and Crane, 2002), and moderate extreme weather conditions, improving human thermal comfort 25
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(Brown and Gillespie, 1995). Furthermore, they provide key recreation facilities in support of 26
human health (Faber-Tayler et. al., 2001; Wells, 2000; Kaplan, 1995). 27
There is increasing evidence of adjacent residential land uses degrading urban natural 28
systems, particularly woodlands, following development within central Canada (Ouellet, 1996; 29
Taylor, 1992; McWilliam, 2009) and in the northeastern U.S. (Moran, 1984; Matlack, 1993). The 30
impacts of these adjacent land uses are collectively referred to as encroachment. Direct 31
encroachment occurs with residential activities in adjacent publicly-owned forest edges (e.g. 32
private garden extensions). Indirect forms occur with activities in residential yards (e.g. garden 33
plant invasions of forest edges from residential yards). 34
Ontario municipal planners and managers recognize that some impacts to natural systems 35
will occur with adjacent development. However, they want to ensure impacts are kept to 36
acceptable limits, and have developed planning and management policies and practices to ensure 37
their features and functions are protected for the long-term (McWilliam, 2009). They have relied 38
on boundary-focused measures in planning policies, such as requiring the installation of fences 39
and buffers, and infrequently implemented management measures, such as bylaw enforcement, 40
boundary monitoring and resident education (McWilliam, 2009). However, municipalities know 41
relatively little about the effectiveness of this strategy, or the relative effectiveness of boundary-42
focused planning or management measures for limiting encroachment impacts on their natural 43
systems. 44
Different types of encroachment results in different impacts. Exotic garden plant 45
extensions, and human trampling and disturbance within forest edges resulting from other 46
encroachment activities often result in a reduction in native shade-tolerant plant species, and an 47
increase in the number of exotic and native light and disturbance-tolerant plant species that can 48
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in turn lead to reductions in local and regional native plant diversity (Bagnall, 1979; Florgard, 49
2000; Hoehne, 1981; Manning, 1979; McWilliam, 2009). 50
The impacts of other indirect forms of encroachment, such as alterations in noise, light, 51
hydrological and chemical regimes, or pet predation of wildlife within forested ecosystems are 52
less visually apparent , and therefore more difficult to measure. Individual impacts may take 53
years to accumulate before serious impacts become apparent and they can be measured (Murphy, 54
2006). Furthermore, impacts are often complex and species dependent. For example, studies 55
indicate that excessive chemical, particulate or bacteria flows from adjacent urban land uses into 56
natural system soils and water bodies can lead to the anatomic alteration of frogs (Mayer et al., 57
1999; Reeder et al., 2005; U.S. Environmental Protection Agency, 1995), and the alteration of 58
fungi and invertebrates within soils and water contaminated with these substances can in turn 59
lead to alterations in plants and animals (Cousins et al., 2003), and may impact human health. 60
Most direct behaviours of encroachment are much more obvious and measurable. The 61
impacts of some behaviours, such as the extension of residential lawns and gardens, are 62
particularly striking and can result in the long term loss of public forest area to private land uses 63
(McWilliam, 2009). Many direct forms of encroachment result in ecological and recreation 64
impacts similar to those experienced within forests of less developed landscapes. Recreation 65
ecology studies indicate that hiking and result in the trampling and disturbance of soils, 66
vegetation and wildlife, and degradation of recreational experience (Cole, 1987; Manning, 1979; 67
Farrell and Marion, 1998; and others). Similar, but more intensive, human activities within urban 68
forests, commonly referred to as passive recreation, result in similar impacts. Trampling can 69
negatively impact soil fertility, and reduce soil organism diversity (Malmmivaara-Lamsa and 70
Fritze, 2003 ). It also negatively impacts vegetation communities (Florgard, 2000). Furthermore, 71
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human disturbance of wildlife and alteration of wildlife habitat can reduce native wildlife 72
communities and diversity (Sauvajot et al., 1998). Human activities such as waste disposal, tree 73
and plant damage, fire ring and unauthorized trail creation can also degrade the quality of 74
recreational experience (Lynn and Brown, 2003). Many direct forms of encroachment result in 75
similar impacts (Matlack, 1993; Ouellet, 1996; Taylor, 1992; McWilliam, 2009; McWilliam et 76
al., 2010). 77
Extensive recreation ecology studies have identified the factors contributing to the soil, 78
plant, wildlife and recreation experience impacts of human activities that result in trampling and 79
