Showing papers in "Landscape Ecology in 1990"

Spatial and temporal analysis of landscape patterns

Abstract: A variety of ecological questions now require the study of large regions and the understanding of spatial heterogeneity. Methods for spatial-temporal analyses are becoming increasingly important for ecological studies. A grid cell based spatial analysis program (SPAN) is described and results of landscape pattern analysis using SPAN are presentedd. Several ecological topics in which geographic information systems (GIS) can play an important role (landscape pattern analysis, neutral models of pattern and process, and extrapolation across spatial scales) are reviewed. To study the relationship between observed landscape patterns and ecological processes, a neutral model approach is recommended. For example, the expected pattern (i.e., neutral model) of the spread of disturbance across a landscape can be generated and then tested using actual landscape data that are stored in a GIS. Observed spatial or temporal patterns in ecological data may also be influenced by scale. Creating a spatial data base frequently requires integrating data at different scales. Spatial is shown to influence landscape pattern analyses, but extrapolation of data across spatial scales may be possible if the grain and extent of the data are specified. The continued development and testing of new methods for spatial-temporal analysis will contribute to a general understanding of landscape dynamics.

Spread of invading organisms

Abstract: D.A. Andow', P.M. Kareiva2, Simon A. Levin3 and Akira Okubo4 'Department of Entomology, University of Minnesota, St. Paul, MN 55108; 2Department of Zoology, University of Washington, Seattle, WA 98195; 3Ecosystems Research Center; Center for Environmental Research; and Section of Ecology and Systematics, Cornell University, Ithaca, N Y 14853; 4Marine Sciences Research Center, State University of New York, Stony Brook, N Y 11794; and Ecosystems Research Center, Cornell University, Ithaca, N Y

Influence of landscape structure on local and regional climate

Abstract: This paper discusses the physical linkage between the surface and the atmosphere, and demonstrates how even slight changes in surface conditions can have a pronounced effect on weather and climate. Observational and modeling evidence are presented to demonstrate the influence of landscape type on the overlying atmospheric conditions. The albedo, and the fractional partitioning of atmospheric turbulent heat flux into sensible and latent fluxes is shown to be particularly important in directly affecting local and regional weather and climate. It is concluded that adequate assessment of global climate and climate change cannot be achieved unless mesoscale landscape characteristics and their changes over time can be accurately determined.

Habitat corridors and the conservation of small mammals in a fragmented forest environment

Abstract: At Naringal in south-western Victoria, Australia, clearing of the original forest environment has created an agricultural landscape dominated by grazed pastures of introduced grasses. Remnant forest vegetation is re-stricted to small patches of less than 100 ha in size, that are loosely linked by narrow forested strips along road reserves and creeks. Six native and two introduced species of small terrestrial mammal (< 2 kg) occur within this environment. The native mammals, being dependent upon forest vegetation, were less tolerant to forest fragmentation than were the introduced species that also persist in farmland and farm buildings. The native mammals displayed an increasing frequency of occurrence in successively larger size-classes of forest patches. Those species with the greatest body-weight were the most vulnerable to habitat loss. All species of small mammal occurred in narrow habitat corridors of forest vegetation on roadsides. The resident status, seasonal variation in relative abundance, patterns of reproduction, and movements of each species were monitored in two habitat corridors during a 25-month trapping study. The corridors were found to facilitate continuity between otherwise-isolated populations of small mammals in this locality in two ways: firstly, by providing a pathway for the dispersal of single animals between patches; and secondly, by enabling gene flow through populations resident within the corridors. The small size of forest remnants at Naringal, and the vulnerability of species with low population sizes, emphasize the importance of preserving a mosaic of numerous habitat patches that together will support regional populations of sufficient size for longer-term persistence. The continuity between remnant habitats that is provided by a network of habitat corridors is an essential, and critical, component of this conservation strategy.

The elements of connectivity where corridor quality is variable

Abstract: Small mammals in heterogeneous environments have been found to disperse along corridors connecting habitat patches. Corridors may have different survivability values depending on their size and the degree of cover they provide.

