Urban Ecosystems, 1997, 1, 201–216
Methods for spatial and temporal land use and land
cover assessment for urban ecosystems and application in
the greater Baltimore-Chesapeake region
TIMOTHY W. FORESMAN*
Department of Geography, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
STEWARD T. A. PICKETT
Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA
WAYNE C. ZIPPERER
USDA Forest Service, 1100 Irving Avenue, Syracuse, NY 13210, USA
Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that
can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods:
(1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban
ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the
geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This
information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to
evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census
data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A
geographic information system (GIS) integrates core analyses with historic data on land use change to yield a
comprehensive land use and land cover framework and rates of change. These data resources establish the regional
foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and
patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological
and social patterns and processes for varying degrees of urbanization.
Keywords: land use; land cover; urbanization; urban-rural gradient; paleoecology; GIS; historical mapping; Baltimore-Chesapeake region; history
Introduction
An understanding of processes that cause the shifting mosaic of land cover in regions should be based
on fundamental knowledge of the physical environment’s influence on vegetative communities as well
as human impact on the landscape. The incorporation of physical and human factors is especially
important for environmental or ecosystem analysis in urbanizing and urban landscapes. Human impact
has become a major determinant for land cover through the various modifying activities associated with
land use.
In attempting to understand these relationships, scientists and decision makers often rely upon classification systems to document or map the spatial extent of land cover, land use, or a combination of land
* To whom correspondence should be addressed.
1083-8155 © 1997 Chapman & Hall
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cover and land use. Comprehensive analyses of land cover and the influence of land use on environmental
services for water, soil, air, and biodiversity, often require combining land cover and land use parameters.
The United States Geological Survey (USGS) Anderson et al. (1976) classification is a prime example
of a recognized national land use/land cover classification system. However, this combination is not as
simple or straightforward as the existence and extensive use of land cover/land use maps and classification systems might lead an observer to believe (Loveland et al., 1991; Westmoreland and Stow, 1992).
Separating land use and land cover data in initial stages of the analysis provides an improved basis for
connecting socioeconomic, physical, and ecological data on urban areas. This paper seeks to: (1) critique
the combination of land use and land cover; (2) evaluate three methods that can be used to assess past
and on-going land transformations; and (3) show how these methods are used to construct a temporal
model of land transformation in the Baltimore-Washington region. The three methods are core analysis,
historic mapping, and gradient analysis.
Land cover distributions, the biophysical skin of the earth’s surface, are based on biogeographic
variations in the climate, topography, and edaphic factors. Land use distributions, the status of human
operations on the earth’s surface, represent the arrangement of human activities based on land ownership,
zoning policy, and management practices. Therefore, land cover/land use maps present an explicit
compromise with the inferred ability to conduct analyses on either land cover or land use. The incorporation of these two distinct land surface phenomena for input into ecological processes studies or
models requires appropriate scientific metrics. We offer the concept that landscape ecology studies
should not rely on the aggregation of land cover and land use variables, especially for human dominated
landscapes along urban-rural gradients (McDonnell and Pickett, 1990). Instead, we suggest that these
variables should be collected and maintained as separate and distinct landscape parameters.
Ambiguity of urban landscape terms and definitions for the gradient continue to plague both the
science and policy communities (Ratcliffe, 1997, pers. comm.). Our use of the term ‘‘urban to rural
gradient’’ (often simply urban-rural) encompasses the landscape zones recognized by such terms as
central business district, suburban, urban extent, urban fringe, or city edge. We view this zone as a
gradient ranging spatially from the central city to the hinterlands of farms and forests. From an ecological
perspective, the zone represents functional differences in transitional patches between city and country
(McDonnell and Pickett, 1990; Pouyat et al., 1994). The gradient need not be a literal linear transect from
urban to rural, but is used to conceptually order the impacts of urbanization as one moves from urban to
rural. Our use of the term ‘‘framework’’ encompasses the conceptual setting of a study including
database resources that provide spatial and/or temporal organization of a specific investigation’s context.
