28.5 Spatial Models of Human Impacts on Ecosystems
towns may be retarded, resulting in increased in
situ rural densities, and rural to rural migration and
urban to rural migration expands. These processes
extend the agricultural frontier and raise rural population densities.
In industrialized countries, extensive primary activities, such as agriculture, are generally associated with low population densities. Although immigration to cities has slowed, urban populations
continue to increase and suburbanization is occurring rapidly, resulting in conversion of agricultural
land. There is also a pattern of land conversion to
residential uses for retirement and second homes
characterized by areas with desirable environmental conditions such as forests and water bodies. An
increase in recreational facilities, road and public
utility infrastructure, and service activities augment
the residential land-use pattern, and forest and land
cover fragmentation and altered edge features often ensue with implications for ecosystem functions
and processes, including wildlife habitats, biodiversity conservation, albedo, and carbon cycling.
28.5 Spatial Models of Human
Impacts on Ecosystems
Many ecologists as well as social scientists recognize that prediction is limited by uncertainties about
the nature of social and ecological systems. Increasing numbers argue that there is a need to move
beyond the search for regularity and predictability
as a basis for explanation. They recognize that these
systems and the processes that determine society-environment interaction often include nonlinear relationships, and that there are temporal, spatial, and scalar characteristics of the interactions
that defy determinism, or even determinism modified by stochastic processes. Also, critical variables, such as time, scale, and power, and the influences of values, beliefs, preferences and mores
are too often omitted from the analysis.
These criticisms are significant, but they should
not be used to dismiss the utility of data-based models. They do, however, demonstrate that models
should not be used for policy making without explicit attention to the assumptions and caveats of
the model builders and to the insights of indigenous knowledge systems (Warren, 1991; Seeland,
1997). This calls for a more robust approach, which
can include both quantitative and qualitative information from a variety of sources. Such approaches
would value not only data-based models, but also
modeling strategies such as decision-making models and role-playing simulations.
423
28.5.1 Land-use Models
A variety of models have been developed to model
land-use changes. The majority assumes that market forces dominate determination of the optimum
utility of land and the location of economic activity. Industrial location theory assesses the relative
importance of economic factors of land labor and
capital and external and internal economies of the
firm. Other models that generalize from the level
of the firm to that of land-use patterns and argue
that a bid rent process induces patterns of land use
include von Thunen's model of agricultural land
use and the urban land-use models associated with
central place theory. Such models are illustrated in
Haggett (1983) and in Stutz and de Souza (1998).
These models are predicated on the concept that
land uses such as agriculture, industry, and commerce have specific requirements that make some
locations more desirable than others. These include
towns as markets for agricultural products, city centers as foci for commerce, and, for industry, places
with available land and access to transport infrastructure. These desirable locations may be identical for different activities, in which case they will
bid against each other. The outcome will reflect the
will and ability of each potential land use to outbid others.
Although economic processes dominate these
models, there is recognition that political, cultural,
and historical factors may alter the outcome (Harvey, 1973; Massey, 1984). Furthermore, there exists an inertia of the created environment that constrains replacement of one land use with another
that achieves optimum spatial economic utility.
Such inertia may result from the existence of buildings that represent a significant investment, regulations reflecting historical or cultural considerations, and externalities such as the presence of toxic
wastes.
28.5.2 Demographic Projections
Population dynamics reflect the relationship between births and deaths and the redistribution of
population through migration. For any particular
region the growth or decline of population can be
calculated as
population growth
= (births - deaths) + (immigrants - emigrants)
Historical assessments of this relation have resulted
in the categorical demographic transition model
(Figure 28.1), which in its original formulation
identified four stages that reflect changes in the bal-
towns may be retarded, resulting in increased in
situ rural densities, and rural to rural migration and
urban to rural migration expands. These processes
extend the agricultural frontier and raise rural population densities.
In industrialized countries, extensive primary activities, such as agriculture, are generally associated with low population densities. Although immigration to cities has slowed, urban populations
continue to increase and suburbanization is occurring rapidly, resulting in conversion of agricultural
land. There is also a pattern of land conversion to
residential uses for retirement and second homes
characterized by areas with desirable environmental conditions such as forests and water bodies. An
increase in recreational facilities, road and public
utility infrastructure, and service activities augment
the residential land-use pattern, and forest and land
cover fragmentation and altered edge features often ensue with implications for ecosystem functions
and processes, including wildlife habitats, biodiversity conservation, albedo, and carbon cycling.
28.5 Spatial Models of Human
Impacts on Ecosystems
Many ecologists as well as social scientists recognize that prediction is limited by uncertainties about
the nature of social and ecological systems. Increasing numbers argue that there is a need to move
beyond the search for regularity and predictability
as a basis for explanation. They recognize that these
systems and the processes that determine society-environment interaction often include nonlinear relationships, and that there are temporal, spatial, and scalar characteristics of the interactions
that defy determinism, or even determinism modified by stochastic processes. Also, critical variables, such as time, scale, and power, and the influences of values, beliefs, preferences and mores
are too often omitted from the analysis.
These criticisms are significant, but they should
not be used to dismiss the utility of data-based models. They do, however, demonstrate that models
should not be used for policy making without explicit attention to the assumptions and caveats of
the model builders and to the insights of indigenous knowledge systems (Warren, 1991; Seeland,
1997). This calls for a more robust approach, which
can include both quantitative and qualitative information from a variety of sources. Such approaches
would value not only data-based models, but also
modeling strategies such as decision-making models and role-playing simulations.
423
28.5.1 Land-use Models
A variety of models have been developed to model
land-use changes. The majority assumes that market forces dominate determination of the optimum
utility of land and the location of economic activity. Industrial location theory assesses the relative
importance of economic factors of land labor and
capital and external and internal economies of the
firm. Other models that generalize from the level
of the firm to that of land-use patterns and argue
that a bid rent process induces patterns of land use
include von Thunen's model of agricultural land
use and the urban land-use models associated with
central place theory. Such models are illustrated in
Haggett (1983) and in Stutz and de Souza (1998).
These models are predicated on the concept that
land uses such as agriculture, industry, and commerce have specific requirements that make some
locations more desirable than others. These include
towns as markets for agricultural products, city centers as foci for commerce, and, for industry, places
with available land and access to transport infrastructure. These desirable locations may be identical for different activities, in which case they will
bid against each other. The outcome will reflect the
will and ability of each potential land use to outbid others.
Although economic processes dominate these
models, there is recognition that political, cultural,
and historical factors may alter the outcome (Harvey, 1973; Massey, 1984). Furthermore, there exists an inertia of the created environment that constrains replacement of one land use with another
that achieves optimum spatial economic utility.
Such inertia may result from the existence of buildings that represent a significant investment, regulations reflecting historical or cultural considerations, and externalities such as the presence of toxic
wastes.
28.5.2 Demographic Projections
Population dynamics reflect the relationship between births and deaths and the redistribution of
population through migration. For any particular
region the growth or decline of population can be
calculated as
population growth
= (births - deaths) + (immigrants - emigrants)
Historical assessments of this relation have resulted
in the categorical demographic transition model
(Figure 28.1), which in its original formulation
identified four stages that reflect changes in the bal-