Modeling vegetation pattern using digital terrain data

Abstract: Using a geographic information system (GIS), digital maps of environmental variables including geology, topography and calculated clear-sky solar radiation, were weighted and overlaid to,predict the distribution of coast live oak (Quercus agrifolia) forest in a 72 km2 region near Lompoc, California. The predicted distribution of oak forest was overlaid on a map of actual oak forest distribution produced from remotely sensed data, and residuals were analyzed to distinguish prediction errors dueto alteration of the vegetation cover from those due to defects of the statistical predictive model and due to cartographic errors. Vegetation pattern in the study area was associated most strongly with geologic substrate. Vegetation pattern was also significantly associated with slope, exposure and calculated monthly solar radiation. The proportion of observed oak forest occurring on predicted oak forest sites was 4O(rlo overall, but varied substantially between substrates and also depended strongly on forest patch size, with a much higher rate of success for larger forest patches. Only 21% of predicted oak forest sites supported oak forest, and proportions of observed vegetation on predicted oak forest sites varied significantly between substrates. The non-random patterns of disagreement between maps of predicted and observed forest indicated additional variables that could be included to improve the predictive model, as well as the possible magnitude of forest loss due to disturbances in different parts of the landscape.

Corridor use by small mammals: field measurement for three experimental types of Peromyscus leucopus

Abstract: Eighteen mice of each of 3 types were radio-tagged and released at 6 standard points in farmland fencerows. Mice were residents (trapped on site) or translocated from distant forest or from distant corn fields. Of total (net) distance moved, most was in fencerows; 77% for residents, 83% for mice translocated from cropland and 92% for mice translocated from forest. Structurally complex fencerows were preferred significantly over intermediate or simple structures by all types of mice. Time spent in movement was not a linear function of distance moved and averaged from 12.5 to 16.5% of total available activity time. Total distance moved in 2 nights averaged 287 to 422 m and area explored averaged 0.67 to 1.15 ha and ranged to 11.0 ha; both exceed literature values for this species in forest. This enlarged scale of landscape use illustrates the potential importance of landscape-specific behaviour. The measurement of rate of corridor use also is discussed.

Structural dynamic of a hedgerow network landscape in Brittany France

Abstract: Changes in agricultural systems since the 50's led to considerable changes in rural hedgerow network landscapes. In these landscapes, ecological processes depend on the spatial structure of the network (length of hedgerows, connectedness, grain size). This paper reports on a study of the dynamics of such a landscape at four periods of time (1952, 1961, 1972, 1985) done on 26 contiguous 16 ha quadrats. A correspondence analysis of the data matrix yields a gradient of change from dense highly connected networks to heterogeneous landscapes with few hedgerows. The study of individual trajectories of the quadrats allowed them to be regrouped in various types of changes. It is possible for a quadrat to go through several pathways. Rates of change varied through time, the 1961–1972 period had most changes. The use of supplementary elements in correspondence analysis proves to be a useful way to approach spatial hierarchy and allows a better understanding of the differentiation of landscape units.

Regional modeling of grassland biogeochemistry using GIS

Abstract: We used an ecosystem coupled to a Geographic Information System (GIS) to simulate spatial variability in storage and fluxes of C and N within grassland ecosystems. The GIS contained information on driving variables required to run the model. These were soil texture, monthly precipitation and monthly minimum and maximum temperatures. We overlayed polygon maps of the above variables to produce a driving variable map of our study region. The final map had 768 polygons in 160 unique classes. The ecosystem model was run to a steady state for each class and NPP, soil organic matter (SOM), net N mineralization and trace gas emission were mapped back into the GIS for display. Variation in all of the above propertiees occurred within the region. NPP was primarily controlled by climate and patterns followed spatial variation in precipitation closely. Soil organic matter, in contrast, was controlled largely by soil texture within this climatic range. Error associated with aggregation within the study area showed that spatial averages over the study area could be used to drive simulations of NPP, which is linearly related to rainfall. More spatial detail had to be preserved for accurate simulation of SOM, which is nonlinearly related to texture. Mechanistic regional models form a valuable link between process studies and global models.

Effects of habitat fragmentation on the red squirrel, Sciurus vulgaris L.

Abstract: The effects of woodlot size and isolation, in relation to habitat fragmentation, on the distribution of the red squirrel were studied. In The Netherlands, 50 woodlots (0.55–13.78 ha) were surveyed in an agricultural landscape for the presence of red squirrel. In 26 woodlots squirrel dreys (nests) were found. Logit regression analysis showed that woodlot size and the area per woodlot covered with coniferous trees were the best predictors of squirrel presence. Addition of isolation variables by means of a stepwise forward regression method showed significant effects of the distance to a large, permanently inhabited wood and the amount of surrounding wood. No effect was found for the distance to the nearest woodlot (>0.5 ha). The model could be further improved by adding a measure of the amount of hedgerows surrounding a woodlot.