The ability to provide accurate and appropriately scaled land cover and land use data sets is essential
to investigate the many possible functional relationships and pathways for the human activities interacting with ecological processes (Pickett et al., 1997). Yet, a scheme for a universally accepted land cover
or land use classification does not exist. Furthermore, the variety of schemes used to define global
vegetation are remarkably disparate (Estes and Mooneyhan, 1994). Likewise, plant ecologists traditionally have not incorporated human-induced factors as components for vegetation classification or mapping
(Mueller-Dombois and Ellenberg, 1974).
Human factors, however, are increasingly being recognized as the driving force behind the rates and
trajectory of change upon the earth’s surface (Likens, 1991; Vitousek, 1994; Turner and Meyer, 1994).
Global change researchers, however, have not been able to access appropriately scaled information to
incorporate this complex mosaic of land cover and land use variables in their modeling schemes. An
understanding of the trajectories of these driving forces requires a temporal perspective. Both paleoecological and historical land cover and land use maps are considered important to establishing the temporal
perspective or framework of landscape dynamics for ecological studies (Brush, 1989). Defining historic
trends along the conceptual urban-rural gradient is considered necessary for evaluating various impacts
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from past land transformations, testing temporal relationships discovered in space (Pickett et al., 1997),
and attempting to predict potential future modifications in human dominated ecosystems.
Assessment and mapping methods
This paper explores three complementary methods—paleoecological, historical, and contemporary—
being used by the authors to construct temporally and spatially explicit land cover and land use databases
in the context of long-term ecological studies within the Chesapeake Bay watershed. Whereas the
objective for using these complementary methods is to provide a quantitative framework within which
detailed urban-rural ecological gradient studies can be performed, the methods are appropriate for any
environmental setting. Landscape processes are ineluctably connected to the functional relationships of
land ownership, economic prerogatives for resource exploitation, and human social or political influences
(Forman, 1995). Studies directed at assessing environmental change or at delineating impacts from
natural and human processes, depend upon a thorough foundation detailing the system’s long-term
ecological behavior as well as the specific causal agents of human-induced inputs. Fundamental knowledge of the processes and interrelationships of the physical, ecological, and social components on the
urban-rural gradient are poorly understood (McDonnell and Pickett, 1990). As recognition of the importance of studying urban ecosystems increases, the concomitant requirement to provide historical and
paleoecological frameworks for these studies will also increase.
Urban-rural gradient. Ecosystem studies need to understand human influences on ecological processes
(McDonnell and Pickett, 1990; Pickett and Cadenasso, 1995). Urban ecosystems represent the most
complex mosaic of vegetative land cover and multiple land uses of any landscape. Ecologists, seeking to
understand the numerous pathways for successional states in land development relative to the vegetative
structures and impacts of these structures on biodiversity, recognize the need to better understand this
complex gradient (Pickett et al., 1987; Soule and Kohm, 1989; Zipperer, 1993). Recent investigations
have unveiled striking features of ecosystem processes along a gradient of urbanization (McDonnell et
al., 1997). Functional differences include N-mineralization rates, decomposition rates, and carbon cycling (Pouyat et al., 1994; McDonnell and Pickett, 1990). These findings suggest that detailed analyses
of land use histories are required to understand patterns of urban vegetation, i.e. forest patches, and
ecological processes along an urban-rural gradient (Sharpe et al., 1986; Zipperer, 1993).
An urban-rural gradient approach also improves our understanding of how human actions affect
hydrologic processes and biodiversity. For example, hydrologic models of the urbanized areas that
traditionally relied on percent canopy cover to characterize urban landscapes. Because of increased
spatial resolution of the data, modelers are now investigating the influence of spatially explicit land cover
and land use parameters on hydrologic processes (Band and Moore, 1995; Green and Cruise, 1995).
Fauna also are being more intensely studied because of concerns for both biodiversity and assessment of
disease vectors in urban landscapes, e.g. Lyme disease (Soule and Kohm, 1989; Stoms et al., 1992).
Spatial analysis. Spatial analysis tools (e.g. geographic information systems and remote sensing) for
acquiring, storing, and analyzing land cover and land use data can be successfully used to create regional
frameworks for interdisciplinary studies in urban ecosystems (Skole, 1994; Cowen et al., 1995). Knowledge of where land conversions occur and the spatial characteristics associated with these conversions are
required to define the specific pathways and processes of change operating within urban ecosystems.
