Exurban Development Research Articles

Towards a Polycentric Region? The Socio‐economic Trajectory of Rome, an ‘Eternally Mediterranean’ City

AbstractThe present study explores the long‐term changes (1971–2001) in the socio‐economic structure of a monocentric Mediterranean urban region (Rome's province, central Italy) undergoing moderately polycentric development. Descriptive and correlation statistics and a multiway factor analysis (MFA) have been used to analyse the spatio‐temporal evolution of 24 socio‐economic indicators made available at the urban district/municipal scale. The socio‐economic disparities observed along the urban‐rural gradient in 1971 decreased only moderately in 2001. The MFA clearly separates urban districts from suburban municipalities in both 1971 and 2001. Results indicate that exurban development has impacted only partly Rome's urban form which remained mainly compact and dense with persisting socio‐economic gaps between urban and suburban areas. The paper discusses the partial failure of Rome's master plan to promote a really polycentric development and a new, more sustainable, urban form.

Exurban Development and Landscape Diversification in a Mediterranean Suburban Area

This study explores the relationship between landscape diversification and exurban development in a mono-centric compact urban region in transition toward a more diffused (and possibly polycentric) form. Based on the spatial distribution of seven land-use classes derived from comparable digital maps for 1975, 1990, 2000 and 2009, a spatial analysis integrated with correlation and multivariate statistical techniques was developed to verify if exurban development influenced landscape composition and structure in Attica, the region where Athens, the capital of Greece, is located. Results showed the different land-use distributions before and after dispersed urban expansion. Both urban areas and bare land increased rapidly during the last 35 years with implications for landscape quality and diversity. To the contrary, rainfed cropland and sparsely vegetated areas experienced the highest probability to edification. At the regional scale, the landscape diversification index decreased weakly over time while increasing the positive correlation with the distance from the city center. As an indirect effect of dispersed urbanization, the highest contribution to landscape diversity came from forests and natural areas and from the agricultural mosaic and cropland respectively in 1975 and 2009. The analysis illustrates how containing changes in land-use can be a target for policies mitigating landscape fragmentation in expanding urban regions.

Mapping Exurban Development: Can Road and Census Data Act as Surrogates?

Exurban development, characterized by low-density residential development, is one of the leading anthropogenic causes of land transformation. A major obstacle to studying this phenomenon is a lack of spatially explicit data. In this article, two commonly employed indirect approaches that use readily available road and census data as surrogates of exurban development are examined for their ability to delineate exurban development across large spatial extents. The study area is the heterogeneous exurban region of Peterborough County, Ontario, Canada. Comparing correlations between road density–based maps, dasymetric dwelling-count maps, and the reference data at multiple scales produced mixed results. Of the two methods, road density generally performed better, except when the census units were of relatively small size. Overall, the results highlight the way in which heterogeneity within a large study area can greatly obscure surrogate relationships that may be evident at smaller spatial extents, where conditions are relatively more homogeneous, making the use of these indirect methods challenging for large spatial extents. In particular, the geographic and historic context of the study area significantly influences the effectiveness of these methods, which should therefore be used with caution in mapping exurban development.

Urban containment in action? Long-term dynamics of self-contained urban growth in compact and dispersed regions of southern Europe

The present study illustrates an indicator of self-contained urban growth derived from official statistics with the aim of verifying if a shift from compactness towards settlement diffusion has occurred in cities with different socioeconomic and morphological characteristics. According to this approach, changes in settlement's distribution and density were assessed in four Mediterranean cities (Lisbon, Barcelona, Rome, and Athens) during 80 years between 1919 and 2001. Results indicated that settlement distribution, building density and self-contained urban growth diverged in the four regions since the early 1980s. However, cities with a compact form showed an higher self-contained growth rate than cities with dispersed form. These findings contrast with the similarity in settlement characteristics, population trends, and spatial organization of economic activities observed during the ‘compact growth’ phase (1950–1980) in all examined regions. Comparative analyses of exurban development through morphological indicators may inform strategies promoting self-contained urban growth.