disturbance, and managers of these landscapes use their understanding of these factors to 80
develop effective mitigation strategies. Factors include the characteristics of the impact (its areal 81
extent, longevity, and the intensity of impact) and the attributes of the ecosystem (i.e. the human 82
value placed on the natural system in which the impact takes place (Cole, 2003). Intensity of 83
impact is in turn determined by the frequency of use, the type of use and how it occurs, the 84
season in which it occurs and the sensitivity of the ecosystem to the impact (Cole, 2003). 85
Managers of some of the larger U.S. and Canadian national parks have developed 86
strategies that manipulate many of these factors through time, and at different spatial scales (for 87
example, Leung and Marion, 1999; USDI National Park Service, 1997), focusing their resources 88
on factors that have the greatest potential to reduce impacts. However, in general, the results of 89
recreation ecology studies looking at the relative efficacy of the different factors contributing to 90
the significance of human activity impacts, indicate that reducing the spatial extent over which 91
impacts occur is particularly important in reducing the significance of human activity impacts 92
(Cole, 2003, and others). Applied to the reduction of similar encroachment-related impacts, this 93
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suggests that strategies that controlling the area in which encroachment occurs are likely to be 94
more effective than those seeking to reduce the intensity (e.g. frequency) of impacts. 95
In terms of areal extent of encroachment, at coarse spatial scales, studies indicate 96
residential encroachment is highly prevalent within Southern Ontario municipal forests, 97
occurring in 100% of municipalities surveyed and adjacent to 95% of residential yards 98
(McWilliam et al., 2010). At the scale of the individual forest, encroachment tends to be 99
concentrated within forest edges rather than uniformly distributed throughout the forest 100
(Matlack, 1993; McWilliam et. al., 2010). For example, Matlack (1993) surveyed 95% of both 101
yard and recreation related impacts within 67 metres of forest borders in forests without internal 102
roads; while McWilliam et al. (2010) surveyed 95% of residential impacts along within 34 103
metres of forest borders adjacent to abutting and contiguous single-family housing (with gross 104
densities of 5 to 19 houses per hectare). Studies also indicate some boundary structures that 105
control physical access, delineate private from public land uses and encourage boundary 106
monitoring significantly reduce the maximum distance from forest borders in which 107
encroachment occurs. However, the area of the forest floor covered by encroachment within this 108
distance and the effectiveness of boundary measures for reducing this encroachment area are 109
unknown. 110
This paper investigated the relationship between boundary treatment and the 111
encroachment area of forest edge behind residential properties. The results will assist planners 112
and managers in developing more effective approaches for limiting encroachment impacts within 113
municipal forested natural systems. 114
115 2.0 Methods 116 117 2.1 Study areas 118
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119 Human impacts were sampled behind 186 residential properties within 40 forest 120
fragments within six municipalities of Southern Ontario, including Cambridge, Guelph, 121
Kitchener, Mississauga, Oakville and Waterloo. Study municipality populations range between 122
100,000 to 200,000, with the exception of Mississauga, with a population of 700,000, and are 123
situated within the Greater Toronto Area (Figure 1). All are currently implementing boundary 124
treatments as a passive management measure to limit encroachment, and are infrequently 125
implementing active management measures including boundary monitoring, bylaw enforcement 126
and resident education (McWilliam, 2009). 127
128 Figure 1. Study municipalities in Southern Ontario, Canada 129
(Source: (Ontario Ministry of Natural Resources, 2002)). 130 131
Most study forests were remnants of upland deciduous eastern forests. A few were mixed 132
deciduous/coniferous upland eastern forest fragments, or were lowland deciduous eastern forest 133
corridors. Fragments were between 1 and 50 ha in area, without internal roads, and had minimum 134
widths of 20 metres (if there was no development on the other side of the forest). If there was 135
opposing development, then the minimum width was 40 metres. This site selection criterion 136
reduced the risk of sampling opposing resident encroachment and responds to results of a pilot 137
study (McWilliam, 2009) indicating a majority of edge-resident encroachment occurred within 138
20 metres of the property boundary. To avoid overlapping encroachment associated with 139
community recreation authorized recreational trails had to be located a minimum of five metres 140
away from study areas. Research indicates that the area of impact associated with recreational 141
trail use is approximately five metres from the trail edge (Cole, 1987). Furthermore, sites 142
