Grantee Research Project Results
Final Report: Economics of Conserving Ecosystem Integrity with Residential Development around Vernal Pools
EPA Grant Number: R829384Title: Economics of Conserving Ecosystem Integrity with Residential Development around Vernal Pools
Investigators: Swallow, Stephen K. , Paton, Peter
Institution: University of Rhode Island
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2005 (Extended to August 31, 2006)
Project Amount: $200,017
RFA: Decision-Making and Valuation for Environmental Policy (2001) RFA Text | Recipients Lists
Research Category: Environmental Justice
Objective:
The purpose of this research is to develop a framework for identifying and understanding the economic and ecological factors that influence society’s ability to maintain well-functioning ecosystems in the face of sprawl or urban development. Particular emphasis is given to modeling the effects of residential development on amphibian metapopulations dependent upon vernal pools and upland habitats connecting these pools. Objectives of the research include: (1) assessing the baseline value of foregone opportunities for development and amphibian metapopulations that can be anticipated after rural residential development expands under current regulations; (2) evaluating the economic and ecological factors affecting the cost of maintaining metapopulations for an assemblage of amphibians, as represented by vernal pool ecosystems in southern New England; and (3) examining the economic and ecological implications of alternative regulatory or development incentive mechanisms that influence the probability of land development within or around vernal pool based ecosystems.
Summary/Accomplishments (Outputs/Outcomes):
The research has produced results in three major areas. First, a conceptual model has been developed to incorporate long-term persistence of amphibians using seasonal wetlands in a landscape undergoing residential development. Second, a simulation application has been developed, drawing from literature on amphibian ecology and on economic data pertaining to southwestern Rhode Island. Third, a simulation has been completed to evaluate the implications for wetland regulatory policy, particularly at the state or local level; these policies might improve the ability of the landscape to sustain amphibian populations while allowing residential development to proceed in balance with land conservation.
The ecological modeling is based on the theory of metapopulations, which are populations of a species that exist in separate subpopulations in each patch of suitable habitat; these subpopulations interact to establish and sustain the overall population. Amphibians are often modeled as metapopulations because the subpopulation breeding in a particular pond (especially seasonal ponds) are viewed as unable to survive in the long term because each pond (a habitat patch) may undergo conditions in some years that cause its subpopulation of amphibians to die off. That habitat patch may then be recolonized by individuals dispersing from other habitat patches. In this manner, a collection of ponds (habitat patches) across the landscape maintains the full population of the species.
Review of the theoretical biology literature identified two related constructs, developed by Illka Hanski and Otso Ovaskainen, for assessing long-term persistence of metapopulations based on spatially realistic landscape data. The metapopulation persistence capacity, similar to a single-population carrying capacity, measures a landscape’s ability to support viable metapopulations over the long term. The metapopulation size measures the average occupancy of habitat patches, reflecting the rarity or commonness of the target species throughout the landscape. Both constructs take into account the quantity and quality of habitat available, the spatial configuration of the habitat patch network, and species-specific dispersal parameters. The choice between metapopulation persistence capacity or metapopulation size in the constraint depends on the question being asked; metapopulation persistence capacity is more appropriate for examining rare and endangered species in a highly fragmented landscape, whereas metapopulation size is more appropriate for assessing the long-term persistence of a common species throughout the landscape. The conceptual model allows for both types of analyses. We expanded the metapopulation persistence capacity and metapopulation size constructs to incorporate the effects of residential development on habitat patches and the barriers to dispersal between patches; we then used the revised measures as constraints within the conceptual model.
Review of the economics literature identified a combination of Von Thunen (location-oriented) and Ricardian (quality-oriented) land rents as the appropriate measure for residential development benefits. Development is assumed to have irreversible effects on the landscape. Conceptually, the model shows the opportunity costs associated with foregone development benefits that result from achieving long-term metapopulation persistence. Mathematically, the model maximizes the benefits from various developed land uses, subject to an ecological constraint that maintains the landscape’s metapopulation persistence capacity (or metapopulation size) above the safe minimum standard deemed appropriate by a community (such as articulated through a town planning board or conservation commission). Analyses show that the opportunity costs associated with foregone development increase non-linearly with increasing probability of persistence (or increasing average occupancy). That is, the costs of achieving the safe minimum standard increase at an increasing rate.
