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Trends in land cover change and isolation of protected areas at the interface of the southern boreal mixedwood and aspen parkland in Alberta, Canada
Forest Ecology and Management 230 (2006) 151–161 www.elsevier.com/locate/foreco
Trends in land cover change and isolation of protected areas at the interface of the southern boreal mixedwood and aspen parkland in Alberta, Canada Jason E. Young a, G. Arturo Sa´nchez-Azofeifa a,*, Susan J. Hannon b, Ross Chapman c a
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alta. T6G 2E3, Canada b Department of Biological Sciences, University of Alberta, Edmonton, Alta. T6G 2E9, Canada c Elk Island National Park, RR # 1 Site 4 Fort Saskatchewan, Alta. T8L 2N7, Canada Received 28 January 2005; received in revised form 19 April 2006; accepted 20 April 2006
Abstract The Beaver Hills region of central Alberta is located at the interface of the southern boreal mixedwood forest and the aspen parkland, an area now dominated by agriculture, urban and industrial development. Increasing anthropogenic land cover will eventually isolate remaining natural habitats currently protected in parks and reserves. This paper analyzes land cover and land cover change (LCC) in the Beaver Hills moraine and surrounding areas using a structured hierarchical satellite imagery classification applied to Landsat Multi Spectral Scanner and Thematic Mapper from 1977, 1987, and 1998. Our goal was to quantify deforestation and habitat fragmentation trends and then discuss how this information could be used to develop a conservation approach that will protect current areas against further habitat loss. We found that the rate of deforestation in the lands surrounding the moraine was similar to the broad trend at the southern periphery of the Canadian boreal forest region: annual rate of change in forest cover was 0.82%/year. However, in the Beaver Hills there was a net gain of +0.61%/year, due to regeneration of low quality agricultural lands. All fragmentation indices used indicated an increase in forest fragmentation. We designed a network of protected areas and remaining large forest patches, based on the UNESCO-MAB biosphere model. Our results underline concerns regarding the increasing isolation of national parks and biological reserves in Canada. # 2006 Elsevier B.V. All rights reserved. Keywords: Aspen parkland; Land cover change; Isolation of national parks; Conservation and management
1. Introduction Traditionally, land use and land cover change (LUCC) research in boreal and parkland regions focused on natural processes, such as succession and natural disturbances rather than the causes and consequences of deforestation (Bonan and Shugart, 1989; Geist and Lambin, 2002). In some areas of the boreal/parkland interface, rates of deforestation have exceeded three times the world average (Alberta Environmental Protection, 1998; Hobson et al., 2002). Four main forces drive changing regional land cover in this region: agriculture, urbanization, oil and gas activities and changes in fire regime. Concomitant with land use change is the increasing isolation of national parks and biological reserves. Although, a significant
* Corresponding author. Tel.: +1 780 492 1822; fax: +1 780 492 2030. E-mail address: [email protected] (G.A. Sa´nchez-Azofeifa). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.04.031
amount of literature exists regarding the isolation of natural protected areas, this information is biased towards tropical environments (Sa´nchez-Azofeifa et al., 1999, 2002, 2003a; Bruner et al., 2001; Schmiegelow and Mo¨nnkko¨nen, 2002; Hobson et al., 2002; DeFries et al., 2005). In the context of the interface of the southern boreal mixedwood and aspen parkland of Alberta, little is known about the dynamics of land cover change (LCC) and how these dynamics contribute to habitat loss and fragmentation. Early settlers were employed in the fur trade out of Fort Edmonton (site of present-day Edmonton), but the population began to expand rapidly after the 1870’s, when land was offered to settlers for agriculture. A combination of land clearing, elimination of wildfire, and decreased wild herbivore pressure has changed the vegetation from a mix of aspen, shrub, grassland, and spruce to a matrix of agricultural lands (pasture and crop) with small stands of aspen (Gunning, 2001). Currently, land is protected in one national park (Elk Island
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National Park) and in a few smaller reserves with little connectivity between them. The objective of this paper is to quantify the changes in land cover in the Beaver Hills region (Alberta, Canada) that have occurred over the last two decades, and to describe and discuss a potential protected areas network for the region. The area represents one the largest blocks of aspen dominated lower boreal mixedwood forest currently remaining in the Alberta landscape, a type of landscape that is becoming extremely rare. Furthermore, we discuss the nature of the forces contributing to land cover change and habitat loss and describe the continued isolation of the only protected areas currently present in this interface between the southern boreal mixedwood and aspen parkland of Alberta.
2. Methods 2.1. Study area The study area was defined as all lands within 50 km of Elk Island National Park (EINP). This area includes the Beaver Hills (The Beaver Hills Moraine, also known as the Cooking Lake Moraine), the City of Edmonton, and Strathcona County in east-central Alberta, Canada (Fig. 1). The Beaver Hills occupy approximately, 800 km2 on the eastern limits of the City of Edmonton. In order to provide greater perspective on the spatial variability of land cover changes, the study area was analyzed both as a whole and in two sub-sets consisting of the Beaver Hills and all lands
Fig. 1. Location of the study area in Alberta, Canada.
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outside of the Beaver Hills. These regions are hereafter referred to as ‘study area’, ‘Beaver Hills’, and ‘surrounding lands’, respectively. Located in the Southern Boreal Plains and Plateau Natural Region, the study area is in a transitional area of the southern boreal mixedwood forest dominated by Trembling aspen (Populus tremuloides). Other less dominant native trees include Balsam poplar (Populus balsamifera), White spruce (Picea glauca), Black spruce (Picea mariana), and White birch (Betula papyrifera). The understory is in part comprised of Red osier dogwood (Cornus stolonifera), Beaked hazelnut (Corylus cornuta), and Saskatoon Berry (Amelanchier alnifolia). Rising a few meters above the surrounding plains, this hummocky knob and kettle terrain has a variety of wetlands scattered throughout. Elk Island National Park represents one of Canada’s 39 natural regions and has a wealth of unique biodiversity: over 40 native mammals, 200 species of birds, and 600 plants are found in Elk Island and in the Beaver Hills area (Parks Canada, 2004). Preserving a remnant herd of native elk was the driving force behind setting aside the park in 1906. The park’s 194 km2 was carved out of the 442 km2 Cooking Lake Forest Reserve established in 1899 to prevent settlers from burning valuable timber (MacDonald, 1994). Realizing the valuable preservation and recreation significance of the Beaver Hills, two other protected areas, the Cooking Lake Blackfoot Multiuse Area and Ministik Bird Sanctuary were also created from the Cooking Lake Forest Reserve (Table 1 lists the protected areas within the study area). More recently, these protected areas have taken a more ecological approach to their management. Elk Island, for example, has moved away from an ungulate dominated management approach toward a more ecosystem approach that recognizes the significance of all native species and their biodiversity. Land cover changes in the Beaver Hills over the past several decades have been driven primarily by agricultural development: clearing land for crop and pasture for cattle. Economic development in Edmonton and Strathcona County and a population increase in the region of 8.9% between 1986 and 1996 have driven industrial and urban expansion (Graham and McFarlane, 2001). The Beaver Hills region contains a number of protected areas, including Elk Island National Park, Ministik Bird
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Sanctuary, Cooking Lake/Blackfoot multi-use (recreation) area, and the Miquelon Lake protected area (Table 1). Elk Island National Park currently holds populations of six species that are designated as endangered, threatened or of special concern some of which are data deficient including: wood bison (Bison b. athabascae), Trumpeter swan (Cygnus buccinator), Loggerhead shrike (Lanius ludovicianus excubitorides), Blackthroated green warbler (Dendroica virens), Western toad (Bufo boreas), and Canadian toad (Bufo hemiophrys). These species have been assessed federally by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and provincially by the Alberta Endangered Species Conservation Committee (AESCC). 2.2. Satellite imagery and image preprocessing Land cover change and landscape fragmentation dynamics for all lands within 50 km of Elk Island National Park (EINP) were examined, including the city of Edmonton, Alberta. A 50 km buffer from the boundary of EINP was chosen in order to include enough of the private lands surrounding the Beaver Hills to make comparisons with regional deforestation/fragmentation trends. At the same time, this buffer was small enough to allow field data collection for the calibration and validation of the remote sensing component of this paper. Ground cover characterization and ground cover change maps were derived from the interpretation of Landsat Multi-Spectral Scanner (MSS—80 m resolution and 4 spectral bands) and Thematic Mapper (TM—28.5 m resolution and 7 spectral bands) satellite image data captured two decades apart from 1977 to 1998. The images were selected to provide the maximum temporal spread possible. Earlier Landsat images were available (1973), but a very high amount of horizontal banding in the images made them unsuitable for classification. Because the study area falls on the border between two scenes (TM path 42, rows 22 and 23), pairs of consecutive images were used from 1977 and 1998. There were no available pairs of cloud free scenes for the mid-late 80’s, so a pair was constructed using one 1986 image and one 1988 image (hereafter referred to as the 1987 scene). Cloud free images were unavailable between 1998 and 2001 when the ground truth data was collected. Summer images were used (when all deciduous trees have their leaves on,