immediately adjacent to park entry points were not sampled to avoid the sampling of 143
encroachment activities arriving from other residences in the community. 144
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Forest borders were without significant natural barriers to human entry (such as dense, 145
prickly, or poisonous vegetation, steep slopes, or poorly drained soils). Adjacent housing was 146
typical of post World War Two suburban housing within Southern Ontario, consisting of single-147
family, contiguous and detached or semi-detached, with backyards. Gross housing densities were 148
between 5 and 19 houses per hectare. Housing was at least 10 years old. Research had indicated 149
that maximum intensities of the most visible effects of recreational activities, such as loss of 150
organic soils, erosion, and changes in vegetation communities occurred in forests within two to 151
five years of the occurrence of recreation activities resulting in trampling (Cole, 1987). Back 152
yards were between 10 and 40 metres in width and directly abutted municipal natural area 153
boundaries. 154
2.2 Measures for limiting encroachment 155 156 2.2.1 Passive management measures 157 158 Municipal environmental planners and forest managers within the study municipalities 159
indicated they had implemented two boundary-focused passive management treatments within 160
sites meeting the above site selection criteria: 1) fence (installed on municipal land) and 2) 161
boundary demarcation post (installed on municipal land). However, the pilot study (McWilliam, 162
2009) indicated that a majority of forests with adjacent residential neighbourhoods within 163
Southern Ontario municipalities had a wide variety of both residential and/or municipality-164
installed boundary treatments. Encroachments occurring under eight of these additional 165
boundary treatments were sampled. These boundary treatments consisting of: 1) no or minimal 166
boundary demarcation (e.g. a flower bed), 2) grass strip, 3) grass strip and path, 4) fence and 167
grass strip, 5) fence, grass strip and path, 6) fence with gate, 7) fence with gate and grass strip, 168
and 8) fence with gate, grass strip and path. Sites adjacent to resident-installed fences as well as 169
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municipal fences were sampled in order to determine whether there was a significant difference 170
in encroachment between resident and municipality-installed fences. Some of the municipal 171
components within boundary treatments were not implemented to reduce encroachment, but to 172
provide recreational facilities or maintain utility corridors. Table 1 summarizes the boundary 173
treatments surveyed, their ownership and whether they were implemented to address 174
encroachment. 175
Table 1. Evaluated boundary treatments 176
Grass strips were a maximum of 50 metres in width (the average width was 20 metres). 177
Only sites with mown grass strips were selected for sampling because the pilot study 178
(McWilliam, 2009) indicated long grass or shrubs within the grass strip could alter encroachment 179
behaviours. Paths were located adjacent to, or within, grass strips, and ran roughly parallel to 180
residential property boundaries. 181
182 2.2.2 Active management measures 183 184 Municipal environmental planners and forest managers within the study municipalities 185
indicated all study municipalities implemented management measures to limit encroachment, but 186
infrequently and informally (McWilliam, 2009). Within study sites measures consisted of the 187
enforcement of bylaws prohibiting encroachment activities, the informal municipal and/or 188
community monitoring of boundaries and the installation of signs prohibiting the dumping of 189
resident waste. Municipal staff and available records indicated bylaws had been implemented 190
within 11 of the 186 (6%), study sites. Signs at park entries prohibiting the dumping of waste 191
were primarily installed within park entrances of 16 of the 40 (40%), study forests. There were 192
no records of municipal monitoring of boundaries; however, staff from five out of six 193
municipalities indicated that municipal monitoring of boundaries occurred infrequently, and not 194
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more than once per year. The exception was Oakville where municipal staff indicated regular 195
municipal monitoring of boundaries occurred within sites with boundaries consisting of a fence, 196
grass strip and a path. 197
198 2.3 Sampling methods 199 200 The frequency and percentage area of the forest floor covered by encroachment activities 201
were sampled using a quadrat/transect sampling method. The use of quadrats and transects are 202
commonly used to sample forest vegetation (Kent and Coker, 1992). Recreation ecology research 203
also commonly measures the impacts of recreational trampling on vegetation communities using 204
this method (For example, Cole and Marion, 1988). The quadrat/transect sampling method 205
requires the researcher to visually estimate the percentage of a sample area occupied by different 206
components of the forest floor. In urban forest edges, component categories include native, 207
