David M. Theobald

RURAL LAND-USE TRENDS IN THE CONTERMINOUS UNITED STATES, 1950-2000

In order to understand the magnitude, direction, and geographic distribution of land-use changes, we evaluated land-use trends in U.S. counties during the latter half of the 20th century. Our paper synthesizes the dominant spatial and temporal trends in population, agriculture, and urbanized land uses, using a variety of data sources and an ecoregion classification as a frame of reference. A combination of increasing attractiveness of nonmetropolitan areas in the period 1970-2000, decreasing household size, and de- creasing density of settlement has resulted in important trends in the patterns of developed land. By 2000, the area of low-density, exurban development beyond the urban fringe occupied nearly 15 times the area of higher density urbanized development. Efficiency gains, mechanization, and agglomeration of agricultural concerns has resulted in data that show cropland area to be stable throughout the Corn Belt and parts of the West between 1950 and 2000, but decreasing by about 22% east of the Mississippi River. We use a regional case study of the Mid-Atlantic and Southeastern regions to focus in more detail on the land-cover changes resulting from these dynamics. Dominating were land-cover changes associated with the timber practices in the forested plains ecoregions and urban- ization in the piedmont ecoregions. Appalachian ecoregions show the slowest rates of land- cover change. The dominant trends of tremendous exurban growth, throughout the United States, and conversion and abandonment of agricultural lands, especially in the eastern United States, have important implications because they affect large areas of the country, the functioning of ecological systems, and the potential for restoration.

Estimating the cumulative effects of development on wildlife habitat

The cumulative effects problem in natural resource management and land use planning stems from the difficulty of demonstrating that while each single land use change results in a negligible impact, the accumulation of these individual changes over time and within a landscape or region may constitute a major impact. This paper details a general approach to estimate the cumulative effects of land use change on wildlife habitat using Summit County, CO, USA as a case study. Our approach is based on a functional relationship between effect on habitat and distance from development. Within this building-effect distance, habitat is assumed to be degraded, producing a disturbance zone. We sum the total area within the disturbance zone and track how it changes over time and in response to different land use planning actions. This method is sensitive to both housing density and spatial pattern, so that the relative effects of clustered development can be evaluated. Two factors are important in understanding how development potentially degrades habitat: alteration of habitat near buildings and roads and landscape fragmentation. Our results show clustered development reduces the negative impacts on wildlife habitat. For large building-effect distances, spatial pattern was found to be a stronger indicator of disturbance than density. Efforts to decrease habitat disturbance by lowering development density should include the regulation of subdivision pattern in addition to decreasing density.

Incorporating biological information in local land-use decision making: designing a system for conservation planning

Human settlement is a formidable agent of change affecting fundamental ecological processes. Decisions governing these land-use changes occur almost exclusively at the local level and, as a result, they are made at many different locations and times. Consequently, it is difficult for ecologists to provide needed scientific support for these choices. We built an information system designed to support conservation decisions at local scales by offering data over the Internet. We collaborated with local stakeholders (e.g., developers, planners, politicians, land owners, environmental activists) to design the system. This collaboration produced several generalizations about effective design of information systems to support conservation. The most important of these is the idea that ecological data and analysis must be understood by those who will be affected by the decisions. Also, planning for conservation is a process that uses scientific data, but that ultimately depends on the expression of human values. A major challenge landscape ecologists face is to extend general landscape principles to provide specific scientific information needed for local land-use planning.

Placing exurban land‐use change in a human modification framework

Emerging research on human-modified ecosystems can better inform land-use planning by integrating information from ecological and social science. In particular, low-density land use beyond the urban fringe (exurban) has been poorly defined and under-studied. Here I develop the human modification framework that characterizes landscapes by the degree to which natural processes are free or controlled and landscape patterns are natural or artificial. Ecologists are encouraged to explicitly place their researchwithin such a framework using quantitative metrics. As societys concern over ecological degradation and loss of biodiversity grows, ecologists must recognize that research on human-modified landscapes, particularly beyond the urban fringe, is not just an unexploited opportunity, but is critical to protecting biodiversity on private land.