Table 1 Status of different conservation area surrounding the Elk Island National Park Protected area
Habitat type protected
Level of protection
Elk Island National Park (194 km2) Ministik Bird Sanctuary (109 km2) Beaver Hill Lake (land: 70 km2 water: 125 km2) Cooking Lake Blackfoot Multiuse Area (100 km2) Miquelon Lake Protected Area (36 km2)
A (highest level of ecological protection)
Emphasis of ecosystem preservation for all native species as well as restoration and monitoring Individual species approach, emphasis on bird preservation
B B C D (lowest level of ecological protection)
Individual species approach, emphasis on bird preservation, little shore line protection from agriculture Multi-user approach with marginal concern with habitat restoration (hunting, dog sledding, hiking, grazing, oil and gas wells) Multi-user approach including land development, acreage subdivisions
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Table 2 Details on the satellite images used in this study Date (dd/mm/yyyy) 18/06/1977 18/06/1977 26/05/1986 19/08/1988 11/05/1998 16/08/1998 a
Sensor (Landsat) MSS MSS TM TM TM TM
Path/row a
45 /22 45a/23 42/22 42/23 42/22 42/23
RMS error (m)
Resolution (re-sampled) (m)
45 51 37 40 18 18
75 75 25 25 25 25
Equivalent to TM path 42.
June–September) to reduce sun-angle and phenological differences. Image details and dates are given in Table 2. All images were registered to a Universal Transverse Mercator (UTM) projection system: zone 12 north, spheroid GRS 1980, datum NAD 83. The 1977 images were resampled to a pixel size of 75 m (from 80 m) and all other images were re-sampled to 25 m. Orthorectification was not necessary due to the relatively low relief in the area. Atmospheric correction of the images was also not necessary because each image was classified independently (Song et al., 2001). The study area is smaller than a full Landsat scene, so after registration the images were trimmed to cover only the area of interest. Archived air photos were purchased to assess the classification accuracy of the 1977 and 1987 images. These photos were registered to 1:20,000 Alberta provincial vector data. To provide a visual verification, the photos were chosen in areas where significant land cover change was identified in satellite images. The time lag between the 1998 imagery and the ground truth collection was not considered to be significant enough to warrant the cost of purchasing aerial photographs for 1998. 2.3. Image classification The classification of the satellite images was based on the Alberta Ground Cover Characterization (AGCC) hierarchical method (Sa´nchez-Azofeifa et al., 2003b). This technique involves sequential separation of the feature pixels in the image into groups based on spectral characteristics. Spectral clusters were obtained by unsupervised classification using the algorithm Iterative Self-Organizing Data Analysis Technique (ISODATA). This method is a variation of the K-mean method in which clusters are formed with minimum spectral distance, and then cluster means are adjusted iteratively. Field data for the classification and verification of the land cover maps were obtained in two field trips during the late spring and early fall of 2001 (May and September). We recorded geographical coordinates, a description of the dominant vegetation and took photos of the site. Sites were chosen that were located at least 50 m from the edge of patches, in relatively homogeneous areas of at least one ha. In total, 1027 data points were recorded. The database of land cover points was randomly divided into two sets, creating one set for image calibration (529 points), and one set for verification/error
analysis of the classification (421 points). Classes extracted were: water, urban, crops/agriculture, range (natural and anthropogenic grasslands), and deciduous forest. From the 1977 and 1987 aerial photographs (the only years with available aerial photographs), we chose 236 random points for 1977 and 238 for 1987. A visual interpretation of land cover was recorded and compared with the land cover indicated by the classified image. To assess the accuracy of the classification of the 1998 imagery, the remaining field data points (those which were not used in the classification process) were compared with the classified image. A confusion matrix was generated and the accuracy statistics were estimates using the Kappa and Tau coefficients (Ma and Redmond, 1995). Kappa and Tau coefficients are known standard classification statistics used in land cover mapping. These two coefficients relate to the probability of having correctly classified a given pixel or polygon when compared with a random labeling. Of these two coefficients Tau is sometimes preferred over Kappa given its robustness (Ma and Redmond, 1995). Random checks for different classes (150 polygons in total) were conducted visually to verify whether a quantified land cover change was in fact ‘‘a change’’ and not an anomaly derived from inaccuracies in the different classifications used in this study. The annual rate of change of forest area (deforestation given in %/year) was calculated as r = (1/(t2 t1)) ln(A2/A1) where t = time and A = area (Puyravaud, 2003). Landscape metrics (class area, number of patches, mean and median patch size, standard deviation patch size, mean shape index, and Shannon’s diversity and evenness indices of all classes) were calculated for the entire study area, and for the Beaver Hills moraine only using Patch Analyst (Rempel, 2002). To determine the actual core area of each forest patch (i.e. the area not affected by edge-effects), we re-calculated the area of the patch by removing the area of forest within distances of 100 and 300 m from all edges or linear features. A review by Debinski and Holt (2000) found that edge effects could penetrate up to 300 m, but that species-specific avoidance distances can vary greatly (Jalkotzy et al., 1997). Mean patch core size, largest patch and the area greater than 300 ha were estimated for all core areas. To create the boundaries for the protected areas network all of the 1998 forest and wetland patches greater than 100 ha were selected as the largest, and therefore most significant, patches for conservation in the landscape. These patches were buffered at a distance of 500 m and 6 km.
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3. Results 3.1. Image classification and accuracy The overall accuracy for the land cover classification was estimated to be 95% for 1977, 91% for 1987, and 87% for 1998. Kappa and Tau statistics (Ma and Redmond, 1995) were 88% (e.g. the data was classified correct 88% of the time versus random assignment) for 1977, 80% and 82%, respectively for 1986/1988, and 82% for 1998. The accuracy of the change maps was estimated by the product of the accuracies of the original scenes, resulting in accuracy of 86% for 1977–1987, 79% for 1987–1998, and 83% for 1977–1998. These accuracies surpass Alberta’s provincial standards (75% overall accuracy) for mapping land use and land cover, using Landsat Thematic Mapper satellite information. Visual checks conducted using aerial photography between 1977 and 1987 on 150 selected 3 ha polygons detected as ‘‘change’’ during the land cover change analysis (1977–1987), indicated that these changes were actual changes on the ground in 95% of the cases. Observed problems occurred mostly in the
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wetland and water classes, an issue that is related to climatic conditions that tend to reduce or increase the problem around lakes. No such visual checks were possible between 1987 and 1998, given the lack of aerial photography during these years. 3.2. Land cover changes The percentage of the study area covered by croplands increased from 1977 to 1987 and remained stable at about 52% until 1998, whereas rangeland cover steadily decreased from 1977, occupying about 30% of the landscape by 1998 (Fig. 2a). The loss in rangeland appeared to be mainly due to conversion to croplands, with a net loss of about 60,000 ha in the first decade (Table 3). In the Beaver Hills subset of the study area more cropland was converted to rangeland than vice versa (Table 3). Wetlands and water were minor cover class components of the area (Fig. 2a). There was a net loss of wetlands in the first decade and a net gain in the second, whereas the reverse was true for water bodies (Table 3). Beaver Hills had a similar trend for water, but no change in wetland (Table 3).