Long-term ecological assessments need to build the groundwork for baseline, historical trends on land
cover and land use patterns and provide insights to questions of rates of change for flora, fauna, nutrient
fluxes, and human impacts. In addition, land cover changes must be assessed at different scales in order
to expose the different social, ecological, and physical drivers and constraints that may operate over the
range of spatial scales.
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Paleoecological methods for land cover
Sediment cores from the Chesapeake Bay estuary and its tributaries have been essential in documenting
the land use effects of deforestation, agricultural expansion and intensification, and urban sprawl in the
watershed. Brush (1994) has compiled a substantial set of sediment cores, complete with biological
indicators, to reconstruct the land cover conditions around the Chesapeake Bay estuary before European
settlement (Fig. 1). The sediment record portrays composite profiles of the areal extent of land cleared,
along with sedimentation rates, ragweed dating profiles, planktonic diatom species, and submerged
aquatic vegetation. These assemblages provide evidence of the land cover dynamics during the past few
centuries, thereby providing an ecological trajectory for further assessment of contemporary urbanization
impacts.
Careful analyses of the vertical increments of core samples were used to estimate estuarine sedimentation rates for the past 11 000 years (Brush, 1989; Cooper and Brush, 1991). The paleoecological record
preserved in sediment cores provided critical evidence for comparing effects of human activities with the
effects of climate change in the past with an eye to the future. In the Chesapeake Bay region, ragweed
(Ambrosia sp.), a prolific pollen producer, colonized areas of disturbed soil and, therefore, produced a
distinct horizon related to large scale land clearance from agricultural activities. Another distinct horizon
in this region was derived from the demise of the American chestnut in the late 1920s, when the
disappearance of chestnut pollen demarked the stratigraphic record. With adjusted sedimentation rates,
actual calendar years were assigned to the samples (Brush, 1989). Reconstruction of the biological
populations for land cover and estuarine ecosystems were calibrated with the dated samples. Changes in
fossilized indicators within cores were related to historically documented land use and compared to the
Figure 1. Paleoecological analysis of the upper Chesapeake Bay as determined from sediment core analysis (reprinted with permission from Brush, G. S., 1994).
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prehistoric chronology for a more complete understanding of conditions before and after human settlement impacts.
Integrating paleoecology and history: a picture of today and projections for tomorrow
Historical trends of land cover and land use impacts can be investigated using the convergent and
complementary tools of paleoecological chronology, historical land use records, and modern vegetation
mapping. For urban landscapes, these historical contexts, with the attendant data types for land and
estuary biota present time-series data to better calibrate, with precision, the rates and patterns of urbanizing landscape parameters. Brush (1994) and Yuan (1995) have used cores to document the major
settlement periods and land use trends impacting the ecological conditions for the Chesapeake Bay region
(Table 1). Spruce and fir characterized the postglacial period dominating the Chesapeake Bay landscape
for approximately 3000 to 4000 years. This was followed by hemlock. As the climate warmed, the region
experienced less precipitation, providing conditions for a closed-canopy forest of oak-hickory to dominate the landscape. The paleoecological record indicates that these conditions, which began about 5000
years ago, continued up to European settlement in the 17th century when ragweed pollen provides
evidence that approximately 20% was cleared for agriculture. Sedimentation rates display significant
increases when land clearance exceeded 20% (Brush, 1989). During the next 100 years, agricultural
expansion on small farms for grain and tobacco resulted in additional land clearing of up to 40%.
Deforestation for farming was augmented in many areas by timber cutting for energy demands of the iron
furnace industry (Travers, 1990; Brush, 1997). With the advent of guano-based fertilizers and the
industrial revolution, the last half of the 19th century experienced 60 to 80% land clearance for agriculture. The 20th century saw continued land cover transformation, including drained wetlands and urban
sprawl continuing in classic patterns of development (Von Eckardt and Gottman, 1964) around the
Baltimore region. With farm abandonment, forests began to regenerate on previously cultivated land.
Post World War II saw an expansion of urban land use significantly altering and impacting the region’s
Table 1. Land use and land cover historical trends for the Chesapeake region
Time frane
Period
Land use/land cover characterization
10 000–5000 B.C.