Threshold Responses of Forest Birds to Landscape Changes around Exurban Development

Low-density residential development (i.e., exurban development) is often embedded within a matrix of protected areas and natural amenities, raising concern about its ecological consequences. Forest-dependent species are particularly susceptible to human settlement even at low housing densities typical of exurban areas. However, few studies have examined the response of forest birds to this increasingly common form of land conversion. The aim of this study was to assess whether, how, and at what scale forest birds respond to changes in habitat due to exurban growth. We evaluated changes in habitat composition (amount) and configuration (arrangement) for forest and forest-edge species around North America Breeding Bird Survey (BBS) stops between 1986 and 2009. We used Threshold Indicator Taxa Analysis to detect change points in species occurrence at two spatial extents (400-m and 1-km radius buffer). Our results show that exurban development reduced forest cover and increased habitat fragmentation around BBS stops. Forest birds responded nonlinearly to most measures of habitat loss and fragmentation at both the local and landscape extents. However, the strength and even direction of the response changed with the extent for several of the metrics. The majority of forest birds’ responses could be predicted by their habitat preferences indicating that management practices in exurban areas might target the maintenance of forested habitats, for example through easements or more focused management for birds within existing or new protected areas.

Effects of Exurban Development and Temperature on Bird Species in the Southern Appalachians

Land-use dynamics and climatic gradients have large effects on many terrestrial systems. Exurban development, one of the fastest growing forms of land use in the United States, may affect wildlife through habitat fragmentation and building presence may alter habitat quality. We studied the effects of residential development and temperature gradients on bird species occurrence at 140 study sites in the southern Appalachian Mountains (North Carolina, U.S.A.) that varied with respect to building density and elevation. We used occupancy models to determine 36 bird species' associations with building density, forest canopy cover, average daily mean temperature, and an interaction between building density and mean temperature. Responses varied with habitat requirement, breeding range, and migration distance. Building density and mean temperature were both included in the top occupancy models for 19 of 36 species and a building density by temperature interaction was included in models for 8 bird species. As exurban development expands in the southern Appalachians, interior forest species and Neotropical migrants are likely to decline, but shrubland or edge species are not likely to benefit. Overall, effects of building density were greater than those of forest canopy cover. Exurban development had a greater effect on birds at high elevations due to a greater abundance of sensitive forest-interior species and Neotropical migrants. A warming climate may exacerbate these negative effects.

Mapping Multiple Forest Threats in the Northwestern United States

US forestlands are increasingly subject to disturbances including wildfire, insects and disease, and urban and exurban development. Devising strategies for addressing these “forest threats” depends on anticipating where individual disturbances are most likely and where they might occur in combination. However, many spatial data sets describing forest threats are produced at fine scales but are intended only for coarse-scale planning and policy purposes. We demonstrate one way to combine and display forest threat data at their appropriate spatial scales, using spatial data characterizing wildfire, insects and disease, and urban and exurban development in the northwestern United States. We use a novel 25-km radius neighborhood analysis to highlight locations where threats may be more concentrated relative to others and to identify where multiple threats intersect. Such neighborhood analyses and overlays can help policymakers and managers to anticipate and weigh the implications of potential threats and their intersections in regional- and national-level assessments.

Latent Exurban Development: City Expansion Along the Rural-To-Urban Gradient in Growing and Declining Regions of Southern Europe

This paper quantifies the extent of exurban development in Mediterranean Europe. The assessment was carried out by studying changes in the urban-to-rural population density gradient between the years 1950 and 2010. Three of the six urban regions in this study have experienced population growth and moderate urban concentration, while two regions appear to be shifting toward population decline and urban de-concentration after having experienced compact expansion. A phase of recent re-urbanization has been observed in one region. Altogether, these findings indicate a common path of urban expansion among representative Mediterranean regions between 1950 and 1980 while, in the following period, the cities experienced distinct development phases. From this study, we conclude that exurban development is mainly the product of a shift from compact and dense to semi-compact and intermediate-density settlements. [Key words: semi-dense urban growth, density-distance curve, Mediterranean Europe].