Fig. 2. Land cover metrics for the Elk-Island region (50 km buffer area), southern Alberta, Canada. (a) Land cover proportion, (b) number of patches, (c) mean patch size distribution, (d) deviation in mean patch size, and (e) mean shape index.
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Table 3 Area (in hectares) for each land cover change class in the study area as a whole, and for the Beaverhills moraine separately Class
1977–88
1988–98
Study area No change Gain of urban Range to crop Crop to range Deforestation Afforestation Loss of wetland Gain of wetland Loss of water Gain of water
996709 4182 174163 114178 45671 23518 225 143 2274 4328
1977–88
1988–98
Beaver Hills 1111937 20621 90736 91515 15730 28063 149 334 4453 1852
252373 15 6416 7651 10098 7428 0 0 193 873
261851 338 3755 7202 2336 8841 0 0 460 263
Forest covered about 12% of the study area (Fig. 2a). There was a net loss of forest area (deforestation minus afforestation) between 1977 and 1987 (ca. 22,000 ha), followed by a gain in forest area from 1987 to 1998 (13,000 ha) in the study area (Table 3). A similar trend was observed for the Beaver Hills. Over the two decades, afforestation balanced deforestation in the study area, whereas much more land was afforested than deforested in the Beaver Hills. This increase in forest cover was associated with regeneration of lands initially utilized for croplands and range. Urban area also increased, mostly as result of the expansion of the City of Edmonton (Figs. 3 and 4; Table 3). Annual rates of deforestation, both in terms of deforestation, and in actual change in forest area (which accounts for afforestation), were higher from 1977 to 1987 than from 1987 to 1998 (Table 4). The rate of deforestation was higher in the entire study area than in the Beaver Hills. The largest single deforestation event was the clearing of the grazing leases in the Cooking Lake/Blackfoot area (within the Beaver Hills) between 1977 and 1987: 3036 ha were deforested, representing 30% of the 10,098 ha forest lost in the Beaver Hills. 3.3. Fragmentation metrics The number of patches increased over time in all land cover classes, with the largest increase occurring between 1987 and 1998 in the crop and range (Fig. 2b) category. There was a concomitant decrease in the mean patch size and the standard deviation in mean patch size over time for most cover classes (Fig. 2c and d). Values for shape index (higher values indicate more complex shape) peaked in 1987 (Fig. 2e). Shannon’s diversity index increased from 1.18 to 1.30 from 1977 to 1987 and then decreased to 1.27 in 1998, while evenness increased from 0.61 to 0.67 and then decreased to 0.65. Increase in Shannon’s evenness and diversity indices indicate an increase in both distribution and proportional distribution of land cover classes. The sharp decrease in mean patch size for the urban land cover class between 1977 and 1987 is the result of a change in resolution of the satellite imagery. The 1977 image does not resolve the small green spaces (parks and lawns) within the City
of Edmonton that are identifiable in the later imagery. This effect will not be significant outside of the city. The number of patches of forest steadily increased between 1977 and 1998 (Fig. 2b). Mean forest patch size decreased from 57 ha in 1977, 41 ha in 1987, to 30 ha in 1998. The 1998 forest landscape was very patchy, dominated by large tracts of crop and range. The core area of forest was calculated using buffers of 100 and 300 m from patch edges (Table 5). There was an overall decrease in core area between 1977 and 1987 (average decrease of 48%), with a rebound between 1987 and 1998 (average increase of 33%). Although, the largest patch and the area of patches greater than 300 ha were similar between 1977 and 1998, the largest patch of core forest and the area of core forest patches over 300 ha both declined over the two decades (Table 5). The results of buffering the 1998 forest and wetland patches of 100 ha and over at 0.5 and 6.0 km are shown in Fig. 5 as, respectively, the boundary for the buffer zone and the zone of cooperation. 4. Discussion and conclusion The Beaver Hills landscape has experienced a combination of land cover change processes: deforestation, fragmentation, and afforestation. The area of core forest patches greater than 300 ha has declined, with only 500 ha of core area (300 m buffer) remaining (Table 5), this is an 88% decrease since 1977. The increased fragmentation of the landscape (increased patch number, decreased patch size, higher shape index, increased diversity) correlates well with observed agricultural/economic trends for the County of Strathcona. Between 1981 and 1996, the number of crops and farms more than doubled the number of beef cows increased by 68%, and all other cattle increased by 38% (Toma and Bouma, 2003). Toma and Bouma (2003) concluded that there was an increase in small specialized agricultural operations and some extensive cattle operations, while the number of intensive livestock operations and traditional cropping operations declined, due in part to the high cost of land in the region. Afforestation in the Beaver Hills is in part a result of acreage and other landowners increasingly allowing their pastures to fill in with trees as well as the abandonment of marginal ranching/ farming operations and the subsequent natural conversion of the land back to forest. New forest is primarily composed of fast growing Trembling aspen (P. tremuloides), and to a lesser extent, Balsam Poplar (P. balsamifera) in wetter areas. The trees grow from the edges of pastures, often with underground rhizomes and/or from clumps within pastures that expand outward. In 2002, a 40 ha treed parcel adjacent to Elk Island National Park was logged. Within 3 years, the suckering Aspen poplars (P. tremuloides) are beginning once more to dominate the parcel through afforestation. Wetlands are largely fed by rainwater and so vary in size according to rainfall events. Some of the larger wetlands, such as shallow Tawayik Lake have shrunk by more than 10% over the course of the drought, which has lasted longer than the past 5 years.