Pre-human
5000 B.C.–1600 A.D.
Pre-European
1600–1750
1750–1850
Early settlement
Colonial towns to rural
agrarian intensification
1850–1900
Agricultural transition to
industrialization
1900–1950
Modern urbanism and
industrialization
Modern transportation,
population growth and
urban sprawl
Boreal type forest succeeded by hemlock into
enclosed canopy mixed conifers-deciduous
forest.
Oak-hickory, closed canopy forest dominates
landscape except for tidal wetlands and
serpentine barrens, frequent fires.
20–30% land cleared for tobacco farming.
40% of land cleared, grain and tobacco farming
on small farms, deforestation for iron
furnaces and construction.
60–80% of land cleared for large farms,
introduction of deep plough and guano-based
fertilization.
Chemical-based fertilizer, extension of farms
and urban with wetland drainage.
Decrease in cultivated land, forest, i.e.
generating, urban expansion.
1950–Present
(Modified from Brush, 1994)
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ecosystems. The effect of this urban sprawl is only recently being quantified and set into a conceptual
framework for assessing the ongoing rates of change in ecological processes and the various trajectories
for the ecological system components (Pickett et al., 1997).
Historical land cover assessments
Assessing the trajectories of land cover in areas impacted by rapid urbanization requires a series of
accurate land cover maps. A baseline or ‘‘natural’’ vegetation is needed to assess historical changes in
spatial and structural composition and to project expected vegetation patterns into the future. Whereas
numerous vegetative maps have been generated for the Chesapeake region (Brush et al., 1980; Dobson
et al., 1995; USGS, 1996), the lack of ground sampling and verification protocols restricts the application
of such vegetation maps for quantitative floristic determination. For example, most of the vegetation
classifications based on satellite images display only gross aggregates of vegetative land cover classes
(Henderson-Sellers et al., 1986). As ecologists’ interest lies in how one species or plant association will
succeed another, given a pattern of disturbance that is either climatic, stochastic (i.e. fire), or anthropogenic, these coarse scale categories of vegetation patterns may not satisfy ecosystem-level analyses in
urban areas.
Within the Chesapeake region, landscape-level vegetation maps did not exist until recently. Besley
(1916), Stetson (1956), and others provided descriptions of forests existing at the time of European
settlement. This information can be augmented by witness tree records listing species at known locations
from the late 1600s to the early 1700s. At the turn of the century, Forrest Shreve and associates (1910)
provided an excellent survey of Maryland’s flora by identifying both herbaceous and tree species on
different soil types. Also, for certain urban parks, descriptions of the forest species can be found in
historical documents.
With the Chesapeake region, however, a definitive delineation of the natural forests of Maryland was
not performed until the mid 1970s (Brush et al., 1980). Brush and associates (1980) defined the Maryland
natural forests as those regenerating naturally under a variety of disturbance patterns. The forests were
differentiated, without attention to age classes, into 18 associations and mapped at a scale of 1:250 000.
The original map was produced with a minimal mapping unit of two hectares (Fig. 2). Maryland’s forests
were mapped by recording all species present, irrespective of size, and generating polygonal boundaries
around all areas of homogeneous species composition recognized in the field by indicator species. These
mapped associations include different stages and origins of forest growth, e.g. recently cut-over areas,
reforested abandoned farmland, remnant forests undisturbed for more than 100 years, and hedgerows.
The 18 forest associations were found to be related closely to patterns of available water, regardless
of the topographic and geologic differences separating the physiographic provinces (Brush et al., 1980).
Lithologically different substrates are often similar hydrologically. A good example is the chestnut
oak-post oak-blackjack oak association that occupies several different substrates with common hydrologic characteristics. This same association was identified on fragipan, gravel, and serpentine, which
differ texturally and chemically but are hydrologically similar (Brush et al., 1980). Where humaninduced hydrological alterations have occurred, shifts in association distribution have resulted. According
to Brush et al. (1980), current land use has had little influence on existing forest patterns. Except for
activities such as road building and construction that can change drainage patterns, correlations between
the forest associations and substrate units were found to remain generally consistent. These findings and
the forest map provide a spatial framework or ecological reference point to investigate historical land
cover trajectories.