Symposium 9: Rocky Mountain Futures: Preserving, Utilizing, and Sustaining Rocky Mountain Ecosystems

Symposium 9: Rocky Mountain Futures: Preserving, Utilizing, and Sustaining Rocky Mountain Ecosystems

Size of the ecological effect zone associated with exurban development in the Adirondack Park, NY

Exurban development represents a potential threat to wildlife communities and ecological integrity in rural landscapes worldwide and recent work has suggested that its ecological impacts can be similar to those associated with more characteristically urban development patterns. Despite the large scope and rapid pace of exurbanization, understanding of its ecological consequences is incomplete and most North American research has occurred in the western United States. The ecological impact zone denotes the area surrounding a home which should be considered affected habitat and has been shown to be demonstrably larger than the actual footprint of homes and lawns. We conducted a study to determine whether an impact zone of 180m identified for a shrub-oak community in the Rocky Mountain west was applicable in an eastern, closed forest system. We sampled bird communities at the forest/lawn edge of exurban homes, and at 200- and 400-m in surrounding forest and modeled occupancy at increasing distances from residential structures for human-adapted, human-sensitive, and neutral species. Occupancy rates of human-adapted and human-sensitive species were different (36% higher and 26% lower, respectively) at points near homes versus those in surrounding forest. Our findings indicate a similarity in the effects of exurban homes on avian communities and the size of the ecological impact zone in these structurally different eastern and western North American landscapes. This similarity suggests the possibility that human behaviors associated with exurban homes may play a larger role in shaping avian community characteristics nearby than do habitat alterations created by construction and clearing.

Between a rock and a hard place: the impacts of climate change and housing development on breeding birds in California

Although the effects of climate change on species distributions have received considerable attention, land-use change continues to threaten wildlife by contributing to habitat loss and degradation. We compared projected spatial impacts of climate change and housing development across a range of housing densities on California’s birds to evaluate the relative potential impacts of each. We used species-distribution models in concert with current and future climate projections and spatially explicit housing-development density projections in California. We compared their potential influence on the distributions of 64 focal bird species representing six major vegetation communities. Averaged across GCMs, species responding positively to climate change were projected to gain 253,890 km2 and species responding negatively were projected to lose 335,640 km2. Development accounted for 32 % of the overall reductions in projected species distributions. In terms of land area, suburban and exurban development accounted for the largest portion of land-use impacts on species’ distributions. Areas in which climatic suitability and housing density were both projected to increase were concentrated along the foothills of the Sierra Nevada and areas of the north coast. Areas of decreasing climatic suitability and increasing housing density were largely concentrated within the Central Valley. Our analyses suggest that the cumulative effects of future housing development and climate change will be large for many bird species, and that some species projected to expand their distributions with climate change may actually lose ground to development. This suggests that a key climate change adaptation strategy will be to minimize the impacts of housing development. To do this effectively, comprehensive policies to guide land use decisions are needed at the broader scales of climate change.

WUI Space

This essay explores the ways we talk about water and fire in California, how that discussion is shaped by larger ecological and economic concerns, and how those concerns in turn shape exurban development in the state.

Impacts of rural development on Yellowstone wildlife: linking grizzly bear Ursus arctos demographics with projected residential growth

Exurban development is consuming wildlife habitat within the Greater Yellowstone Ecosystem with potential consequences to the long‐term conservation of grizzly bears Ursus arctos. We assessed the impacts of alternative future land‐use scenarios by linking an existing regression‐based simulation model predicting rural development with a spatially explicit model that predicted bear survival. Using demographic criteria that predict population trajectory, we portioned habitats into either source or sink, and projected the loss of source habitat associated with four different build out (new home construction) scenarios through 2020. Under boom growth, we predicted that 12 km2 of source habitat were converted to sink habitat within the Grizzly Bear Recovery Zone (RZ), 189 km2 were converted within the current distribution of grizzly bears outside of the RZ, and 289 km2 were converted in the area outside the RZ identified as suitable grizzly bear habitat. Our findings showed that extremely low densities of residential development created sink habitats. We suggest that tools, such as those outlined in this article, in addition to zoning and subdivision regulation may prove more practical, and the most effective means of retaining large areas of undeveloped land and conserving grizzly bear source habitat will likely require a landscape‐scale approach. We recommend a focus on land conservation efforts that retain open space (easements, purchases and trades) coupled with the implementation of ‘bear community programmes’ on an ecosystem wide basis in an effort to minimize human‐bear conflicts, minimize management‐related bear mortalities associated with preventable conflicts and to safeguard human communities. Our approach has application to other species and areas, and it has illustrated how spatially explicit demographic models can be combined with models predicting land‐use change to help focus conservation priorities.