The use of a geographic information system to analyze long-term landscape alteration by beaver

Abstract: A Geographic Information System (GIS) was used to analyze how beaver (Castor canadensis) have altered the hydrology and vegetation of Voyageurs National Park, Minnesota over a 46-year period. Maps of beaver ponds prepared from 1940, 1948, 1961, 1972, 1981, and 1986 aerial photographs were analyzed with a rasterbased based GIS to determine impoundment hydrology and vegetation distributions for each map date. Overlay and classification techniques were used to quantify hydrologic and vegetation changes between map dates. The GIS was superior to manual methods for some analyses (e.g., area measurement), and indispensible for others (e.g., transition analysis). Total area impounded increased from 1% to 13% of the landscape between 1940 and 1986, as the beaver population increased from near extirpation to a density of 1 colony/km2. Most of the impoundment area increase occurred during the first two decades, when 77% of cumulative impoundment area was flooded. Once impounded ≥60% of the area maintained the same water depth or vegetation during any decade. GIS procedures were combined with field data to show that available nitrogen stocks nearly tripled between 1940 and 1986 as a result of beaver impoundment.

The spatial pattern of a northern conifer-hardwood landscape

Abstract: A geographic information system, fractal analyses, and statistical methods were used to examine the spatial distributions of old growth hemlock, northern hardwood, mixed hardwood/hemlock stands and wetlands with respect to each other and also soils and topography. Greater than 80% of the stands of any covertype were less than 20 ha in area. Nearly pure hemlock and northern hardwood stands were associated with soils having a fragipan, while mixed hardwood/hemlock stands were associated with sandier soils. Hemlock stands were distributed independently of hardwood and mixed hardwood/hemlock stands, but hardwood and mixed hardwood/hemlock stands were usually surrounded by hemlock. Bogs and lakes were usually surrounded by hemlock stands and are distributed independently of hardwood stands. The shapes of all stands vary from extremely simple to extremely complex, with a general tendency for hemlock stands to be more convoluted than hardwoods. The analyses suggest segregation across soil types and a disturbance regime favoring the establishment of hardwoods and mixed hardwood/hemlock stands in a hemlock matrix as reasons for the origin of the observed spatial patterns.

Analyzing spatial and temporal phenomena using geographical information systems - A review of ecological applications

Abstract: In ecological studies the recent emphasis on larger study areas over longer time spans has coincided with the development of geographical information systems (GIS). GISs are a set of computer hardware and software for analyzing and displaying spatially referenced features (i.e., points, lines, polygons) with non-geographic attributes (i.e., species, age). In the fields of natural resources management and ecology the GIS has been used most frequently for 1) derivation of area or length measures, 2) spatial intersection functions such as file merging, analysis of spatial coincidence and detection of temporal change, 3) proximity analyses, and 4) derivation of data for input in simulation or growth models or calculation of specific metrics. Several current applications of GISs in ecology and natural resources are reviewed.

Continuity and discontinuity of the riparian vegetation along a fluvial corridor

Abstract: The concept of continuity/discontinuity is applied to the riparian vegetation of the corridor of the River Adour (S.W. France), in order to precisely define longitudinal structure, and to test the degree of floristic continuity of the fluvial axis. The measure of floristic connectance along the river course is based on presence/absence data, and is applied to successive stretches of the river, at various resolution levels. This analysis shows that the River Adour corridor cannot be assumed to be floristically continuous. The observed discontinuities may correspond to two types of change in the riparian vegetation: zones of slow change (high level of floristic connectance) or zones of sharp change (low level of floristic connectance).

The fractal shape of riparian forest patches

Abstract: Remnant patches of a forest corridor were examined along the Iowa and Cedar Rivers, Iowa. A fractal dimension was found for these patches which was incorporated with the perimeter:area ratio in an index of shape. This index was then regressed on 5 hydrogeomorphic variables hypothesized to represent processes which might control patch dimensions, plus a variable to represent human impact. The hydrogeomorphic variables were derived from topographic maps; the impact variable used was the proportion of perimeter that was occupied by a road, railroad, transmission line, urban or other built area, or a straight line judged to be agricultural. Three variables remained significant in a reduced model: human impact, valley width, and stream sinuosity, but together the three accounted for only 24% of the variance in patch shape. The fractal perimeter:area ratio increased with human impact, probably because of reduced area, and decreased with valley width, which allowed more extensive forest on wide floodplains, and with sinuosity, which resulted in small patches isolated on the interior of meanders. These results indicate that in this landscape the hydrogeomorphic structures play a role, but that human impact is more significant in its effect on the shape of remnant forest patches. Other structures, such as the regional topography, may account for the unexplained variance. The index of shape used here may be useful as an independent variable in studies of ecological processes affected by patch shape and form and as a guide to conservation.