Contemporary land cover assessments and mapping
Advanced tools for spatial analysis, i.e. remote sensing and GIS, represent important technologies for
providing local, regional, and global histories (Acevedo et al., 1996; Skole and Tucker, 1993; Brondizio
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Figure 2. Maryland’s Natural Forests Map Displaying Thirteen of Eighteen Forest Associations (recreated from
Brush et al 1980).
et al., 1996). First, remote sensing enables quantitative measurement of the earth’s surface biophysical
properties, with a legacy of more than 50 years of aerial photography for many portions of the globe and
about 25 years for global satellite coverage. Remote sensing offers plant ecologists and soil scientists, as
well as others tasked with mapping the earth’s surface phenomena, both a medium for recording the
spatial distribution of features of interest and data for analyzing the reasons for these distributions.
Limitations of remote sensing, that is, the inherent resolution for discriminating cover types relative to
the minimum mapping unit for the investigation, can be addressed primarily by field verification. Field
verification, however, imposes a labor cost that invariably restricts the geographic extent of detailed
mapping surveys. In addition, national standards do not exist for performing verifications, but rather
conventions exist for vegetation or soil sampling that are derived from ‘‘schools’’ of experience. A
survey of field technique texts or manuals will substantiate this finding (Loundsbury and Aldrich, 1986;
Csuros, 1994). Lack of verification standards results in significant disparity in the accuracy of land cover
maps from remotely sensed data. A rigorous approach to verification issues was demonstrated by Coastal
Change Analysis Program (CCAP) along the east coast (Dobson et al., 1995). This project relied upon
both labor-intensive methods and the use of regional experts to generate highly accurate, and tested, land
cover classifications from Landsat Thematic Mapper and aerial photography. Although the classification
scheme adopted the use of a combined land use/land cover approach, the methods for verification are
scientifically defensible. In addition, CCAP classification provides a GIS format that is optimal for
managing land cover data in a digital form (Dobson et al., 1995).
Historical land use mapping
Paleoecological analysis that generates land cover chronologies presents extremely valuable data for
local and regional ecosystem studies. By itself, however, the paleoecological analysis does not provide
the spatial precision necessary to reconstruct a farm-by-farm, neighborhood-by-neighborhood assessment
of past and present land use (Brondizio et al., 1996). Quantitative, historical land use information can be
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effectively reconstructed through the careful compilation of complementary sets of tabular, census, and
mapping data sources. This approach was used in the San Francisco Bay area (Kirtland et al., 1994) and
the Baltimore-Washington area (Acevedo et al., 1996; Foresman et al., 1996).
The Baltimore-Washington project compiled historic maps, demographic data, environmental parameters, and satellite images to map human-induced land transformations from 1792 to 1992 for the
Baltimore-Washington region (Fig. 3). All data were reformatted to a common spatial reference using a
GIS. This figure portrays the dramatic increase in urban expansion and population growth experienced
during the past two centuries. With more than 7 million people in the greater Baltimore-Washington
region, the study site captures one of the nation’s fastest growing examples of urbanization spreading into
wetland, forested, and agricultural ecosystems (Foresman et al., 1996). The increasing occurrence of the
megalopolis formation has been highlighted by urban geographers concerned about the relationships of
both social and environmental ills associated with urban decay (Von Eckardt and Gottman, 1964).
Land use compilation for the urban extent and the transportation categories was accomplished with a
combination of techniques including manual map transcriptions, table digitizing, and digital image
processing of the satellite data. The exact compilation procedure depended upon the condition and areal
extent of the source materials. A set of criteria for urban extent was established based on comparing
settlement patterns from map or satellite sources and cross referencing the locational information with
census data. An urban center, or town, was registered when a population of 500 persons was reached.
Census data were used to track the numbers and characteristics of the population back to the 1790 census
nationally, and before 1790, depending on the county or incorporated area records. Using standardized
data allows the use of this technique for much of the American urbanized landscapes.
Figure 3. Two-hundred years of urban growth for the Baltimore-Washington region.
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Two hundred years of urbanized growth
The eight images displayed in Figure 3 illustrate urban growth in the greater Baltimore-Washington area
from 1792 to 1992. This region covers a 2-degree latitude by 2-degree longitude area for much of
Maryland, the northern portion of Virginia, parts of West Virginia and Pennsylvania, and the District of
Columbia.