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Fig. 3. Land cover for the Beaver Hill regions of Alberta: (a) 1977, (b) 1987, and (c) 1998. Cyan: Urban, Yellow: crops, Blue: water, Gold: range, Red: all forest types, Magenda: wetlands. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The situation in this study area is very similar to that presented by Hobson et al. (2002) for the southern edge of the boreal forest in Saskatchewan. In both cases, the majority of suitable lands have been converted to agriculture, there is a significant increase in afforestation as a result of land abandonment and a high rate of deforestation is observed as a result of cutting of forest patches. Similar patterns have been documented in Costa Rica (Van Laake and Sanchez-Azofeifa, 2004). The overall annual rate of deforestation in our region (accounting for secondary growth) is 0.27%, which is less than the 0.89% reported in Saskatchewan and very close to the 0.24% world average for all forests (FAO, 2001; Hobson et al., 2002). This figure masks a great deal of spatial and temporal
variation, however, with rates ranging from 2.38% deforestation in the lands surrounding the Beaver Hills between 1977 and 1987, to 2.00% afforestation in the Beaver Hills between 1987 and 1998. Examining regional trends also masks significant local events. The Blackfoot grazing leases were cut between 1980 and 1984 into the largest contiguous patch of forest that existed in the study area. The clearing resulted in an immediate and significant loss of core forest area and concomitant increase in fragmentation, both in terms of land cover and the associated roads and fences required for the grazing leases. In addition to the immediate impact of the clearing itself, grazing cattle can have significant impacts on vegetation (including damage to native species and
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Fig. 4. Land cover change Beaver Hill region. Red represents deforestation, green afforestation and Cyan increase in urbanization. (a) Land cover change 1977–1987, (b) Land cover change 1987–1998 and (c) Land cover change 1977–1998. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Table 4 Rate (%/year) of deforestation and change in total forest area (accounting for deforestation and afforestation) Time period
Study area Deforestation only
1977–1987 1987–1998
2.54 1.07
Beaver Hills Total change in forest area 1.74 1.35
Deforestation only 1.53 0.39
Total change in forest area 0.65 2.00
J.E. Young et al. / Forest Ecology and Management 230 (2006) 151–161 Table 5 Area of forest and core forest habitat, mean patch size, area of largest patch and area of all forest patches larger than 300 ha in the complete study area surrounding the Elk Island National Park, Alberta, Canada 1977
1987
1998
No buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area >300 (ha)
187000 57 35000 116000
155000 41 13000 90000
177000 30 36000 113000
100 m buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area >300 (ha)
67000 17 2000 15000
42000 14 1600 5000
50000 16 1600 8000
300 m buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area > 300 (ha)
11000 33 1100 4000
4600 21 500 500
6700 22 500 500
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invasion of exotic plants), bird and mammalian communities (due to habitat reduction or structural changes, spread of disease, and fencing), and water quality (due to damaged riparian vegetation and fecal contamination) (Coker and Capen, 1995; Donald et al., 1998; Jenkins and Parker, 2000). Networks of protected areas representing a diversity of communities are the best way to maintain biodiversity (Primack, 2002). Theories of island biogeography suggest that the size, shape, and connectivity of a reserve will impact its success at conserving ecological integrity (MacArthur and Wilson, 1967; Primack, 2002). The size of a park is the most critical factor in its ability to conserve biodiversity. The minimum reserve area required to conserve species diversity in parks in North American is on the order of 10,000 km2 (Newmark, 1995; Gurd et al., 2001; Wiersma, 2001), a reality that it is impossible to achieve in our study area. To overcome this problem, it may be possible to increase the effective area by using corridors and buffer zones that connect small-protected areas into a larger network (Gurd et al., 2001). The mean size of protected areas in the study area is 930 ha, much smaller that the 10,000 km2 minimum recommended size. If all of these protected areas were to become isolated, then the chances for maintaining the current diversity of species in the Beaver Hills would be slim.
Fig. 5. Example of a possible protected area network. Zones include the core areas (currently protected), the buffer zone (high conservation priority), and the zone of cooperation (sustainable development). Lighter gray areas of the image indicate cropland. Letter between parentheses refer to different levels of protection as per Table 1.
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A protected area network could be created in the study area, based on the UNESCO biosphere model (Fig. 5) (UNESCO, 1995). The network is composed of three zones: a core of strict habitat protection, a buffer of compatible use, and a zone of cooperation in which sustainable development is permitted within limitations based on compatibility with the conservation requirements. The five largest currently protected areas in the study area (Elk Island, Beaver Hill Lake, Cooking LakeBlackfoot, Ministik Lake, Miquelon Lake) are already clustered together due to their creation from the initial forest reserve and could form the core conservation area. A first estimation of the boundaries for the buffer zone and zone of cooperation was established based on buffers around the largest patches of forest and wetland, but the actual zone boundaries would depend on variables including location of rare or endangered species and the degree of cooperation from local stakeholders. Rehabilitation of at least one of the central grazing plots in the Blackfoot multi-use area at the Cooking Lake/Blackfoot region (Fig. 5) would improve connectivity between the remaining core areas. A buffer zone around Elk Island and the other protected areas must be assessed as well. The significance of the terrestrial and wetland habitats in the Beaver Hills provide justification for application for joint protection under the UNESCO Man and the Biosphere (MAB) program and the RAMSAR Convention on Wetlands (MAB, 2002). To be successful, the proposed UNESCO biosphere model must address the fact that the creation of additional national parks in this fragmented ecosystem is not realistic and that Elk Island National Park has become systematically more isolated from the forest matrix. Instead, the development of biological corridors and the promotion of private reserves, under a scheme for payments for environmental services (PES), is a more realistic option for conservation. Experiences, such as those developed by the Costa Rica National Financing Fund (FONAFIFO) aimed to promote conservation under PES must be studied before they are implemented in the boreal forest/ aspen parkland. Efforts by organizations, such as the Nature Conservancy of Canada that already operate in the Beaver Hills acquiring land covenants for conservation must be expanded as well. Acknowledgements We would like to thank Elk Island National Park for data and logistical support. The Canada Foundation for Innovation (CFI) and the National Network of Centers of Excellence: Sustainable Forest Management Network (NCE-SFMN) also provided support for this research initiative. References Alberta Environmental Protection, 1998. The Boreal forest natural region of Alberta. Unpublished report for the Special Places 2000 Provincial Coordinating Committee. Bonan, G.B., Shugart, H.H., 1989. Environmental factors and ecological processes in boreal forests. Anual Rev. Ecol. Syst. 20, 1–28.
Bruner, A.G.G., Raymond, E., Richard, E., da Fonseca, G.A.B., 2001. Effectiveness of parks in protecting tropical biodiversity. Science 291, 125–129. Coker, D.R., Capen, D.E., 1995. Landscape-level habitat use by Brown-Headed Cowbirds in Vermont. J. Wildl. Manag. 59 (4), 631–637. Debinski, D.M., Holt, R.D., 2000. A survey and overview of habitat fragmentation experiments. Conserv. Biol. 14 (2), 342–355. DeFries, R., Hansen, A., Newton, A.C., Hansen, M.C., 2005. Increasing isolation of protected areas in tropical forests over the last 20 years. Ecol. Appl. 15 (1), 19–26. Donald, P.F., Fuller, R.J., Evans, A.D., Gough, S.J., 1998. Effects of forest management and grazing on breeding bird communities in plantations of broadleaved and coniferous trees in western England. Biol. Conserv. 85, 183–197. FAO, 2001. The State of the World’s Forests. FAO, Rome. Geist, H.J., Lambin, E.F., 2002. Proximate causes and underlying driving forces of tropical deforestation. BioScience 52 (2), 143–150. Graham, J., McFarlane, B.L., 2001. Demographic Characteristics of Selected Communities in or Near the Cooking Lake Moraine. Nature Conservancy of Canada, Alberta Region, Parks Canada Agency, Strathcona County, Edmonton, Alberta, Canada. Gunning, M.J., 2001. A century of vegetation changes in western Canada’s boreal forest—grassland ecotone derived from soil charcoal analysis. M.Sc. thesis. University of Alberta, Edmonton, AB, Canada. Gurd, D.B., Nudds, T.D., Rivard, D.H., 2001. Conservation of mammals in eastern North American wildlife reserves: how small is too small? Conserv. Biol. 15, 1355–1363. Hobson, K.A., Bayne, E.M., Van Wilgenburg, S.L., 2002. Large-scale conversion of forest to agriculture in the boreal plains of Saskatchewan. Conserv. Biol. 16, 1530–1541. Jalkotzy, M.G., Ross, P.I., Nasserden, M.D., 1997. The effects of linear developments on wildlife: a review of selected scientific literature. Arc Wildlife Services Ltd., Calgary, AB, 142 pp. Jenkins, M.A., Parker, G.R., 2000. Changes in the forest landscape of the Charles C. Deam Wilderness, Southern Indiana, 1939–1990. Nat. Areas J. 20 (1), 46–55. MAB, 2002. Conclusions of the EuroMAB workshop on ‘‘the role of wetlands in biosphere reserves’’. Man and the Biosphere (MAB) secretariat. Available at http://www.unesco.org/mab/cooperation/Ramsar/Czmeet2002.doc (accessed March, 2003). Ma, Z., Redmond, R., 1995. Tau coefficients for accuracy assessment of classification of remote sensing data. Photo. Eng. Remote Sensing 61, 435–439. MacArthur, R.H., Wilson, E.O., 1967. The Theory of Island Biogeography. Princeton University Press, Princeton, N.J. MacDonald, G., 1994. Science and History at Elk Island: Conservation Work at a Canadian National Park 1906-1994, Parks Canada document, p. 73. Newmark, W.D., 1995. Extinction of mammal populations in western North American national parks. Conserv. Biol. 9 (3), 512–526. Parks Canada Report, 2004. Elk Island National Park Ecosystem Conservation Plan, p. 15. Primack, R.B., 2002. Essentials of Conservation Biology, third ed. Sinauer Associates Inc., Sunderland, MA, USA. Puyravaud, J.P., 2003. Standardizing the calculation of the annual rate of deforestation. Forest Ecol. Manag. 177 (1–3), 593–596. Rempel, R., 2002. Patch Analyst 2.2 (build 34). Available from http://flash. lakeheadu.ca/rrempel/patch/download.html (accessed 9 April, 2003). Sa´nchez-Azofeifa, G.A., Quesada-Mateo, C., Gonzalez-Quesada, P., Dayanandan, S., Bawa, K.S., 1999. Protected areas and conservation of biodiversity in the tropics. Conserv. Biol. 13 (2), 407–411. Sa´nchez-Azofeifa, G.A., Rivard, B., Calvo, J., Moorthy, I., 2002. Dynamics of tropical deforestation around national parks: remote sensing of forest change on the Osa Peninsula of Costa Rica. Mt. Res. Dev. 22 (4), 352– 358. Sa´nchez-Azofeifa, G.A., Daily, G.C., Pfaff, A.S.P., Busch, C., 2003a. Integrity and isolation of Costa Rica’s national parks and biological reserves: examining the dynamics of land-cover change. Biol. Conserv. 109, 123– 135.