The conceptual model was applied to a 10,000-acre landscape containing 123 vernal pools within the Wood–Pawcatuck watershed in western Rhode Island. A ponds-as-patches approach was used to define the landscape structure. Vernal pool (seasonal wetland) and other landscape data including patch size and distance between patches, obtained from the Rhode Island Geographic Information System (RIGIS), were used to generate the landscape matrix used in calculating the metapopulation persistence capacity and metapopulation size. Species-specific parameters for wood frogs (Rana sylvatica) were extrapolated from existing amphibian literature. An ordinary least squares (OLS) regression was performed on the tax assessor data, generating estimates of the per-acre land values. A MATLAB program was developed to perform numerical optimizations based on the conceptual model described above. A series of optimizations varying the metapopulation size over its entire range produced a baseline cost function that represents the “optimal” solution. This is shown in Figure 1 as the line. The curve represents the tradeoff between the economic benefits of residential development and the ecological benefits of land preservation.
A number of policy scenarios (Table 1) were simulated and compared to the optimal solution. One obvious result is that it is possible to achieve a relatively high metapopulation size for a relatively minimal cost. This is due to the initial elimination of small isolated patches and large “empty” spaces between patches. A second key result is that current policies which only protect the wetland or a small buffer around the wetland, result in long-term metapopulation extinction (they fall to the far left off the graph in Figure 1). Alternative policies that protect larger buffers or some of the intervening landscape matrix perform better, but still don’t achieve the optimal solution. Market-based policy alternatives such as impact fees or transferable development rights may be required.
Table 1. Descriptions of Policy Alternatives
Policy Alternative |
Description1 |
Current 1 (C1) |
Current wetland policy that protects the area of the pool only |
Current 2 (C2) |
Same as C1 except developed parcels are two acres |
Envelope (E) |
Protect vernal pool plus 100-foot buffer (envelope) |
Guidelines (G) |
Protect vernal pool plus 100-foot buffer plus 75% of critical habitat;2 recommended vernal pool guidelines3 |
New Policy 1 (P1) |
Protect vernal pool plus 100-foot buffer plus 50% of critical habitat |
New Policy 2 (P2) |
Protect vernal pool plus 100-foot buffer plus 25% of critical habitat |
New Policy 3 (P3) |
Protect vernal pool plus 100-foot buffer plus 25% of critical habitat plus 25% of intervening landscape matrix |
No Development (0) |
Protect all vernal pools plus 100-foot buffer plus 100% critical habitat plus 100% of intervening landscape |
1Unless otherwise noted, all policies assumed all developed parcels were one acre. |
2Critical habitat is defined as an outer buffer 100-750 feet from pool edge. |
3Vernal pool guidelines (described in Calhoun and Klemens, 2002). |
Figure 1. Comparison of the Opportunity Costs Associated With Foregone Development Corresponding to Various Conservation–Oriented Policy Alternatives (Table 1)
The land allocation framework presented above is simplistic in terms of homogeneity of land values and habitat quality. To provide for a more robust analysis, additional GIS data were generated that included a variety of parcel-level characteristics (e.g., slope, soils, elevation, distance to town center, distance to highway, quantity of neighborhood open space, distance to major employment centers, etc.). These data have been combined with tax assessor data to estimate heterogeneous land values and allow the land value to respond to these GIS-based characteristics. Through a simulation analysis, these economic data were combined with data on the breeding activity of amphibians in particular ponds. Amphibian data rely on counts of egg-masses and this database was used to identify heterogeneity of habitat quality.