After a century and half of colonial settlement, an urban pattern began to occur around the ports such
as Annapolis, Baltimore, and Alexandria as the primary focal points for development. Located on the fall
line between the Coastal Plain and the Piedmont Plateau, the towns became important trade centers for
the plantation-based economy, driven by the cultivation of tobacco, grain, and livestock.
By the 1850s, Baltimore became an expanding urban and industrial center with the bulk of the 1
million people in the region residing in Baltimore City. The Baltimore and Ohio Railroad connected
Baltimore and the Midwest. In contrast, Washington remained a relatively small city. A network of rural
cities began to develop in the hinterlands of Baltimore, whereas many colonial era ports throughout
Maryland and Virginia became inaccessible for shipping because of heavy siltation, a result of deforestation and overuse of agricultural fields.
At the turn of the 20th century, two million people in the region began to form the suburban
environment with the advent of street cars and extensions of rail lines. Half of Maryland’s population
resided in Baltimore with western towns growing along the rail line. Suburban sites continued to grow
and by 1925, the ‘‘inter-urban’’ rail lines allowed commuter villages to become towns. This growth
resulted from the economic prosperity of an increasingly industrialized Baltimore City.
At the half century mark, significant filling of suburban areas adjacent to the central cities was
augmented by the additional growth of urban areas made possible by the advent of the automobile and
improved transportation infrastructure. Growth of the federal government in the 1930s and 1940s spurred
growth around Washington and the adjacent counties. By 1972 and continuing to the last two frames of
1982 and 1992, the urban growth connected the corridor between Baltimore and Washington. Rampant
growth and urban flight continue to change the land use in the area from agriculture and forest to urban.
By 1992, more than 8 million people resided in the study area at an average density of 466 persons per
square mile (Ratcliffe, 1997, pers. comm.).
Visualization methods
Once a historical land use database is compiled, the data can be applied to other investigations. As digital
data, the historical land use structure can be used to evaluate the impact of the land use on land cover
dynamics. One approach is to visualize data from different perspectives. Masuoka and associates (1995)
generated an oak-hickory forest closed canopy image for the Baltimore region by draping the spectral
signature for forest canopy, as derived from Landsat TM data, over a digital elevation model for the
region (Fig. 4). The resulting depiction provided a perspective of Baltimore much as it would have looked
before European settlement. The classification of urban land use was then projected over this historically
accurate view of the landscape for the 200-year period. Through visualization, it is apparent that the
agriculture land use classifications were missing from the image. These projections provided an artificial,
bimodal perspective for forested and urban categories that represent a mix of land cover and land use.
The combination of these classification conventions visualized for the landscape represents land cover
and land use classification’s dual nature as a foundation for ecological studies. Significant enhancements
through the creation of additional data to the database are needed to correct the duality, and provide a
more spatially accurate definition of historical land transformations and conversions for the land surface
characteristics.
The methods for creating historical land use databases are appropriate for most of the North American
continent in terms of defining processes of land transition and urban landscape dynamics, as well as other
environments, for example, the tropics (Brondizio et al., 1996; Skole and Tucker, 1993; Tucker et al.,
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Figure 4. Baltimore area prospective of two-hundred years of urban growth on forested background.
1985). By using national data assets that are relatively easy to combine with digital databases from the
National Spatial Data Infrastructure (NSDI), we envisage the construction of a national set of historical
databases (NSDI, 1994). The potential for producing this set of databases over the next decade is quite
reasonable considering the interest by federal agencies to build upon San Francisco and BaltimoreWashington historical mapping experiences. The potential for cooperative development of one kilometer
land cover and land use databases for whole continents is also feasible by adopting similar NSDI
structures for the globe (Tucker et al., 1985; Loveland et al., 1991; Earthmap, 1995).