J.E. Young et al. / Forest Ecology and Management 230 (2006) 151–161 Sa´nchez-Azofeifa, G.A., Kachmar, M., Kalacska, M., Hamilton, S., 2003b. Experiences in field data collection in support of land use and land cover change classification in boreal and tropical environments. In: Remote Sensing of Forest Environments: Concepts and Case Studies, Kluwer Academic Publishers, pp. 433–446. Schmiegelow, F.K.A., Mo¨nnkko¨nen, M., 2002. Habitat loss and fragmentation in dynamic landscapes: avian perspectives from the boreal forest. Ecol. Appl. 12 (2), 375–389. Song, C., Woodcock, C.E., Seto, K.C., Lenney, M.P., Macomber, S.A., 2001. Classification and change detection using Landsat TM data: when and how to correct atmospheric effects? Remote Sensing Environ. 75 (2), 230–244.
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Toma and Bouma/Stantec Consulting, 2003. The future of agriculture. Sherwood Park, Alberta, Canada. Available at http://www.strathcona.ab. ca/Strathcona/Departments/Corporate+Planning+Secretariat/Future+of+ Agriculture+Report.htm (accessed March, 2003). UN ESCO, 1995. The Seville strategy for biosphere reserves. Man and the Biosphere (MAB) secretariat. Available at http://www.unesco.org/mab/ docs/strategy.doc (accessed March, 2003). Van Laake, P., Sanchez-Azofeifa, G.A., 2004. Focus on deforestation. Agric. Ecosys. Environ. 102 (1), 3–15. Wiersma, Y.F., 2001. When is a small park big enough? Effects of size, isolation and human disturbance on mammal species relaxation in Canadian national parks. M.Sc. thesis. University of Guelph.
Trends in land cover change and isolation of protected areas at the interface of the southern boreal mixedwood and aspen parkland in Alberta, Canada Jason E. Young a, G. Arturo Sa´nchez-Azofeifa a,*, Susan J. Hannon b, Ross Chapman c a
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alta. T6G 2E3, Canada b Department of Biological Sciences, University of Alberta, Edmonton, Alta. T6G 2E9, Canada c Elk Island National Park, RR # 1 Site 4 Fort Saskatchewan, Alta. T8L 2N7, Canada Received 28 January 2005; received in revised form 19 April 2006; accepted 20 April 2006
Abstract The Beaver Hills region of central Alberta is located at the interface of the southern boreal mixedwood forest and the aspen parkland, an area now dominated by agriculture, urban and industrial development. Increasing anthropogenic land cover will eventually isolate remaining natural habitats currently protected in parks and reserves. This paper analyzes land cover and land cover change (LCC) in the Beaver Hills moraine and surrounding areas using a structured hierarchical satellite imagery classification applied to Landsat Multi Spectral Scanner and Thematic Mapper from 1977, 1987, and 1998. Our goal was to quantify deforestation and habitat fragmentation trends and then discuss how this information could be used to develop a conservation approach that will protect current areas against further habitat loss. We found that the rate of deforestation in the lands surrounding the moraine was similar to the broad trend at the southern periphery of the Canadian boreal forest region: annual rate of change in forest cover was 0.82%/year. However, in the Beaver Hills there was a net gain of +0.61%/year, due to regeneration of low quality agricultural lands. All fragmentation indices used indicated an increase in forest fragmentation. We designed a network of protected areas and remaining large forest patches, based on the UNESCO-MAB biosphere model. Our results underline concerns regarding the increasing isolation of national parks and biological reserves in Canada. # 2006 Elsevier B.V. All rights reserved. Keywords: Aspen parkland; Land cover change; Isolation of national parks; Conservation and management
1. Introduction Traditionally, land use and land cover change (LUCC) research in boreal and parkland regions focused on natural processes, such as succession and natural disturbances rather than the causes and consequences of deforestation (Bonan and Shugart, 1989; Geist and Lambin, 2002). In some areas of the boreal/parkland interface, rates of deforestation have exceeded three times the world average (Alberta Environmental Protection, 1998; Hobson et al., 2002). Four main forces drive changing regional land cover in this region: agriculture, urbanization, oil and gas activities and changes in fire regime. Concomitant with land use change is the increasing isolation of national parks and biological reserves. Although, a significant
* Corresponding author. Tel.: +1 780 492 1822; fax: +1 780 492 2030. E-mail address: [email protected] (G.A. Sa´nchez-Azofeifa). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.04.031
amount of literature exists regarding the isolation of natural protected areas, this information is biased towards tropical environments (Sa´nchez-Azofeifa et al., 1999, 2002, 2003a; Bruner et al., 2001; Schmiegelow and Mo¨nnkko¨nen, 2002; Hobson et al., 2002; DeFries et al., 2005). In the context of the interface of the southern boreal mixedwood and aspen parkland of Alberta, little is known about the dynamics of land cover change (LCC) and how these dynamics contribute to habitat loss and fragmentation. Early settlers were employed in the fur trade out of Fort Edmonton (site of present-day Edmonton), but the population began to expand rapidly after the 1870’s, when land was offered to settlers for agriculture. A combination of land clearing, elimination of wildfire, and decreased wild herbivore pressure has changed the vegetation from a mix of aspen, shrub, grassland, and spruce to a matrix of agricultural lands (pasture and crop) with small stands of aspen (Gunning, 2001). Currently, land is protected in one national park (Elk Island
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National Park) and in a few smaller reserves with little connectivity between them. The objective of this paper is to quantify the changes in land cover in the Beaver Hills region (Alberta, Canada) that have occurred over the last two decades, and to describe and discuss a potential protected areas network for the region. The area represents one the largest blocks of aspen dominated lower boreal mixedwood forest currently remaining in the Alberta landscape, a type of landscape that is becoming extremely rare. Furthermore, we discuss the nature of the forces contributing to land cover change and habitat loss and describe the continued isolation of the only protected areas currently present in this interface between the southern boreal mixedwood and aspen parkland of Alberta.
2. Methods 2.1. Study area The study area was defined as all lands within 50 km of Elk Island National Park (EINP). This area includes the Beaver Hills (The Beaver Hills Moraine, also known as the Cooking Lake Moraine), the City of Edmonton, and Strathcona County in east-central Alberta, Canada (Fig. 1). The Beaver Hills occupy approximately, 800 km2 on the eastern limits of the City of Edmonton. In order to provide greater perspective on the spatial variability of land cover changes, the study area was analyzed both as a whole and in two sub-sets consisting of the Beaver Hills and all lands
Fig. 1. Location of the study area in Alberta, Canada.