naturally occurring elements (such as native plants, soils or woody debris), exotic vegetation 208
(arriving via other means than from adjacent residential yards), and encroachment elements or 209
traces (e.g. construction waste, lawn extensions, unauthorized pathways or plants originating 210
from residential yards). Within each ½ metre2 quadrat sampled, we recorded the percentage 211
cover of the quadrat of each of these components visible at 30 cm above the ground, according to 212
the Braun-Blanquet (1932) abundance-cover scale. The scale assigns a number, or code, to each 213
forest floor component, ranging from 0 to 6 (Table 2). 214
215 Table 2. Braun-Blanquet (1932) abundance-cover scale 216
217 The frequency in which encroachment occurred was calculated by counting the number 218
of times one type of encroachment appeared within the quadrat, no matter what percentage of the 219
quadrat it covered. The sample design was perfected during the pilot study to capture the breath 220
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and depth of encroachment activities under different boundary conditions (McWilliam, 2009). 221
Eleven 0.5m by 0.5m quadrats were sampled at two-metre intervals along five transects placed 222
perpendicular to, and equal distance along, property boundaries. From the property boundary, 223
transects extended 20 metres into forest edges. The first and last transects were placed one metre 224
from neighbouring property boundaries to reduce the risk of recording neighbouring 225
encroachment. This design resulted in 55 samples per site, for a total sampling intensity of 930 226
transects and 10,225 samples (Figure 2). 227
228 Figure 2. Quadrat/Transect sampling design for one study site 229
230 Care was taken to record only types of encroachment associated with adjacent study 231
residents. For example, cut trees were not recorded since resident-cut trees could not be 232
distinguished from municipally cut, or hazardous, trees. In addition, evidence of old dumps, rock 233
piles, and old fencing, were not recorded as they may be from previous agricultural land uses. 234
Categories of encroachment were developed in order to analyze the significance of 235
different encroachment behaviours within the forest edge in response to boundary treatments. 236
Categories of encroachment were developed from the types and spatial patterns of encroachment 237
in forest edges in relation to yard activities and patterns revealed in the pilot study (McWilliam, 238
2009). Municipal forest managers, bylaw enforcement officers, and casual conversations with 239
residents verified these behaviours. 240
Behaviours identified include: 1) waste disposal, 2) yard extension, 3) forest-recreation, 241
4) response to forest encroachment and 5) yard plant invasions. Disposal behaviour results in 242
yard or house-related waste being dumped within forest edges, including construction debris, 243
grass clippings, or miscellaneous organic waste. The yard extension category of encroachment 244
includes any extensions of private yard-related land uses within the public forest edge, including 245
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lawn extensions, or the installation of recreational equipment such as trampolines or swimming 246
pools. The forest recreation category of encroachment includes types of encroachment that result 247
in private, forest recreation-related facilities within the forest edge, such as children's forts, fire 248
pits or private entry pathways. Yard plant invasion encroachments result in garden plants 249
growing within the forest edge. Exotic plants growing in the forest edge, but not typically grown 250
in residential gardens, are not included within this encroachment category. Residential 251
encroachment in response to forest encroachment refers to encroachment activities that respond 252
to forest components (e.g. vegetation or wildlife) encroaching into their yards. An example of 253
encroachment resulting from this behaviour is the resident removal of forest border vegetation 254
extending over property boundaries. 255
256 3.0 Data Analysis 257 258
Null hypotheses of uniform distribution within the forest of all encroachment traces, 259
encroachment traces by behaviour, and encroachment traces by boundary treatment were tested 260
using a Kolomogorov-Smirnov test. 261
The frequency of traces and the percentage of the sampled forest floor covered by traces, 262
was calculated for all encroachment occurring, as well as by type and behaviour of 263
encroachment. In addition, an indicator of the relative significance of encroachment was 264
calculated by multiplying the mean frequency of traces (number of areas of encroachment) by 265
the mean Braun-Blanquet abundance-cover scale representing the percentage area covered within 266
the sample area. For example, if a yard extension encroachment trace was sampled three times in 267
a site (i.e. in three different quadrats) and covered 75 to 100% of the quadrat (a Braun-Blanquet 268
abundance cover scale of 6), then the indicator of encroachment significance for this site 269
(heretofore referred to as indicator) would be 18. 270