Influence of a shrub corridor on movements of passerine birds to a lake littoral zone

Abstract: A pine forest was separated from a lake littoral zone by a meadow on one area (discontinuous) while these habitats were separated by a shrub strip in another area (continuous). This shrub strip acted as an ecological corridor enhancing the movements of birds between the forest and the littoral reed zone. The number of individuals of non-littoral species that visited the reed zone was higher (p < .001) on the area with the connecting shrub strip in autumn but the number of species visiting the littoral zone was not significantly higher. Significantly more (p < .001) autumn movements by birds in the continuous area were oriented along paths between the forest and the littoral zone whereas movements in the discontinuous area paralleled the littoral and forest zones (p < .001). Movements of birds were concentrated along the edge of the shrub strip. The spatial configuration of the landscape facilitated access by some forest birds to the littoral habitat.

Home range: A fractal approach

Abstract: Most current methods for describing animal home range assume that it may be represented as a Euclidean type shape such as a bell shaped curve or a closed polygon. Landscape ecology has increasingly shown that ecological objects are more often highly fragmented and irregular. A fractal approach to description of animal home range was thus developed. For each point where the animal was observed, a circle centered on this point was first laid down to represent the area searched for prey by the animal during a short time interval. In this way the behavior of the animal and differences between species can be represented. Next, a fine grid is laid over the map and the height of each grid square computed by the number of circles that overlap that square. Then, the fractal dimension of the resultant 3-D surface is calculated at several scales. From an analysis of data from a hawk, the existence of perching behavior can be inferred, as well as the observation that at coarse scales the hawk behavior is self-similar and resembles a random walk. The home range thus analyzed in no way resembles a closed figure such as a polygon because it is highly fragmented. Further analysis showed that the fractal measures are relatively insensitive to sample size and to measurement error. Code is included for performing the analyses.

The complex relationship between landscape and recreation

Abstract: The relation between landscape and recreation is very complex. There are various, interrelated approaches to analyze this relation, such as land evaluation, impact analysis, spatial behaviour analysis, and assessment of the scenic quality of the landscape or landscape evaluation. In many of these approaches airphoto interpretation can be a useful tool.

Dependency of local mesotrophic fens on a regional groundwater flow system in a poldered river plain in the Netherlands

Abstract: The effect of regional, subregional and local groundwater flow systems on mesotrophic fen ecosystems was studied in the polders of the Vecht River plain that borders the Pleistocene ice-pushed moraine of Het Gooi. Variation in the vegetation and in the habitat factors (groundwater and peat soil) of fens depends whether or not the fens are connected to the outflow of the regional groundwater system. Changes in the regional groundwater flow system, caused by changes in the water management of the polders, are probably responsible for the deterioration of mesotrophic fens. Drastic measures will have to be taken to restore the hydrology on a regional scale if the mesotrophic fens are to be saved from extinction. Hydrological research that integrates the results of regional and local studies is essential if the ecology of fen ecosystems is to be understood.

A polygon-based spatial (PBS) model for simulating landscape change

Abstract: A spatial model of long term habitat succession at a degrading Louisiana wetland was constructed based upon simulating exchanges across irregularly shaped polygons. Polygons represented the natural morphology which is indicative of the natural landscape. The PBS model was partially successful in simulating spatial habitat changes over a 28-year period when more than 1000 ha of wetland loss occurred (r2=.56). General landscape trends did, however, emerge from the model development. Areas of high annual water level fluctuations, and high primary productivity were less likely to change from wetlands to open water and were most likely to recover if altered. We discuss the potential for predictive improvement and for integration with polygon-based geographic information systems, and conclude that a PBS model demonstrates the need for spatially explicit landscape management.

Landscape, law and public policy: conditions for an ecological perspective

Abstract: Within the conditions inherent in nature, human communities tend to live in the kind of environment that they have made for themselves. All may not be happy with their surroundings, but the values and attitudes of the collective community ultimately determine what the quality of those surroundings will be. Having over the years directly experienced ugly and impoverished settlements in both the so-called developed and less developed worlds, I am persuaded that their inhabitants are more ready to accept degraded surroundings than to mobilize their latent resources to build better environments. Unhappily, even when they are motivated, those resources are often deficient in ecological insight and information. The visual chaos of most American cities reflects the priority of rugged individualism in the pursuit of return on capital investment. Similarly, the degrading of the countryside and rural landscape by visual clutter expresses the tacit preference of perhaps most Americans for the rights o f land owners and entrepreneurs to create jobs and profits when and where opportunity is present. In Europe rings of multistoried appartment houses, without adequate service and recreational facilities, around the central city illustrate a different, but equally serious, problem of design and planning. And, the barrios and slums associated with large cities in developing countries also demonstrate the failure of public authorities and the lack of political will to create viable landscapes and cityscapes. However, my personal experience, and my remarks, are derived from the American experience with such issues. The values and assumptions of a people are ultimately written into their laws and political priorities. Values and assumptions institutionalized in statutes and judicial precedents change more slowly than do societal circumstances; institutional inertia preserves rights and privileges that in many places would no longer be acceptable if the law were being written de nova today. In America the attitudes of the frontier have been preserved and passed on to generations for whom their assumptions are inappropriate and their implications ecologically and aesthetically harmful. For many Americans the coonskin cap remains an obsolete symbol of environmental values. As John Ise explained, Americans, as a result of their historical conditioning, \"a re land value animals.\