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outside of the Beaver Hills. These regions are hereafter referred to as ‘study area’, ‘Beaver Hills’, and ‘surrounding lands’, respectively. Located in the Southern Boreal Plains and Plateau Natural Region, the study area is in a transitional area of the southern boreal mixedwood forest dominated by Trembling aspen (Populus tremuloides). Other less dominant native trees include Balsam poplar (Populus balsamifera), White spruce (Picea glauca), Black spruce (Picea mariana), and White birch (Betula papyrifera). The understory is in part comprised of Red osier dogwood (Cornus stolonifera), Beaked hazelnut (Corylus cornuta), and Saskatoon Berry (Amelanchier alnifolia). Rising a few meters above the surrounding plains, this hummocky knob and kettle terrain has a variety of wetlands scattered throughout. Elk Island National Park represents one of Canada’s 39 natural regions and has a wealth of unique biodiversity: over 40 native mammals, 200 species of birds, and 600 plants are found in Elk Island and in the Beaver Hills area (Parks Canada, 2004). Preserving a remnant herd of native elk was the driving force behind setting aside the park in 1906. The park’s 194 km2 was carved out of the 442 km2 Cooking Lake Forest Reserve established in 1899 to prevent settlers from burning valuable timber (MacDonald, 1994). Realizing the valuable preservation and recreation significance of the Beaver Hills, two other protected areas, the Cooking Lake Blackfoot Multiuse Area and Ministik Bird Sanctuary were also created from the Cooking Lake Forest Reserve (Table 1 lists the protected areas within the study area). More recently, these protected areas have taken a more ecological approach to their management. Elk Island, for example, has moved away from an ungulate dominated management approach toward a more ecosystem approach that recognizes the significance of all native species and their biodiversity. Land cover changes in the Beaver Hills over the past several decades have been driven primarily by agricultural development: clearing land for crop and pasture for cattle. Economic development in Edmonton and Strathcona County and a population increase in the region of 8.9% between 1986 and 1996 have driven industrial and urban expansion (Graham and McFarlane, 2001). The Beaver Hills region contains a number of protected areas, including Elk Island National Park, Ministik Bird
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Sanctuary, Cooking Lake/Blackfoot multi-use (recreation) area, and the Miquelon Lake protected area (Table 1). Elk Island National Park currently holds populations of six species that are designated as endangered, threatened or of special concern some of which are data deficient including: wood bison (Bison b. athabascae), Trumpeter swan (Cygnus buccinator), Loggerhead shrike (Lanius ludovicianus excubitorides), Blackthroated green warbler (Dendroica virens), Western toad (Bufo boreas), and Canadian toad (Bufo hemiophrys). These species have been assessed federally by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and provincially by the Alberta Endangered Species Conservation Committee (AESCC). 2.2. Satellite imagery and image preprocessing Land cover change and landscape fragmentation dynamics for all lands within 50 km of Elk Island National Park (EINP) were examined, including the city of Edmonton, Alberta. A 50 km buffer from the boundary of EINP was chosen in order to include enough of the private lands surrounding the Beaver Hills to make comparisons with regional deforestation/fragmentation trends. At the same time, this buffer was small enough to allow field data collection for the calibration and validation of the remote sensing component of this paper. Ground cover characterization and ground cover change maps were derived from the interpretation of Landsat Multi-Spectral Scanner (MSS—80 m resolution and 4 spectral bands) and Thematic Mapper (TM—28.5 m resolution and 7 spectral bands) satellite image data captured two decades apart from 1977 to 1998. The images were selected to provide the maximum temporal spread possible. Earlier Landsat images were available (1973), but a very high amount of horizontal banding in the images made them unsuitable for classification. Because the study area falls on the border between two scenes (TM path 42, rows 22 and 23), pairs of consecutive images were used from 1977 and 1998. There were no available pairs of cloud free scenes for the mid-late 80’s, so a pair was constructed using one 1986 image and one 1988 image (hereafter referred to as the 1987 scene). Cloud free images were unavailable between 1998 and 2001 when the ground truth data was collected. Summer images were used (when all deciduous trees have their leaves on,
Table 1 Status of different conservation area surrounding the Elk Island National Park Protected area
Habitat type protected
Level of protection
Elk Island National Park (194 km2) Ministik Bird Sanctuary (109 km2) Beaver Hill Lake (land: 70 km2 water: 125 km2) Cooking Lake Blackfoot Multiuse Area (100 km2) Miquelon Lake Protected Area (36 km2)
A (highest level of ecological protection)
Emphasis of ecosystem preservation for all native species as well as restoration and monitoring Individual species approach, emphasis on bird preservation
B B C D (lowest level of ecological protection)
Individual species approach, emphasis on bird preservation, little shore line protection from agriculture Multi-user approach with marginal concern with habitat restoration (hunting, dog sledding, hiking, grazing, oil and gas wells) Multi-user approach including land development, acreage subdivisions
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Table 2 Details on the satellite images used in this study Date (dd/mm/yyyy) 18/06/1977 18/06/1977 26/05/1986 19/08/1988 11/05/1998 16/08/1998 a
Sensor (Landsat) MSS MSS TM TM TM TM
Path/row a
45 /22 45a/23 42/22 42/23 42/22 42/23
RMS error (m)
Resolution (re-sampled) (m)
45 51 37 40 18 18
75 75 25 25 25 25
Equivalent to TM path 42.
June–September) to reduce sun-angle and phenological differences. Image details and dates are given in Table 2. All images were registered to a Universal Transverse Mercator (UTM) projection system: zone 12 north, spheroid GRS 1980, datum NAD 83. The 1977 images were resampled to a pixel size of 75 m (from 80 m) and all other images were re-sampled to 25 m. Orthorectification was not necessary due to the relatively low relief in the area. Atmospheric correction of the images was also not necessary because each image was classified independently (Song et al., 2001). The study area is smaller than a full Landsat scene, so after registration the images were trimmed to cover only the area of interest. Archived air photos were purchased to assess the classification accuracy of the 1977 and 1987 images. These photos were registered to 1:20,000 Alberta provincial vector data. To provide a visual verification, the photos were chosen in areas where significant land cover change was identified in satellite images. The time lag between the 1998 imagery and the ground truth collection was not considered to be significant enough to warrant the cost of purchasing aerial photographs for 1998. 2.3. Image classification The classification of the satellite images was based on the Alberta Ground Cover Characterization (AGCC) hierarchical method (Sa´nchez-Azofeifa et al., 2003b). This technique involves sequential separation of the feature pixels in the image into groups based on spectral characteristics. Spectral clusters were obtained by unsupervised classification using the algorithm Iterative Self-Organizing Data Analysis Technique (ISODATA). This method is a variation of the K-mean method in which clusters are formed with minimum spectral distance, and then cluster means are adjusted iteratively. Field data for the classification and verification of the land cover maps were obtained in two field trips during the late spring and early fall of 2001 (May and September). We recorded geographical coordinates, a description of the dominant vegetation and took photos of the site. Sites were chosen that were located at least 50 m from the edge of patches, in relatively homogeneous areas of at least one ha. In total, 1027 data points were recorded. The database of land cover points was randomly divided into two sets, creating one set for image calibration (529 points), and one set for verification/error
analysis of the classification (421 points). Classes extracted were: water, urban, crops/agriculture, range (natural and anthropogenic grasslands), and deciduous forest. From the 1977 and 1987 aerial photographs (the only years with available aerial photographs), we chose 236 random points for 1977 and 238 for 1987. A visual interpretation of land cover was recorded and compared with the land cover indicated by the classified image. To assess the accuracy of the classification of the 1998 imagery, the remaining field data points (those which were not used in the classification process) were compared with the classified image. A confusion matrix was generated and the accuracy statistics were estimates using the Kappa and Tau coefficients (Ma and Redmond, 1995). Kappa and Tau coefficients are known standard classification statistics used in land cover mapping. These two coefficients relate to the probability of having correctly classified a given pixel or polygon when compared with a random labeling. Of these two coefficients Tau is sometimes preferred over Kappa given its robustness (Ma and Redmond, 1995). Random checks for different classes (150 polygons in total) were conducted visually to verify whether a quantified land cover change was in fact ‘‘a change’’ and not an anomaly derived from inaccuracies in the different classifications used in this study. The annual rate of change of forest area (deforestation given in %/year) was calculated as r = (1/(t2 t1)) ln(A2/A1) where t = time and A = area (Puyravaud, 2003). Landscape metrics (class area, number of patches, mean and median patch size, standard deviation patch size, mean shape index, and Shannon’s diversity and evenness indices of all classes) were calculated for the entire study area, and for the Beaver Hills moraine only using Patch Analyst (Rempel, 2002). To determine the actual core area of each forest patch (i.e. the area not affected by edge-effects), we re-calculated the area of the patch by removing the area of forest within distances of 100 and 300 m from all edges or linear features. A review by Debinski and Holt (2000) found that edge effects could penetrate up to 300 m, but that species-specific avoidance distances can vary greatly (Jalkotzy et al., 1997). Mean patch core size, largest patch and the area greater than 300 ha were estimated for all core areas. To create the boundaries for the protected areas network all of the 1998 forest and wetland patches greater than 100 ha were selected as the largest, and therefore most significant, patches for conservation in the landscape. These patches were buffered at a distance of 500 m and 6 km.