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Frequencies of traces and significance of encroachment by type, behaviour and with 271
distance from forest borders were also calculated for each boundary treatment to determine the 272
relative efficacy of boundary treatments for limiting encroachment. Kolomogorov-Smirnov two-273
sample tests were conducted to determine the extent to which boundary treatments significantly 274
altered mean frequencies and indicators of encroachment. A Kruskal-Wallis test was conducted 275
to determine whether the ownership of the boundary treatments (i.e. municipality or resident 276
owned) significantly altered mean frequencies and indicators of encroachment. We also 277
conducted a Spearman correlation test to determine whether fence height significantly altered the 278
frequency and percentage cover of encroachment. 279
4.0. Results 280 281 4.1 What is the mean frequency and percentage cover of encroachment under different 282 boundary treatments? 283 284 Encroachment activities occurred within sites under all boundary treatments; however, 285
there was a significant difference in mean frequency and mean indicators between boundary 286
types (P<.05). Boundary treatments discouraging resident access to forest borders had 287
significantly lower frequencies and indicators than treatments allowing access. Fences were 288
effective in discouraging access to forest edges, functioning to decrease the area cover of the 289
forest floor covered by encroachment. Boundary treatments with fences (no gates) had 290
significantly lower mean frequencies and indicators than boundary treatments without fences, or 291
those having gates (P < .05). For example, the forest floor covered by encroachment traces 292
increased from 26 -50% in fenced sites to 51 -75% in fenced sites with gates. There was no 293
significant difference in the mean frequency or mean indicator between sites having municipal 294
fences and sites having resident fences (P >.05). 295
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Sites having no boundary demarcation had significantly higher frequencies and 296
indicators than all other boundary treatments, except sites with grass strips (P < .05). In addition 297
to their lack of elements deterring resident entry to forest edges, many sites with no boundary 298
demarcation lacked any official property line demarcation. For example, only 30% of sites with 299
no boundary treatment had a survey stake. However, in many cases survey stakes did not appear 300
to reduce encroachment activities. For example, Figure 3 illustrates a garden extension 301
encroachment within a site subject to a municipal boundary post and survey stake. 302
303 Figure 3. Yard extension encroachment (highlighted in light green) 304
despite a municipal boundary post (marked with an 'x') and survey stake (bottom left) 305 (Photo: Sugar bush Park, Waterloo. Source: McWilliam, 2004) 306
307 When grass strips, with and without paths, were added to fences, the frequency and 308
indicator were significantly less than those of sites having just a fence (P<.05). This suggests that 309
grass strips and paths combined with fences provide more barriers to encroachment behaviour 310
than fences alone. 311
Municipal boundary posts were not highly visible to residents and did not physically 312
deter residents from entering forest borders. Yet, sites with municipal boundary posts had 313
significantly lower mean frequency and indicator than sites with no municipal boundary 314
demarcation policy, fenced sites with gates, and fenced sites (P<.05). These findings may have 315
been due to site-specific factors, since only 12 sites with this boundary type were available for 316
sampling, and most were located in one municipality. Within many of these sites, the adjacent 317
houses were built without removing forest vegetation from resident yards, and some residents 318
retained the forest floor vegetation following development (Figure 4). In addition, shaded 319
conditions, created by overhanging forest canopy trees, may have deterred residents from 320
establishing lawns thereby discouraging yard extension encroachments. 321
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322 Figure 4. Low levels of encroachment where residents retained native forest floor 323
cover despite a subtle boundary treatment that did not deter residents 324 from entering the forest border 325
(Photo: Sparrow Park, Waterloo. Source: McWilliam, 2005) 326 327
328 4.2 Was there a significant difference in the frequency and indicator of significance of 329 encroachment with respect to the distance from the forest border? 330 331 The frequency and indicator of encroachment intensity occurring within sites with fence 332
components (without gates) appeared to be distributed closer to forest borders than that occurring 333
within sites without fences, and within sites having fences and gates. For example, 95% of 334
encroachment traces were located within 16 metres of fenced sites, but were located within 18 335
metres in fenced sites with gates, and 20 metres within sites with no boundary treatment. 336
However, the difference in distribution was not statistically significant. 337