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Contemporary land use assessment and mapping
Contemporary land use assessment and mapping can be accomplished in part with the same tools and
methods described in the ‘‘Contemporary Land Cover’’ section. However, the critical difference lies in
the inability to determine from remotely sensed resources (aircraft or satellite) the ownership of the land,
the ownership practices on the land, and policies controlling land management activities. Obtaining these
key land management variables for extensive areas of the landscape requires significant investigative
resources. For urban areas, obtaining land use information requires access to parcel-level records of deeds
and zoning typically located at county recorder’s and assessor’s offices. Only recently has the existence
of digital files from these offices become a viable data source for investigators. Previous research efforts
required painstaking data collection from county offices and then conversion to digital formats for
analysis. Outside the urban areas, access to land use data for agriculture can be obtained through the
Natural Resource Inventory of the Natural Resource Conservation Service (NRCS, 1996). However,
some level of confidentiality is retained, thus limiting data access. Other records are culled from various
federal and state offices. With federal, state, and local agencies modernizing their land management
records in GIS compatible formats, the ability to generate accurate and verifiable land use maps and
conduct assessments on land use impacts will improve dramatically.
Discussion: generalizing the approach
The urban-rural gradient is a conceptual tool to permit the comparison of pattern and process of systems
over wide areas and has been recommended to the ecological community as a means of addressing
significant gaps in our knowledge of the urban landscape (McDonnell and Pickett, 1990; Allen and
Hoekstra, 1992). An approach based on differences along a gradient can be applied to a wide range of
geographically disparate landscapes experiencing urbanization. A principal benefit of a gradient approach
derives from the advanced level of understanding of gradients from different active disciplines, i.e.
ecological (McDonnell and Pickett, 1990), social (Grove, 1996), and hydrological (Band and Moore,
1995). A second key approach to urban ecosystems is the use of patch analyses to define vegetation and
social patterns. Hydrological or physical processes can also be linked to changes in patch configuration.
The patch approach complements the gradient approach because it is spatially explicit and can be used
hierarchically to discover the scales at which certain patterns and processes operate. Ecological, social,
and hydrological fluxes can occur among patches. Integrative modeling of ecological, social, and physical variables when linked or defined as patches, can be used to identify the functional interactions of these
variables (Pickett et al., 1994).
The suggestion that both gradient analysis and patch analysis are effective approaches toward integrating ecological, social, and physical variables of an urban landscape is based on the depth of theoretical understanding for these approaches in the different disciplines. From the ecosystems perspective,
we are concerned with the relationships between structure, species composition, and the arrangement of
land cover patches, from the urban core to the rural hinterlands, plus how these relationships influence
the function of hydrological processes. To reach an advanced state of integration amongst ecological,
social, and physical variables requires keeping the land cover and land use parameters separate.
Beyond our concern for spatial arrangements of the urban ecosystem in our field studies lies a concern
for its temporal arrangements. Whereas alternative modeling designs can incorporate temporal data sets
into ecosystem models (Farmer and Rycoft, 1991), these efforts are limited to time slices of land cover
and land use data. Peuquet (1994) has offered a conceptual framework for pursuing various avenues for
time series analysis. However, little progress has been made outside the inherent approach of using time
slices for modeling input and analysis (Foresman et al., 1996).
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Paleoecological records of indicator organisms and materials derived from estuarine sediment have
proven valuable for reconstructing the history and prehistory of the urban watersheds. Analysis of
sediment cores for pollen, preserved diatoms, and remains of other organisms, when calibrated by carbon
dating, generates important evidence of land cover patterns and relationships between land use and
estuarine ecosystems. This evidence provides a chronology for defining regional vegetation community
dynamics. Although there are relatively few local or regional sediment analyses, the importance of the
existing data points for temporal and spatial calibration, and assessment of human-induced land transformations cannot be overstated. Investigations of the role humans have played in the Chesapeake Bay
watershed and estuary have demonstrated the significance of human-induced alteration from the states of
postglacial ecosystems to the present configuration. With paleoecological studies, Brush (1994, 1997) has
documented radical landscape transformations of land cover and land use in the watershed. These
transformations not only had profound negative impacts on the diversity of estuary biota but also
influenced water quality and quantity. Although historic land cover and land use analysis can provide
important understanding regarding the rates of change for major landscape elements, paleoecological
records are necessary to establish the long-term performance of ecosystems in response to disturbance
(Clark, 1990).