The primary model divided the landscape into habitat patches centered around ponds with either a 165-m or a 229-m buffer zone. Land existing outside of these patches was allocated to the category of “landscape matrix.” These designations of land capture the gross ecological role that land elements play in the metapopulation modeling: habitat patches versus matrix lands which individuals of a species cross as they disperse between patches. Based on review of the amphibian literature and discussions with amphibian ecologists, it was decided to treat pond clusters (i.e., ponds within 100 m of each other) as a single habitat patch.
To accommodate different land uses in a more robust model, the landscape has also been divided into “neighborhoods” (or management units) based on current zoning districts for the application area in southwestern Rhode Island. These neighborhoods generally contained one or more habitat patches and some portion of landscape matrix.
The neighborhoods allowed for assessment of a wider range of policy alternatives. In addition, the 10,000-acre parcel landscape matrix was expanded to encompass an entire town within the Wood–Pawcatuck watershed of southwestern Rhode Island. This new landscape matrix uses patch areas, the two different buffer sizes (mentioned above), distances between patches, percentage of distances in each of 16 neighborhoods, existing development densities in each patch and each neighborhood, and patch qualities for 214 vernal pools distributed across 25,000 acres.
Theoretical Results
The economic model was defined as a Ricardian land rent model, taking the analytical construct of a social planner (such as a town planner) who establishes policies in order to maximize the value of land remaining available for development while sustaining a particular metapopulation size of amphibians. The policy variables define the proportion of each habitat patch and the proportion of matrix land within each “neighborhood” management unit to protect from development. The model includes consideration of the ecological quality of habitat patches, as represented by egg-mass counts estimated for each patch, and the distances the target species of amphibians would have to cross between habitat patches. Development is modeled to decrease the permeability of matrix land to amphibians dispersing between ponds, and development reduces the effective area (and therefore the ecological quality) of a habitat patch that undergoes partial development.
Analytical analysis showed the following items to be balanced by a cost-effective policy to achieve the target metapopulation size. First, the marginal value of one unit of developable land, whether in patch or matrix, must balance the opportunity cost of using that unit of land in support of land conservation (i.e., in support of the metapopulation size). This basic result implies that cost-effective policy will balance the ratio of (i) the impact of a unit (acre) of land placed in conservation on improving the metapopulation capacity of the landscape to (ii) the monetary value of that unit of land if it remained available for development. This ratio needs to be balanced across all land types (i.e., across habitat-patch and matrix acres with different attributes in the GIS data, such as slope, land-cover type, elevation, access to highways and village centers, and others). This result implies that land with higher development value will be more often allocated toward development, but cost-effective policy will encourage that allocation in relation to the role of land in the ecological quality represented by metapopulation capacity. The result also implies a departure from common policy toward wetlands, in that cost-effective policy recognizes that some conservation of matrix lands is appropriate while common policies tend to focus heavily or exclusively on the wetland patch alone.
Analytical results also indicate that pre-existing development may, in some patches or matrix neighborhoods, have gone beyond the level that cost-effective policy would have recommended if a policy assessment had been conducted earlier. Given current conditions of development and conservation value of land, some patches may be allowed to experience some additional development, other patches would be protected from any further development; similarly, some matrix neighborhoods could be protected from further development while others would be left for some degree of additional development. The cost-effective model encourages a careful balancing across all patches and matrix lands within management “neighborhoods” associated with zoning areas, rather than encouraging an exclusive focus of policy to protect wetlands and a pre-defined buffer zone from any development at all.
These results also indicate that an empirically-based model is needed to carefully distinguish the appropriate distribution of land that a cost-effective policy should encourage within a patch or a matrix. Ecological parameters may imply that preservation should actually focus on the matrix land outside of wetland habitat patches due to the ability of the species to disperse between patches and the role of patch-acres in sustaining the metapopulation. In other portions of the landscape, this cost-effective policy might encourage protection of a higher proportion of land associated with habitat patches rather than with matrix. In short, factors affecting the ecology of species and factors affecting the preferences of humans for land lead to policy recommendations that may vary across a landscape. The policy advice may be incorporated within a zoning-type framework in order to tailor policy to the ecological and economic factors that determine alternatives that maintain ecological criteria while allowing for the maximum value of land available for development.