338 4.3 What was the mean frequency and intensity of different encroachment behaviours 339 under different boundary treatments? 340
341 4.3.1 Yard extension encroachment 342 343
Boundary treatments that included a fence (but not a gate) had significantly lower 344
frequencies and indicators of yard extension encroachment than sites without fences or fenced 345
sites with gates (P < .05). For example, the mean indicator of yard extension increased from 10 346
in fenced sites to 35 in fenced sites with gates. The percentage of the forest floor covered by yard 347
extensions increased from a mean of 51 to 75% in fenced sites, to 76 to 100% in fenced sites 348
with gates. Furthermore, the frequency at which yard extension encroachment was sampled 349
increased three fold between the two boundary treatments. Figures 5 and 6 illustrate the 350
differences in the mean indicators of encroachment behaviours between fenced and fenced sites 351
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with gates with respect to forest borders. Notice the dramatic increase in mean indicator of yard 352
extension intensity between the two boundary treatments. 353
354 Figure 5. Distribution of mean indicators of significance of encroachment 355
behaviours with respect to distance from forest borders in fenced sites. 356 357 358
Figure 6. Distribution of mean indicators of significance of encroachment 359 behaviours with respect to distance from forest borders in fenced sites with gates. 360
361 Sites with grass strips (and no gate) appeared to have lower mean frequency of yard 362
extension encroachment and indicators of yard extension intensity than boundary treatments 363
without grass strips. In fact, many of these boundary treatments, such as fences, grass strips and 364
paths had no yard extension traces within the forest edge. However, relatively few sites with 365
grass strips were sampled due to lack of availability, and these relationships were not statistically 366
significant. Nevertheless, grass strips appeared to deter yard extensions within forest borders and 367
encourage them within grass strips (Figure 7). 368
369 Figure 7. Grass strips appear to encourage yard extensions within grass strips 370
(flowerbed to left of measuring tape) rather than forest edges 371 (Photo: Anndale Park, Waterloo. Source: McWilliam, 2005) 372 373 4.3.2 Waste disposal encroachment 374 375
None of the boundary treatments eliminated waste disposal encroachment behaviour. 376
Sites with grass strips significantly reduced waste disposal mean frequency and indicators 377
relative to sites without grass strips (as long as there were no gates) (P < .05). The appearance of 378
gates within boundary treatments with grass strips led to a significant increase in waste disposal 379
encroachment relative to sites having grass strips, but no gates (P < .05). Figure 8 illustrates the 380
distribution of waste disposal encroachment behaviour with respect to distance from forest 381
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borders within sites with fences, grass strips and paths. Notice the lower waste disposal 382
encroachment relative to those within sites with just fences or fences and gates (Figures 5 and 6). 383
384 Figure 8. Distribution of mean indicators of significance of encroachment behaviours 385
with respect to distance from forest borders within fenced sites with grass strips and paths. 386 387 Fences did not significantly reduce waste disposal frequency or indicator relative to any 388
other boundary type (P > .05). In fact, fenced sites had significantly higher frequencies and 389
indicators than sites with grass strips, with and without paths, and higher frequencies of waste 390
disposal than sites with municipal boundary posts (P < .05). Notice the relatively high indicators 391
of waste disposal in fenced sites (Figure 5) relative to fenced sites with grass strips and paths 392
(Figure 8). 393
The heights of the fences may have been too low to discourage residents within their 394
yards from dumping over fences. The mean height of study site fences was 1.5 metres measured 395
from the municipal forest side of the fence. The height of the fence on the resident's side; 396
however, was often appreciably less than this since many residents installed raised flowerbeds, 397
patios and pool decks. These structures raised the grade of yards above that of the adjacent forest 398
edge, and effectively reduced the height of the fence on the side of the residence. While 399
increasing the height of the fence may result in reductions in waste disposal encroachment; there 400
was no correlation between fence heights (ranging from 91 to 163 cm) and waste disposal mean 401
frequency and indicator of intensity (P>.05). 402
403 4.3.3 Forest recreation encroachment 404 405
Fenced sites reduced the mean frequency and indicator of forest recreation-related 406
encroachment relative to that occurring in fenced sites with gates (Figures 5 and 6), and fenced 407
sites with grass strips and paths (Figure 8) (P < .05). For example, all fenced sites with gates had 408
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unauthorized pathways leading from residential yards into the forest edge, while few fenced sites 409