Impacts of residential development on ungulates in the Rocky Mountain West

AbstractRural residential development in the Rocky Mountain West of North America is resulting in increased conflict between ungulate habitat and infrastructure. Subdivisions, houses, and roads affect ungulates both behaviorally and demographically and reduce management options available to agencies. These habitat alterations need to be addressed if wildlife species are to coexist with humans. We reviewed literature (using 7 search engines and 16 key words) on the effects of land‐use change (especially residential development) on elk (Cervus canadensis), mule deer (Odocoileus hemionus), white‐tailed deer (O. virginianus), American pronghorn (Antilocapra americana), and bighorn sheep (Ovis canadensis). Approximately 80 studies were directly related to the effects of human development on ungulates; however, only 25 specifically examined residential development and its influences on the focal species. Studies varied in methodology (i.e., aerial and ground surveys, pellet counts, movement rates) and analyses. The literature suggests most ungulates exhibit short‐term behavioral reactions to human disturbance. However, few studies link these responses to population‐level consequences or test the cumulative impact that multiple developments and development types (i.e., roads, housing, industrial development) have on seasonal habitat use and migratory behavior. Short‐term and small‐scale observational studies have articulated the conflict between humans and ungulates on shared habitat. Those studies need to be followed with well‐designed experiments and large‐scale multi‐jurisdictional projects so that managers and planners can make more credible recommendations to direct future exurban development that benefits wildlife and humans. © 2012 The Wildlife Society.

Local- versus landscape-scale effects on the demography of three forest-breeding songbirds in Ontario, Canada

Reproductive success of songbirds breeding in forest fragments can be influenced by local habitat characteristics and by anthropogenic land uses in the surrounding matrix such as exurban development and agriculture. Effectively managing these songbirds requires an understanding of which spatial scales most strongly influence their demography. We conducted a multiscale study to investigate the relative influence of local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) in a predominantly agricultural landscape on songbird demography. Density, pairing success, nest success, and productivity were assessed for Ovenbirds ( Seiurus aurocapilla (L., 1766)), Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)), and American Robins ( Turdus migratorius L., 1766) in 16 deciduous forest fragments in southeastern Ontario. Demography of Ovenbirds was most strongly associated with local vegetation characteristics, while demography of Wood Thrush and American Robins was most strongly related to landscape composition within a 2000 m buffer. For all three species, cross-scale correlations influenced nest success, although other demographic parameters were less affected. We conclude that relationships between local- and landscape-scale metrics and songbird demography are complex, species-specific, and differ among reproductive parameters, necessitating a multiscale approach to management.

Modeling exurban development near Washington, DC, USA: comparison of a pattern-based model and a spatially-explicit econometric model

The development of private rural lands can significantly fragment landscapes, with potentially negative consequences on ecosystem services. Models of land-use trends beyond the urban fringe are therefore useful for developing policy to manage these environmental effects. However, land-use change models have been primarily applied in urban environments, and it is unclear whether they can adequately predict exurban growth. This study compared the ability of two urban growth models to project exurban development in north-central Virginia and western Maryland over a 24-year period. Pattern-based urban growth models (such as SLEUTH) are widely used, but largely mimic patterns that emerge from historic conditions rather than allowing landowner decision-making to project change. In contrast, spatially-explicit econometric models (such as the complementary log–log hazard assessed in this study) model landowner choices as profit-maximizing behavior subject to market and regulatory constraints. We evaluated the two raster-based models by comparing model predictions to observed exurban conversion at pixel and county scales. The SLEUTH model was more successful at matching the total amount of new growth at the county scale than it was at the pixel scale, suggesting its most appropriate use in exurban areas is as a blunt instrument to forewarn potential coarse-scale losses of natural resources. The econometric model performed significantly better than SLEUTH at both scales, although it was not completely successful in fulfilling its promise of projecting changes that were sensitive to policy. The lack of significance of some policy variables may have resulted from insufficient variation in drivers over our study area or time period, but also suggests that drivers of land use change in exurban environments may differ from those identified for urban areas.