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3. Results 3.1. Image classification and accuracy The overall accuracy for the land cover classification was estimated to be 95% for 1977, 91% for 1987, and 87% for 1998. Kappa and Tau statistics (Ma and Redmond, 1995) were 88% (e.g. the data was classified correct 88% of the time versus random assignment) for 1977, 80% and 82%, respectively for 1986/1988, and 82% for 1998. The accuracy of the change maps was estimated by the product of the accuracies of the original scenes, resulting in accuracy of 86% for 1977–1987, 79% for 1987–1998, and 83% for 1977–1998. These accuracies surpass Alberta’s provincial standards (75% overall accuracy) for mapping land use and land cover, using Landsat Thematic Mapper satellite information. Visual checks conducted using aerial photography between 1977 and 1987 on 150 selected 3 ha polygons detected as ‘‘change’’ during the land cover change analysis (1977–1987), indicated that these changes were actual changes on the ground in 95% of the cases. Observed problems occurred mostly in the
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wetland and water classes, an issue that is related to climatic conditions that tend to reduce or increase the problem around lakes. No such visual checks were possible between 1987 and 1998, given the lack of aerial photography during these years. 3.2. Land cover changes The percentage of the study area covered by croplands increased from 1977 to 1987 and remained stable at about 52% until 1998, whereas rangeland cover steadily decreased from 1977, occupying about 30% of the landscape by 1998 (Fig. 2a). The loss in rangeland appeared to be mainly due to conversion to croplands, with a net loss of about 60,000 ha in the first decade (Table 3). In the Beaver Hills subset of the study area more cropland was converted to rangeland than vice versa (Table 3). Wetlands and water were minor cover class components of the area (Fig. 2a). There was a net loss of wetlands in the first decade and a net gain in the second, whereas the reverse was true for water bodies (Table 3). Beaver Hills had a similar trend for water, but no change in wetland (Table 3).
Fig. 2. Land cover metrics for the Elk-Island region (50 km buffer area), southern Alberta, Canada. (a) Land cover proportion, (b) number of patches, (c) mean patch size distribution, (d) deviation in mean patch size, and (e) mean shape index.
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Table 3 Area (in hectares) for each land cover change class in the study area as a whole, and for the Beaverhills moraine separately Class
1977–88
1988–98
Study area No change Gain of urban Range to crop Crop to range Deforestation Afforestation Loss of wetland Gain of wetland Loss of water Gain of water
996709 4182 174163 114178 45671 23518 225 143 2274 4328
1977–88
1988–98
Beaver Hills 1111937 20621 90736 91515 15730 28063 149 334 4453 1852
252373 15 6416 7651 10098 7428 0 0 193 873
261851 338 3755 7202 2336 8841 0 0 460 263
Forest covered about 12% of the study area (Fig. 2a). There was a net loss of forest area (deforestation minus afforestation) between 1977 and 1987 (ca. 22,000 ha), followed by a gain in forest area from 1987 to 1998 (13,000 ha) in the study area (Table 3). A similar trend was observed for the Beaver Hills. Over the two decades, afforestation balanced deforestation in the study area, whereas much more land was afforested than deforested in the Beaver Hills. This increase in forest cover was associated with regeneration of lands initially utilized for croplands and range. Urban area also increased, mostly as result of the expansion of the City of Edmonton (Figs. 3 and 4; Table 3). Annual rates of deforestation, both in terms of deforestation, and in actual change in forest area (which accounts for afforestation), were higher from 1977 to 1987 than from 1987 to 1998 (Table 4). The rate of deforestation was higher in the entire study area than in the Beaver Hills. The largest single deforestation event was the clearing of the grazing leases in the Cooking Lake/Blackfoot area (within the Beaver Hills) between 1977 and 1987: 3036 ha were deforested, representing 30% of the 10,098 ha forest lost in the Beaver Hills. 3.3. Fragmentation metrics The number of patches increased over time in all land cover classes, with the largest increase occurring between 1987 and 1998 in the crop and range (Fig. 2b) category. There was a concomitant decrease in the mean patch size and the standard deviation in mean patch size over time for most cover classes (Fig. 2c and d). Values for shape index (higher values indicate more complex shape) peaked in 1987 (Fig. 2e). Shannon’s diversity index increased from 1.18 to 1.30 from 1977 to 1987 and then decreased to 1.27 in 1998, while evenness increased from 0.61 to 0.67 and then decreased to 0.65. Increase in Shannon’s evenness and diversity indices indicate an increase in both distribution and proportional distribution of land cover classes. The sharp decrease in mean patch size for the urban land cover class between 1977 and 1987 is the result of a change in resolution of the satellite imagery. The 1977 image does not resolve the small green spaces (parks and lawns) within the City
of Edmonton that are identifiable in the later imagery. This effect will not be significant outside of the city. The number of patches of forest steadily increased between 1977 and 1998 (Fig. 2b). Mean forest patch size decreased from 57 ha in 1977, 41 ha in 1987, to 30 ha in 1998. The 1998 forest landscape was very patchy, dominated by large tracts of crop and range. The core area of forest was calculated using buffers of 100 and 300 m from patch edges (Table 5). There was an overall decrease in core area between 1977 and 1987 (average decrease of 48%), with a rebound between 1987 and 1998 (average increase of 33%). Although, the largest patch and the area of patches greater than 300 ha were similar between 1977 and 1998, the largest patch of core forest and the area of core forest patches over 300 ha both declined over the two decades (Table 5). The results of buffering the 1998 forest and wetland patches of 100 ha and over at 0.5 and 6.0 km are shown in Fig. 5 as, respectively, the boundary for the buffer zone and the zone of cooperation. 4. Discussion and conclusion The Beaver Hills landscape has experienced a combination of land cover change processes: deforestation, fragmentation, and afforestation. The area of core forest patches greater than 300 ha has declined, with only 500 ha of core area (300 m buffer) remaining (Table 5), this is an 88% decrease since 1977. The increased fragmentation of the landscape (increased patch number, decreased patch size, higher shape index, increased diversity) correlates well with observed agricultural/economic trends for the County of Strathcona. Between 1981 and 1996, the number of crops and farms more than doubled the number of beef cows increased by 68%, and all other cattle increased by 38% (Toma and Bouma, 2003). Toma and Bouma (2003) concluded that there was an increase in small specialized agricultural operations and some extensive cattle operations, while the number of intensive livestock operations and traditional cropping operations declined, due in part to the high cost of land in the region. Afforestation in the Beaver Hills is in part a result of acreage and other landowners increasingly allowing their pastures to fill in with trees as well as the abandonment of marginal ranching/ farming operations and the subsequent natural conversion of the land back to forest. New forest is primarily composed of fast growing Trembling aspen (P. tremuloides), and to a lesser extent, Balsam Poplar (P. balsamifera) in wetter areas. The trees grow from the edges of pastures, often with underground rhizomes and/or from clumps within pastures that expand outward. In 2002, a 40 ha treed parcel adjacent to Elk Island National Park was logged. Within 3 years, the suckering Aspen poplars (P. tremuloides) are beginning once more to dominate the parcel through afforestation. Wetlands are largely fed by rainwater and so vary in size according to rainfall events. Some of the larger wetlands, such as shallow Tawayik Lake have shrunk by more than 10% over the course of the drought, which has lasted longer than the past 5 years.