had these pathways. The grass strip appeared to increase access to the forest border for this type 410
of encroachment, and many pathways were used for waste disposal, sometimes in addition to 411
forest recreation. Closed side canopies did not appear to discourage unauthorized pathway 412
creation. Unauthorized pathways were observed throughout many of the study sites, particularly 413
within forests with a sparsely growing understory. 414
415 4.3.4 Residential encroachment in response to forest encroachment 416 417
None of the boundary treatments eliminated residential encroachment in response to 418
forest encroachment. Although the frequency and indicator of encroachment in response to 419
forest encroachment within residential yards was higher in fenced sites than in sites with grass 420
strips, the difference was not significant (P > .05). A grass strip may separate the residential 421
property from the forest border, thereby removing the encroaching forest vegetation from the 422
property boundary; however, further proof is required to support this theory. 423
424 4.3.5 Garden plant invasions 425 426
None of the boundary treatments eliminated garden plant invasions, although grass strips 427
significantly reduced their occurrence relative to sites without grass strips. Sites with grass strips 428
had a significantly lower mean frequency and mean indicator of garden plant invasion than sites 429
without grass strips (P <.05). Grass strips and paths may serve as a barrier to the dispersal of 430
garden plants that spread through vegetative reproduction. 431
Fences were ineffective as barriers to this type of encroachment. Garden plant invasions 432
were just as frequent and covered just as much area in fenced sites as sites without fences (P 433
>.05). Boundaries with high frequencies and indicators of waste disposal encroachment may also 434
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increase garden plant invasions that enter forest edges through the disposal of viable plant 435
propagules in waste. Similarly, boundaries that abut residential yards with forest borders (e.g. 436
fenced sites) may also encourage garden plant invasions planted by residents. Informal 437
conversations with residents during sampling indicated some residents planted forest edges to 438
improve the aesthetic appearance of the forest edge. 439
440 5.0 Discussion 441 442 Boundary-focused passive management measures can significantly limit the area of 443
encroachment within forest edges. For example, those containing components that reduce 444
resident access to forest edges (e.g. fences, grass strips with and without pathways) led to 445
significantly lower areas of encroachment than those with no restrictions, or that encouraged 446
access to forest borders (e.g. no boundary demarcation, or fences with gates). Fences (with no 447
gates) appeared to concentrate the frequency and area cover of encroachment closer to forest 448
borders. This finding is supported by a study that found fences significantly reduce the maximum 449
extent of encroachment within forest edges (McWilliam et al., 2010). Other recreation ecology 450
studies have demonstrated similar relationships between human activity impacts and access 451
(Matlack, 1993; Roggenbuck and Lucas, 1987; Loeb, 1989; Furuseth and Altman, 1991). 452
Reducing access to urban natural systems, or to those sensitive to human activity impacts, may 453
reduce some social and economic values of urban natural systems, such as recreational 454
opportunities or real estate values, and residential areas and urban natural systems are commonly 455
planned to maximize the exposure of natural systems to residential land uses in order to 456
maximize these latter values. However in doing so, ecological services and some recreation-457
related values may be compromised. Furthermore, forest management resources required to 458
protect these latter values may have to be increased if these values are to be maintained for the 459
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long term. Key ecological, social and economic functions of natural systems need to be clearly 460
identified and communicated to surrounding communities so that planning and management 461
decisions can be made in support of these functions prior to and following adjacent land use 462
development. 463
Different boundary components were effective in reducing the area cover of different 464
encroachment behaviours with no one boundary component effective in reducing all behaviours. 465
Therefore, to maximize the effectiveness of boundary-focused passive management measures, 466
multiple boundary components need to be designed into a boundary treatment. Boundary 467
treatments should include fences (without gates) to reduce the incidence of yard extension 468
encroachment both within forest edges and adjacent mown grass strips, and to concentrate 469
encroachment as close to the forest border as possible. Although differences between boundary 470
treatments for reducing the extent of encroachment were not statistically significant within this 471