Landscapes with a greater distance between patches, or applications involving species with a lower dispersal ability, will require a higher proportion of preservation generally (although not necessarily in every zone or neighborhood) in order to sustain an environmental goal indicated by a metapopulation size of the target species. Heterogeneity of the land, for both ecological conservation or development uses, implies that the proportion of land preserved in habitat patches may or may not exceed the proportion of land preserved in matrix “neighborhoods” outside of habitat patches. By allowing for flexibility in the proportion of land preserved from development across patches and matrix lands, it is possible to sustain a particular metapopulation capacity at a substantially lower loss of development value than is likely with common policies that focus exclusively on preservation of habitat patches.
Issues Identified for Future Research. This study was based, primarily, on an analysis of species persistence and development value that would occur once a community has grown to its maximum capacity for residential development, sometimes called “full build out.” This approach sets aside additional issues that could be evaluated in a future, dynamic model. First, the development process itself may adversely affect ecosystem functions and the target or indicator species on which policy is based. Temporary barriers to dispersal, such as through large-scale development of multiple homes and corresponding roads, could produce sufficient ecological impacts to cause substantial loss or even extinction of the species in all or part of a planners’ jurisdiction prior to full build out. Second, the choice of policy instruments (purchase of development rights, incentive policies, or zoning and regulatory restrictions) could influence the time-path of land conservation while development proceeds. This process could alter the absolute or relative opportunity costs (i.e., development values) of land in different patches or matrix neighborhoods over time. A dynamic analysis may be needed to understand the impacts of these policy choices on cost-effective planning. Third, the dynamic modeling approach may be essential to a region with significant exploitation of renewable resources, such as a region under timber management. The research conducted here could provide useful background for such a model. Fourth, while the model developed here allowed some consideration of the role of land restoration in a comprehensive policy, restoration of road corridors or building sites in a dynamic analysis may imply additional policy concerns that have not been fully addressed at this time.
Stylized Application to Town of Richmond, Rhode Island
Drawing on the literature of amphibian ecology, the study obtained a collection of representative parameters for dispersal, effectiveness of patch-area for supporting amphibians, parameters related to the likelihood that the subpopulation in a habitat patch dies out (local extinction threshold), and parameters related to the impact of zoning rules for residential density (e.g., acres required per home) on the effective area remaining for amphibians in habitat patches or matrix neighborhoods. These parameters are reported in Bauer (2005, p. 86) and are indicative of likely conditions for Richmond, Rhode Island and wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum). However, not all parameters were obtained through original sources related to Richmond, so the application must be viewed as a stylized application that indicates a range of possible results. Nonetheless, the economic parameters, particular land values, and the landscape attributes, such as the location of habitat patches and zoning-area boundaries, were taken from Richmond. The town of Richmond includes nearly 25,000 acres in 16 management units defined by a combination of zoning boundaries and major roads, and 214 habitat patches.
Simulation results show that uniform policies applied to all patch or matrix lands may achieve a particular value of metapopulation size (average proportion of patches occupied by the target species in a year) at substantially higher cost than would be incurred through a flexible policy to achieve the same metapopulation size cost-effectively. Here, cost is measured as the value of land held for conservation rather than placed into development, and this measure is derived from the estimated value of unimproved, vacant land in Richmond. For example, a policy to preserve 100% of remaining undeveloped land in habitat patches that include a 165-m buffer, and 25% land in matrix neighborhoods would cost approximately $230 million.
Yet the same metapopulation size (90% of ponds occupied by spotted salamanders) could be achieved by the most flexible, cost-effective policy for under $15 million. However, this flexible policy implies a different proportion of conservation for each of 214 habitat patches and each of their associated matrix neighborhoods. A compromise that might reduce the administrative burden of such a detailed, flexible policy would be to aggregate Richmond’s land area into five distinct sections and to apply a uniform policy for conservation of patch and matrix lands within each section, but not necessarily preserving the same proportion of patch or matrix lands within each section. This compromise policy could achieve the same metapopulation size for under about $35 million in foregone development value, representing a savings of nearly 85% relative to applying the uniform policy across all patches and matrix lands.