Ecological modeling needs human land use activities and how these changes influence spatial patterns
and movement of energy, species, and materials in urban environments. The historical trends in land use
and land cover provide not only an important perspective but a fundamental set of inputs for assessing
cumulative impacts at multiple temporal and spatial scales. However, as illustrated in Figure 4, land use
and land cover should be kept as separate categories. Models for integrated assessment, and integrated
regional models will certainly benefit from a richer set of temporal data resources for the landscape if
these data resources contain land cover structural and functional descriptions with accurate spatial
referencing (Pickett et al., 1994). The effects of land use practices and policies and their relationship to
vegetation can then be investigated with greater precision.
GIS provides the critical capacity for integrating historical documents with maps and remotely sensed
data to construct high quality regional environmental data repositories. The Baltimore-Washington
Regional Collaboratory (http://www.umbc.edu/bwrdc) represents an example of a regional data repository. The complex spatial nature of land cover and land use interactions requires GIS for managing these
datasets as inputs to comprehensive ecological assessments (Cowen et al., 1995; Stoms et al., 1992). The
specialization required to master this technology and to harness these information systems for ecological
assessments has, until recently, been a major obstacle for most multidisciplinary science teams. Spatial
statistics are increasingly being linked to remote sensing and GIS technology, enabling scientists to test
hypotheses and develop specialized models (Schlagel and Newton, 1996). With the advent of effective
modeling and visualization mechanisms to document, analyze, and present historical trends in land cover
and land use, a pronounced improvement in technical and interpretive capabilities exists for urban
ecosystem studies. Environmental modelers may wish to access land use and land cover data from a GIS
structure for model input or to calibrate their models (Oreskes et al., 1994; Schlagel and Newton, 1996;
Stoms et al., 1992). Modelers are clearly interested in integrating ecosystem components from GIS
databases to study and predict human influences on physical processes (Meyer, 1996; Bormann et al.,
1993; Grove, 1996). Ecological models use GIS object-oriented databases with relational database
management architectures to provide time sequential or time differential data analyses (Cowen et al.,
1995; Green and Cruise, 1995; Peuquet, 1994; Foresman et al., 1996). The greatest challenge facing the
modeling communities is integrating environmental, human, and physical models into a single set of
regional models (Blood, 1994; NSTC, 1995; Skole, 1994). Database managers, ecologists, and the
modeling community need to continue working together to creatively address issues of calibration,
Land use in the greater Baltimore-Chesapeake region
213
uncertainty and error propagation, simplification or aggregation, resolution, and scale. These are especially important for the development of regional models (Pacala, 1994).
Summary
The earth’s population has doubled in less than 50 years and within the past two decades the extent of
urbanization for the world’s major metropolitan areas has increased exponentially in both developed and
less-developed nations (Meyer, 1996). Urban land increased by 54 362 000 hectares in the United States
between 1960 and 1980 (Frey, 1984) and by 3 963 600 hectares in the Chesapeake watershed between
1980 and 1990 (NCRI, 1996). For the Chesapeake watershed, this decadal increase of approximately 40
to 60% in urban land use occupied nearly 10% of the watershed’s total acreage (NCRI, 1996; NRCS,
1996). By 1995, 21 world cities had populations of more than 6 million living in urbanized areas that
formerly supported agricultural or forest land cover and land use (World Almanac, 1996). The resulting
urbanization has drastically altered ecological patterns and processes. Using standard tools of GIS,
historical mapping, census data, and satellite imagery, studies on the east and west coasts have designed
procedures to spatially assess land cover and land use transitions and modifications (Kirtland et al., 1994;
Acevedo et al., 1996). Higher spectral and spatial resolution of historic land cover and land use databases
in combination with paleoecological core data may yield better analyses, but the analyses will depend on
the local resources and expertise available for specific geographic regions. Regardless, researchers
throughout the nation can benefit, at a minimum, from landscape level data by using an urban-to-rural
gradient approach to investigate urbanization impacts on ecological processes.
Acknowledgments
This research was supported in part by NASA Mission To Planet Earth Grants NAGW 5040 and NAGW
5070. We wish to thank Professor Grace Brush of Johns Hopkins University and Mike Ratcliffe of the
Bureau of the Census for sharing their research and providing review comments. We would also like to
thank Shawn Dalton for her review comments.
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