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Fig. 3. Land cover for the Beaver Hill regions of Alberta: (a) 1977, (b) 1987, and (c) 1998. Cyan: Urban, Yellow: crops, Blue: water, Gold: range, Red: all forest types, Magenda: wetlands. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The situation in this study area is very similar to that presented by Hobson et al. (2002) for the southern edge of the boreal forest in Saskatchewan. In both cases, the majority of suitable lands have been converted to agriculture, there is a significant increase in afforestation as a result of land abandonment and a high rate of deforestation is observed as a result of cutting of forest patches. Similar patterns have been documented in Costa Rica (Van Laake and Sanchez-Azofeifa, 2004). The overall annual rate of deforestation in our region (accounting for secondary growth) is 0.27%, which is less than the 0.89% reported in Saskatchewan and very close to the 0.24% world average for all forests (FAO, 2001; Hobson et al., 2002). This figure masks a great deal of spatial and temporal
variation, however, with rates ranging from 2.38% deforestation in the lands surrounding the Beaver Hills between 1977 and 1987, to 2.00% afforestation in the Beaver Hills between 1987 and 1998. Examining regional trends also masks significant local events. The Blackfoot grazing leases were cut between 1980 and 1984 into the largest contiguous patch of forest that existed in the study area. The clearing resulted in an immediate and significant loss of core forest area and concomitant increase in fragmentation, both in terms of land cover and the associated roads and fences required for the grazing leases. In addition to the immediate impact of the clearing itself, grazing cattle can have significant impacts on vegetation (including damage to native species and
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Fig. 4. Land cover change Beaver Hill region. Red represents deforestation, green afforestation and Cyan increase in urbanization. (a) Land cover change 1977–1987, (b) Land cover change 1987–1998 and (c) Land cover change 1977–1998. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Table 4 Rate (%/year) of deforestation and change in total forest area (accounting for deforestation and afforestation) Time period
Study area Deforestation only
1977–1987 1987–1998
2.54 1.07
Beaver Hills Total change in forest area 1.74 1.35
Deforestation only 1.53 0.39
Total change in forest area 0.65 2.00
J.E. Young et al. / Forest Ecology and Management 230 (2006) 151–161 Table 5 Area of forest and core forest habitat, mean patch size, area of largest patch and area of all forest patches larger than 300 ha in the complete study area surrounding the Elk Island National Park, Alberta, Canada 1977
1987
1998
No buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area >300 (ha)
187000 57 35000 116000
155000 41 13000 90000
177000 30 36000 113000
100 m buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area >300 (ha)
67000 17 2000 15000
42000 14 1600 5000
50000 16 1600 8000
300 m buffer Total area (ha) Mean patch size (ha) Largest patch (ha) Area > 300 (ha)
11000 33 1100 4000
4600 21 500 500
6700 22 500 500
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invasion of exotic plants), bird and mammalian communities (due to habitat reduction or structural changes, spread of disease, and fencing), and water quality (due to damaged riparian vegetation and fecal contamination) (Coker and Capen, 1995; Donald et al., 1998; Jenkins and Parker, 2000). Networks of protected areas representing a diversity of communities are the best way to maintain biodiversity (Primack, 2002). Theories of island biogeography suggest that the size, shape, and connectivity of a reserve will impact its success at conserving ecological integrity (MacArthur and Wilson, 1967; Primack, 2002). The size of a park is the most critical factor in its ability to conserve biodiversity. The minimum reserve area required to conserve species diversity in parks in North American is on the order of 10,000 km2 (Newmark, 1995; Gurd et al., 2001; Wiersma, 2001), a reality that it is impossible to achieve in our study area. To overcome this problem, it may be possible to increase the effective area by using corridors and buffer zones that connect small-protected areas into a larger network (Gurd et al., 2001). The mean size of protected areas in the study area is 930 ha, much smaller that the 10,000 km2 minimum recommended size. If all of these protected areas were to become isolated, then the chances for maintaining the current diversity of species in the Beaver Hills would be slim.
Fig. 5. Example of a possible protected area network. Zones include the core areas (currently protected), the buffer zone (high conservation priority), and the zone of cooperation (sustainable development). Lighter gray areas of the image indicate cropland. Letter between parentheses refer to different levels of protection as per Table 1.
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A protected area network could be created in the study area, based on the UNESCO biosphere model (Fig. 5) (UNESCO, 1995). The network is composed of three zones: a core of strict habitat protection, a buffer of compatible use, and a zone of cooperation in which sustainable development is permitted within limitations based on compatibility with the conservation requirements. The five largest currently protected areas in the study area (Elk Island, Beaver Hill Lake, Cooking LakeBlackfoot, Ministik Lake, Miquelon Lake) are already clustered together due to their creation from the initial forest reserve and could form the core conservation area. A first estimation of the boundaries for the buffer zone and zone of cooperation was established based on buffers around the largest patches of forest and wetland, but the actual zone boundaries would depend on variables including location of rare or endangered species and the degree of cooperation from local stakeholders. Rehabilitation of at least one of the central grazing plots in the Blackfoot multi-use area at the Cooking Lake/Blackfoot region (Fig. 5) would improve connectivity between the remaining core areas. A buffer zone around Elk Island and the other protected areas must be assessed as well. The significance of the terrestrial and wetland habitats in the Beaver Hills provide justification for application for joint protection under the UNESCO Man and the Biosphere (MAB) program and the RAMSAR Convention on Wetlands (MAB, 2002). To be successful, the proposed UNESCO biosphere model must address the fact that the creation of additional national parks in this fragmented ecosystem is not realistic and that Elk Island National Park has become systematically more isolated from the forest matrix. Instead, the development of biological corridors and the promotion of private reserves, under a scheme for payments for environmental services (PES), is a more realistic option for conservation. Experiences, such as those developed by the Costa Rica National Financing Fund (FONAFIFO) aimed to promote conservation under PES must be studied before they are implemented in the boreal forest/ aspen parkland. Efforts by organizations, such as the Nature Conservancy of Canada that already operate in the Beaver Hills acquiring land covenants for conservation must be expanded as well. Acknowledgements We would like to thank Elk Island National Park for data and logistical support. The Canada Foundation for Innovation (CFI) and the National Network of Centers of Excellence: Sustainable Forest Management Network (NCE-SFMN) also provided support for this research initiative. References Alberta Environmental Protection, 1998. The Boreal forest natural region of Alberta. Unpublished report for the Special Places 2000 Provincial Coordinating Committee. Bonan, G.B., Shugart, H.H., 1989. Environmental factors and ecological processes in boreal forests. Anual Rev. Ecol. Syst. 20, 1–28.
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