study, the evidence from this and other studies (example, McWilliam et al., 2010; Matlack, 472
1993) suggest that fences and other structures that effectively limit access to forest borders 473
significantly reduce the extent of encroachment activities. Fences significantly reduced 474
encroachment whether residents installed them on their own land, or the municipality installed 475
them on municipal land. However, if the fence is installed on municipal land, the municipality 476
has the right to remove resident-installed gates from fences. They do not have this right if the 477
fence is installed on resident-owned land. Furthermore, if the fence is installed on resident land, 478
the resident may remove the fence. A survey of boundary treatments within the pilot study 479
indicated that in absence of municipal fences, residents preferred no boundary treatment, or 480
installed fences with gates. Under these boundary treatments, the results indicate encroachments 481
will significantly increase. A few residents did install gates within municipal fences. This led to 482
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higher levels of encroachment within forest edges, particularly yard extensions (Figure 9). 483
Therefore, to minimize encroachment within forest edges, municipalities should ensure fences 484
are installed on municipal land, gates are not authorized, and fences are periodically monitored to 485
ensure the removal of gates. 486
Figure 9 Some residents place illegal gates (indicated by arrow) in municipal fences 487 leading to a significant increase in the area of encroachment. 488 (Photo: Village Wood Park, Oakville. Source: McWilliam, 2005) 489
490
Other boundary components (or other measures) are needed to complement fences, to 491
reduce waste disposal encroachment, yard plant invasions, and encroachments related to resident 492
responses to forest encroachment. Relative to fences, grass strips were effective in reducing, 493
waste disposal, yard plant invasions and encroachment in reaction to forest encroachment. 494
However, grass strips need to be coupled with fences to achieve these results. For example, 495
without fences, mown grass strips tend to encourage yard extensions within mown grass strips 496
meant to provide other functions, such as public recreation facilities, stormwater management or 497
utility corridor maintenance. 498
Despite the benefits of mown grass strips for reducing these forms of encroachment, they 499
do not provide supplemental wildlife habitat to urban forests, their maintenance generates air and 500
noise pollution, and absorbs municipal management budgets that could otherwise be used in 501
monitoring or education programs to further protect forests from encroachment. 502
Many remaining forest fragments within Southern Ontario tend to be too small in area 503
and convoluted in shape to provide habitat to sensitive, less common species requiring larger 504
areas or separation from human disturbance. Many also have a high edge to interior ratio that 505
leaves them highly exposed to adjacent land use impacts. Official or Secondary plan policies 506
within Southern Ontario municipalities often require forested buffers with development adjacent 507
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to some natural area designations in order to improve their wildlife values and resistance to 508
construction impacts (McWilliam, 2009). While forested buffers could segregate encroachment 509
activities from occurring within designated forest areas, they do not limit encroachment that lead 510
to the loss or degradation of forested habitat within buffers. It is possible that mown grass strips 511
do not have to be wide to limit encroachment, and therefore, only a small portion of the forested 512
buffer would have to be dedicated to encroachment protection. However further research is 513
required to determine the minimum effective width of mown grass strips for limiting these 514
encroachment behaviours. 515
The addition of pathways could further improve the performance of mown grass strips for 516
limiting encroachment by encourage municipal and informal community monitoring of 517
boundaries, and by clearly delineating municipal from resident-owned property. Furthermore, 518
they direct recreation-related impacts on forests away from the more sensitive interior forest 519
area, in addition to facilitating municipal edge management activities, such as hazardous tree and 520
encroachment removal. However, there was an insufficient number of sites with pathways 521
existing within study municipalities to determine the efficacy of pathways, independent of grass 522
strips, for limiting encroachment. 523
The results of this study have contributed to a better understanding of the relationship 524
between boundary treatment and the area of forest edge behind residential properties that can be 525
affected by encroachment. Landscape architects and planners can use the results to design and 526
implement residential developments that will have the advantages of living near natural areas, 527
but will also protect the integrity of those natural areas. 528
529 Acknowledgements 530 531
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