The long-term influence of past land use on the Walker Branch forest

Abstract: Forest structure and composition influence patterns of insect outbreaks and can be explained on the Walker Branch watershed by past land use (timber harvest and agriculture), soils, aspect, and slope. In particular, pine bark beetles caused large losses of pine on sites that had been used for agriculture, on Fullerton silt loam soils, and on north-to-northeast and east-to-southeast exposures. Hickory bark beetles had a high impact on hickory biomass on Bodine soil areas that were forested in 1935 and sloped greater than 11%. Thus, prior land use can have an indirect effect on future disturbances.

Nature and origin of stone stripes on the Columbia Plateau

Abstract: Beds of size-sorted stones forming stripes perpendicular to the contour are conspicuous on hillsides of the Columbia Plateau. Stripes occur on terrain ranging from 0° to about 30° in steepness, often beginning among Mima-type mounds on mesa tops and extending downward onto steep, unmounded slopes. Four mechanisms of their origin have been hypothesized: 1) water erosion, 2) solifluction and soil creep, 3) weathering of rock outcrops, and 4) tunneling by pocket gophers. We measured characteristics of five stripes on slopes of differing exposure and steepness. These stripes were 58–124 m long, and widths showed a maximum range of 0.55–3.70 m. Data on physical and biotic characteristics of the stripes suggest that pocket gopher tunneling is a basic mechanism of stripe formation on gentle slopes, and that this mechanism is augmented by outcrop weathering and colluvial dynamics on steeper slopes, with erosion playing a secondary role.

Historical land use and hydrology. A case study from eastern Noord-Brabant

Abstract: The historical geography of the landscape of a lowland brook valley in the sandy Kempen area (eastern Brabant, Netherlands) shows the interaction of ecological processes and land use, and helps to understand processes in the present landscape. In this location the human influence, especially on the groundwater hydrology, played a major role in the development of the landscape. Levels and flow of different types of groundwater interacted with vegetation development and human interference, to produce landscape patterns. Four main stages have been identified. In the prehistoric period, a natural deciduous forest covered the higher grounds, ombrotrophic peat was formed in the valley, and groundwater was relatively deep. In the medieval stage man settled on the edge of the valley, cleared parts of the forest and dug part of the peat. Groundwater levels were raised, which increased the rate of groundwater discharge and increased the amount of associated lowland peat formation in the valley. This tendency continued in modern times, when the area was completely deforested. Groundwater levels increased further due to decreased evapotranspiration, which gave rise to the use of ponds for fish and for water mills. Finally, in the most recent period the groundwater level has been lowered by extensive artificial drainage, partly on a regional scale. It was concluded that evaluation of historical changes in the landscape help provide landscape planners with a sound idea of the nature of the landscape.

GIS: More than just a pretty face

Abstract: Most landscape ecologists have heard about Geographic Informat ion Systems (G1S), and many are in the process of acquiring a GIS, but there is still an aura of mystery, skepticism, and misconception about what a GIS is and what it can do. Some people have adopted an ' E m p e r o r ' s New Clothes ' stance on GIS, perceiving it as just another elaborate (and expensive) way to draw pretty maps. A GIS ' s graphic display capability is certainly one of its most aesthetic properties, so it is not surprising that talks illustrating GIS use are often peppered with attractive, colorful slides. But GIS is more than just a pretty face. Its power for landscape ecology lies in its ability to manipulate and analyze spatially distributed data. While communi ty and ecosystem ecology has traditionally focused on the central tendency of observations made at carefully selected points in space, landscape ecology focuses on the heterogeneous distribution of ecological resources, populations, and processes over space and time. The GIS ' s spatial and temporal analysis capabilities therefore make it an indispensible tool for landscape ecology research. The types of questions typically addressed are: