412
Characterizing the Human Imprint on Landscapes for Ecological Assessment
spatial units (e.g., watersheds) by making assumptions or adding information about the spatial distributions of a quantity (e.g., population density)
within a set of enumeration units (e.g., counties or
tracts). This process, called areal interpolation, can
be carried out using techniques outlined by Tobler
(1979), Flowerdew and Green (1989), Langford et
ai. (1991), Martin and Bracken (1991), and Goodchild et ai. (1993). A common assumption for many
of these methods is that the value of the variable
(say, population density) is constant throughout
each unit (Langford et aI., 1991). Tobler's (1979)
method relaxes this assumption by assuming
smooth variation of a population density surface.
The method of Goodchild et al. (1993) relaxes this
assumption by employing control units that are
more likely to satisfy the homogeneity assumption.
None of these methods is without error, and it is
important to acquire data measured directly for geographic areas of interest in an assessment (e.g.,
watersheds) if at all possible.
27.3.2 Ownership Boundaries
The goals and rules of land management vary depending on who owns the land. Land might be held
in private hands (e.g., corporate or personal) or by
public agencies (e.g., federal, state, or local). Each
class of owner has a different set of constraints on
use and management defined by the economy, law,
culture, tax systems, and regulations.
The system of publicly held lands in the United
States is a legacy of initial settlement policy, various preservation-oriented initiatives, and tax delinquencies that caused private land to revert back to
public ownership. Governmental agencies that own
lands can provide information about the locations
and management of these lands. This information
is often not up to date or in a form readily accessible for analysis, but data quality is improving. The
U.S. Geological Survey maintains boundary files
for land owned by a number of federal, state,
county, and local agencies, stored as DLGs (Table
27.4). These files, however, are rarely complete or
recent. To address the needs by the Gap Analysis
Program (GAP) for information on the locations of
public lands, as well as attribute information on the
level of management for wildlife and habitat
preservation, McGhie et al. (1996) compiled the
managed areas database (MAD) at a scale of
1 : 2,000,000, for the conterminous United States.
The database includes attributes on area name, designation, protection status, level of management,
and data source. A variety of sources was used for
this database, most of which ultimately came from
the U.S. Geological Survey and the Bureau of Land
Management.
Private lands are much more difficult to characterize, because many more different individuals and
entities manage them and because they change
hands more frequently than public lands. In some
areas of the United States, plat map books are produced on a regular basis, which show the boundaries of ownership parcels and list the names of
owners (Rockford Map Publishers, 1998). One
trend that should improve the availability of information about private lands in the United States is
the increasing tendency for county and local tax offices to maintain digital versions of their maps of
parcels. The need for this information for ecological assessment is such that there should be no need
to invade the privacy of individuals. A useful attribute of private land ownership is simply whether
the owner is a corporation or an individual. Other
important attributes include the size of parcels and
diversity of owners in a given area, which can affect the land use-cover and the ability to manage
or intervene in a ecosystem's function.
Many rural areas in the United States are experiencing declines in ownership parcel sizes on private lands that have a variety of implications. In a
recent study of parcel sizes in rural areas of the
forested upper Midwest, initially reported by
Brown and Vasievich (1996), average parcel sizes
were shown to have declined an estimated 1.2% per
year between 1960 and 1990. Higher rates of decline were observed in the 1970s, when rural population growth rates were highest. Trends such as
these have implications for how land is or can be
used, the spatial patterning of land use and land
cover, and appropriate landscape management approaches.