Exurban development derived from Landsat from 1986 to 2009 surrounding the District of Columbia, USA

People's preference for living in rural areas is converting rural landscapes into low-density residential development (i.e., exurban development). To assess the environmental impacts of exurban development (e.g., habitat fragmentation, threats to wildlife, and increased demand for natural resources), accurate maps of its spatial extent and change over time are needed. Mapping technologies that are based on remote sensing spectral data alone have generally failed to separate exurban development from the surrounding landscape and from other mixed pixels with similar spectra. Although deciduous forests in the eastern United States are thought to have experienced a significant increase in exurbanized area, a rigorous assessment of exurban trends has yet to be undertaken. The purpose of this study was to develop a novel analytic approach to map exurban development and to assess its magnitude and rate in north-central Virginia and western Maryland. We applied spectral mixture analysis to Landsat TM images from 1986 to 2009 at 4 time steps to estimate the fractional cover of vegetation, shade, substrate, and non-photosynthetic vegetation endmembers within each image. Using training data based on aerial photos, we classified the resulting endmember fraction images using a decision tree. Finally, terminal nodes from the decision tree that did not differentiate between exurban and urban areas were analyzed using morphological spatial pattern analysis to assess the shape and form of landscape elements. Scattered, isolated pixels were considered representative of exurban development. Overall classification accuracies ranged from 93 to 98%, an improvement of up to 34% over the decision tree alone. Our mapping approach effectively identified 7.3% of north-central Virginia and western Maryland as exurban development. Exurban development had a substantial expansion in the region, increasing on average 6.1% per year between 1986 and 2009. The mapping of land-cover changes beyond urban fringe provides valuable information for policymakers, planners, and land managers tasked with managing and mitigating the potential adverse consequences of this increasingly common form of landscape change.

Effects of Climate and Exurban Development on Nest Predation and Predator Presence in the southern Appalachian Mountains (U.S.A.)

In the eastern United States, land-use and climate change have likely contributed to declines in the abundance of Neotropical migrant birds that occupy forest interiors, but the mechanisms are not well understood. We conducted a nest-predation experiment in southern Appalachian Mountain forests (North Carolina, U.S.A.) during the 2009 and 2010 breeding seasons to determine the effects of exurban development and temperature on predator presence and the average number of days until eggs in an artificial nest were disturbed by predators. We baited artificial nests with quail (Excalfactoria chinensi) eggs and monitored them for 18 days. We used clay eggs, track plates, and motion-triggered cameras to detect and identify nest predators. The average number of days a nest was undisturbed decreased as mean temperature increased and, to a lesser extent, as the density of buildings increased. Nests on the ground were more often depredated than those in trees, likely due to increased predation by opossum (Didelphis virginiana) and other carnivores. Raccoons (Procyon lotor), opossums, corvids (Corvus brachyrhynchos and Cyanocitta cristata), chipmunks (Tamias striatus), black bears (Ursus americanus), and domestic cats (Felis catus) were the most commonly detected predators. Presence of these predators did not vary as a function of mean temperature. Domestic cats and corvids were detected more frequently in plots with high rather than low densities of buildings. Forest-interior specialists and Neotropical migrants often nest in cool, high-elevation areas with low housing density. These bird species, especially those that nest on the ground, may be most vulnerable to increased nest predation if temperature and exurban development increase at higher elevations as anticipated.

Exurban sprawl increases the extinction probability of a threatened tortoise due to pet collections

Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors’ own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations.

Carbon Stock Changes in Soil and Aboveground Biomass from House Lot Development in King County, Washington, USA

Fossil fuel burning and deforestation have driven dramatic increases in atmospheric CO2 since the industrial revolution. However, forests in the northern temperate region sequester a substantial (~0.6 Pg?yr–1) amount of carbon (C), largely through the regrowth of secondary forests that were originally cleared for timber over one hundred years ago. In the United States, however, some regions are approaching a maximum regrowth as forests are cleared again, this time for suburban and exurban development. Here we explore the effects of such development on C stocks in King County, WA, an area with high forest cover but rapid suburban expansion. We measured soil and biomass C on 18 paired-house/forest lots, and found house lots stored ~80 Mg?C?ha–1 less soil C, and between 130 and 280 Mg?C?ha–1 less above-ground biomass C than adjacent forest lots. Combining soil C losses with estimates of C emissions from forest products yields average C emissions of 130 - 280 Mg?C?ha–1, with the majority of losses occurring at the time of lot conversion. As a comparison, suburban dwellers drive ~30% more than city residents, but this increase in annual emissions from increased driving is 1% - 2.5% of the losses of C associated with converting forests to house lots. If forestland conversion in the Seattle area continues apace, in the coming decades C emissions each year from that land-use conversion will equal ~4% of King County’s 2008 C emissions.