Spatial statistical models that use flow and stream distance

We develop spatial statistical models for stream networks that can estimate relationships between a response variable and other covariates, make predictions at unsampled locations, and predict an average or total for a stream or a stream segment. There have been very few attempts to develop valid spatial covariance models that incorporate flow, stream distance, or both. The application of typical spatial autocovariance functions based on Euclidean distance, such as the spherical covariance model, are not valid when using stream distance. In this paper we develop a large class of valid models that incorporate flow and stream distance by using spatial moving averages. These methods integrate a moving average function, or kernel, against a white noise process. By running the moving average function upstream from a location, we develop models that use flow, and by construction they are valid models based on stream distance. We show that with proper weighting, many of the usual spatial models based on Euclidean distance have a counterpart for stream networks. Using sulfate concentrations from an example data set, the Maryland Biological Stream Survey (MBSS), we show that models using flow may be more appropriate than models that only use stream distance. For the MBSS data set, we use restricted maximum likelihood to fit a valid covariance matrix that uses flow and stream distance, and then we use this covariance matrix to estimate fixed effects and make kriging and block kriging predictions.

National housing and impervious surface scenarios for integrated climate impact assessments

Understanding the impacts of climate change on people and the environment requires an understanding of the dynamics of both climate and land use/land cover changes. A range of future climate scenarios is available for the conterminous United States that have been developed based on widely used international greenhouse gas emissions storylines. Climate scenarios derived from these emissions storylines have not been matched with logically consistent land use/cover maps for the United States. This gap is a critical barrier to conducting effective integrated assessments. This study develops novel national scenarios of housing density and impervious surface cover that are logically consistent with emissions storylines. Analysis of these scenarios suggests that combinations of climate and land use/cover can be important in determining environmental conditions regulated under the Clean Air and Clean Water Acts. We found significant differences in patterns of habitat loss and the distribution of potentially impaired watersheds among scenarios, indicating that compact development patterns can reduce habitat loss and the number of impaired watersheds. These scenarios are also associated with lower global greenhouse gas emissions and, consequently, the potential to reduce both the drivers of anthropogenic climate change and the impacts of changing conditions. The residential housing and impervious surface datasets provide a substantial first step toward comprehensive national land use/land cover scenarios, which have broad applicability for integrated assessments as these data and tools are publicly available.

LAND USE AND LANDSCAPE CHANGE IN THE COLORADO MOUNTAINS I: THEORY, SCALE, AND PATTERN

Residential and commercial land development quickened during the 1990s throughout the U.S. Rocky Mountains, especially in Colorado, increasing the pace and extent of regional land use and landscape change. Unlike previous booms in mining, cattle, or energy, the current development wave is driven by growth in the secondary and tertiary economies--services, recreation, and information businesses-instead of commodity production. The result is sprawling land-use conversion, mostly from agricultural to residential, in even the most rural areas. This development pattern is examined in light of mountain and rural land-use theory, and its effects are evaluated at three scales in the Colorado mountains-regional, landscape, and site. The social and ecological impacts cited in previous rural development literature are evident, but also documented are landscape effects associated with the particular affluence of Colorado mountain development and the emergence of far-reaching rural sprawl and gentrification. Current development tends more than in the past to fragment land ownership, steepen land-use gradients at public/private boundaries, and increase human presence and disturbance in the urban/wildland interface. The paper concludes with suggestions for planning focused at the landscape scale.