27.3.3 Land Use
Land use is the intangible relative of land cover and
refers to the way in which the land is managed for
human goals. The management of land is a very
important, but difficult, factor to characterize. The
way the land is managed will have indirect, and
sometimes direct, effects on what cover results and
on the aspects of this cover (e.g., intensity) that affect ecosystem function. At the same time, land use
is reflective of the socioeconomic forces driving
landscape changes. Changes in demographic, economic, political, and institutional characteristics often lead to changes in land use (e.g., Vesterby and
Heimlich, 1991). Land management practices are
included as a factor (P) in the universal soil loss
equation (USLE) for characterizing average annual
Characterizing the Human Imprint on Landscapes for Ecological Assessment
spatial units (e.g., watersheds) by making assumptions or adding information about the spatial distributions of a quantity (e.g., population density)
within a set of enumeration units (e.g., counties or
tracts). This process, called areal interpolation, can
be carried out using techniques outlined by Tobler
(1979), Flowerdew and Green (1989), Langford et
ai. (1991), Martin and Bracken (1991), and Goodchild et ai. (1993). A common assumption for many
of these methods is that the value of the variable
(say, population density) is constant throughout
each unit (Langford et aI., 1991). Tobler's (1979)
method relaxes this assumption by assuming
smooth variation of a population density surface.
The method of Goodchild et al. (1993) relaxes this
assumption by employing control units that are
more likely to satisfy the homogeneity assumption.
None of these methods is without error, and it is
important to acquire data measured directly for geographic areas of interest in an assessment (e.g.,
watersheds) if at all possible.
27.3.2 Ownership Boundaries
The goals and rules of land management vary depending on who owns the land. Land might be held
in private hands (e.g., corporate or personal) or by
public agencies (e.g., federal, state, or local). Each
class of owner has a different set of constraints on
use and management defined by the economy, law,
culture, tax systems, and regulations.
The system of publicly held lands in the United
States is a legacy of initial settlement policy, various preservation-oriented initiatives, and tax delinquencies that caused private land to revert back to
public ownership. Governmental agencies that own
lands can provide information about the locations
and management of these lands. This information
is often not up to date or in a form readily accessible for analysis, but data quality is improving. The
U.S. Geological Survey maintains boundary files
for land owned by a number of federal, state,
county, and local agencies, stored as DLGs (Table
27.4). These files, however, are rarely complete or
recent. To address the needs by the Gap Analysis
Program (GAP) for information on the locations of
public lands, as well as attribute information on the
level of management for wildlife and habitat
preservation, McGhie et al. (1996) compiled the
managed areas database (MAD) at a scale of
1 : 2,000,000, for the conterminous United States.
The database includes attributes on area name, designation, protection status, level of management,
and data source. A variety of sources was used for
this database, most of which ultimately came from
the U.S. Geological Survey and the Bureau of Land
Management.
Private lands are much more difficult to characterize, because many more different individuals and
entities manage them and because they change
hands more frequently than public lands. In some
areas of the United States, plat map books are produced on a regular basis, which show the boundaries of ownership parcels and list the names of
owners (Rockford Map Publishers, 1998). One
trend that should improve the availability of information about private lands in the United States is
the increasing tendency for county and local tax offices to maintain digital versions of their maps of
parcels. The need for this information for ecological assessment is such that there should be no need
to invade the privacy of individuals. A useful attribute of private land ownership is simply whether
the owner is a corporation or an individual. Other
important attributes include the size of parcels and
diversity of owners in a given area, which can affect the land use-cover and the ability to manage
or intervene in a ecosystem's function.
Many rural areas in the United States are experiencing declines in ownership parcel sizes on private lands that have a variety of implications. In a
recent study of parcel sizes in rural areas of the
forested upper Midwest, initially reported by
Brown and Vasievich (1996), average parcel sizes
were shown to have declined an estimated 1.2% per
year between 1960 and 1990. Higher rates of decline were observed in the 1970s, when rural population growth rates were highest. Trends such as
these have implications for how land is or can be
used, the spatial patterning of land use and land
cover, and appropriate landscape management approaches.
27.3.3 Land Use
Land use is the intangible relative of land cover and
refers to the way in which the land is managed for
human goals. The management of land is a very
important, but difficult, factor to characterize. The
way the land is managed will have indirect, and
sometimes direct, effects on what cover results and
on the aspects of this cover (e.g., intensity) that affect ecosystem function. At the same time, land use
is reflective of the socioeconomic forces driving
landscape changes. Changes in demographic, economic, political, and institutional characteristics often lead to changes in land use (e.g., Vesterby and
Heimlich, 1991). Land management practices are
included as a factor (P) in the universal soil loss
equation (USLE) for characterizing average annual