The research reported in Bauer (2005) and manuscripts under review for refereed publication provides details on how these cost estimates may be sensitive to assumptions of alternative ecological and landscape parameters. However, results consistently showed that a substantial savings (generally well in excess of 50%) in the value of land allocated to conservation rather than development could be achieved through evaluation using the economic–ecological framework developed in this research. Alternatively, the model could be applied to identify a higher level of metapopulation size that could be obtained for a cost that a community is willing to incur in terms of foregone development.
In general, simulations showed that landscapes with larger habitat patches and a higher density of patches resulted in higher levels of metapopulation persistence. But even the high density of patches in the study area did not preclude the need to protect some portion of the matrix of land outside of habitat patches. Policies that treat habitat patches independently, allowing for some patches to be largely developed and others to be largely or entirely preserved while also assuring a balance of preservation of matrix lands, typically imposed the lowest cost in terms of foregone development value while achieving a chosen metapopulation goal.
Challenges Facing Applications. A significant challenge facing applications of the economic–ecological model developed here is the judgment that currently must occur in defining patch sizes, matrix lands, and management units for zoning purposes. Additional ecological research could establish methods that allow biological conditions to define patch sizes, for example, so that a patch size may not be defined by a researcher’s choice of the buffer zone around seasonal ponds. Interdisciplinary research, which integrates economics and ecology, may prove critical to improving upon the research completed here. This may include research to improve numerical optimization methods and to establish and enrich a broad array of data available for integration in a geographic information system. However, given the potential savings in the cost that communities might face to achieve a desirable ecological standard, there is room to justify funding such research.
Addendum
A comprehensive reporting of the technical details is elaborated in the Ph.D. Dissertation by Dana Marie Bauer (2005; “Cost-Effective Land Development with a Spatially Realistic Ecosystem Constraint.” University of Rhode Island, 234pp.). This dissertation is available through the UMI Dissertation Services of Ann Arbor, Michigan, as well as through the University of Rhode Island.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 26 publications | 11 publications in selected types | All 7 journal articles |
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Type | Citation | ||
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Bauer DM, Paton PWC, Swallow SK. Are wetland regulations cost effective for species protection? A case study of amphibian metapopulations. Ecological Applications 2010;20(3):798-815. |
R829384 (Final) |
Exit |
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Egan RS, Paton PWC. Within-pond parameters affecting oviposition by wood frogs and spotted salamanders. Wetlands 2004;24(1):1-13. |
R829384 (2002) R829384 (2003) R829384 (2004) R829384 (Final) |
Exit Exit |
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Montieth KE, Paton PWC. Emigration behavior of spotted salamanders on golf courses in Southern Rhode Island. Journal of Herpetology 2006;40(2):195-205. |
R829384 (2004) R829384 (Final) |
Exit Exit |
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Paton PWC, Egan RS, Osenkowski JE, Raithel CJ, Brooks RT. Rana sylvatica (wood frog) breeding behavior during drought. Herpetological Review 2003;34(3):236-237. |
R829384 (2003) R829384 (2004) R829384 (Final) |
not available |
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Paton PWC. A review of vertebrate community composition in seasonal forest pools of the northeastern United States. Wetlands Ecology and Management 2005;13(3):235-246. |
R829384 (2004) R829384 (Final) |
Exit Exit |
Supplemental Keywords:
RFA, Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, Economics, decision-making, Ecology and Ecosystems, Economics & Decision Making, Social Science, ecological exposure, ecosystem integrity, vernal pool ecosystems, decision making, wetland regulation, cost-effective ecosystem protection, environmental values, environmental policy, residential development, ecosystem integrity and residential development, vernal pools, community-based, conservation biology, public policy, cost-effective ecosysem protection, conserving ecosystem integrityProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.