EFFECTS OF HUMAN SETTLEMENT ON BIRD COMMUNITIES IN LOWLAND RIPARIAN AREAS OF COLORADO (USA)

Riparian areas in western North America have been characterized as centers of avian diversity, yet little is known about the ways that native species in streamside habitats are affected by development nearby. To address this issue, we examined patterns of habitat use by birds during the 1995-1997 breeding seasons at 16 lowland riparian sites representing an urban-to-rural gradient. As development increased, riparian woodlands tend- ed to have fewer native trees and shrubs, less ground and shrub cover, higher tree densities, and greater canopy closure. Bird species richness also declined as urbanization increased in the surrounding landscape. Canonical correspondence analysis (CCA) revealed that mea- sures of settlement intensity best explained variation in habitat use by riparian birds, al- though some residual variation was accounted for by differences in woodland understory features. Migrant and low-nesting species were associated with lower-than-average levels of development, whereas resident and cavity-nesting species tended to increase with ur- banization. In partial CCA analyses, however, local habitat variables explained twice the variation that measures of settlement did; nearly half of all explained variation could be attributed to local and landscape variables simultaneously. For avian guilds based on mi- gratory, nesting, and foraging behavior, regression analyses showed that the best variables for explaining patterns of habitat use were usually those that reflected levels of urbanization, particularly at broad scales. When the effects of local habitat variation were removed, however, the best variables for explaining residual variation in habitat use tended to describe development at relatively fine scales, especially for species that nested or foraged low for insects or seeds. These species were also the most sensitive to human trail use. Our analyses indicated that bird communities and local habitat conditions in riparian areas were both affected by development in the surrounding landscape. It may be possible to mitigate the negative impacts of human settlement on native birds in streamside woodlands by main- taining or restoring vegetation structure and composition, and by imposing limits on human recreational activity in these habitats.

Spatial population genetic structure and limited dispersal in a Rocky Mountain alpine stream insect

Using the mitochondrial cytochrome oxidase I (COI) gene, we assessed the phylogeographic structure of Prosimulium neomacropyga, a black fly (Simuliidae) whose distribution in the US Southern Rockies ecoregion is limited to alpine tundra streams. Given high habitat specificity, lack of hydrological connection between streams, and a terrestrial environment restrictive to insect flight, we hypothesized limited gene flow. A spatially nested sampling design showed that grouping populations according to high‐elevation ‘islands’ of alpine tundra (which typically include headwater streams of > 1 watershed) explained a significant proportion of genetic variation while grouping streams according to major watershed (across islands) did not. Nested clade analysis and isolation‐by‐distance (IBD) relationships further implicated limited ongoing gene flow within but not among the isolated alpine islands. IBD was strong among five streams within an individual island using each of four alternative models of pairwise landscape connectivity for flying insects. Results of all landscape models were positively correlated, suggesting that straight‐line distance is an acceptable surrogate for presumably more biologically meaningful connectivity measures in this system. IBD was significantly weaker across the entire study area, comprised of three separate islands. Overall, population structure was significant with FST = 0.38, suggesting limited dispersal across a small spatial extent.

Modelling dendritic ecological networks in space: an integrated network perspective

Dendritic ecological networks (DENs) are a unique form of ecological networks that exhibit a dendritic network topology (e.g. stream and cave networks or plant architecture). DENs have a dual spatial representation; as points within the network and as points in geographical space. Consequently, some analytical methods used to quantify relationships in other types of ecological networks, or in 2-D space, may be inadequate for studying the influence of structure and connectivity on ecological processes within DENs. We propose a conceptual taxonomy of network analysis methods that account for DEN characteristics to varying degrees and provide a synthesis of the different approaches within the context of stream ecology. Within this context, we summarise the key innovations of a new family of spatial statistical models that describe spatial relationships in DENs. Finally, we discuss how different network analyses may be combined to address more complex and novel research questions. While our main focus is streams, the taxonomy of network analyses is also relevant anywhere spatial patterns in both network and 2-D space can be used to explore the influence of multi-scale processes on biota and their habitat (e.g. plant morphology and pest infestation, or preferential migration along stream or road corridors).