درخواست مجوز قابل معامله برای حفاظت از تنوع زیستی : اثرات عدم تجانس سود و زیان حفاظت وابسته به فضا بر تخصیص زیستگاه

This paper is concerned with the cost-effective allocation of habitat for species under spatio-temporally heterogeneous economic development. To address the dynamic dimension of the problem we consider tradable development rights as the instrument of choice. A particular challenge in applying tradable development rights is that the conservation benefit of an individual habitat patch depends on its spatial relationship with other habitat patches and thus is an emergent rather than a fixed property. We analyse with a conceptual model the spatial and temporal dynamics of habitats in a region under a tradable development rights market that takes spatial interaction of habitats explicitly into account. In our analysis two different outcomes may emerge depending on the levels of spatial interaction and cost heterogeneity: an “ordered” structure where habitat patches are clustered in space and are stable over time, and a “disordered” structure where habitat patches are scattered in space and subject to high turnover of destruction and recreation. A high level of spatial interaction or a low level of cost heterogeneity favours an ordered structure while a low level of spatial interaction or a high level of cost heterogeneity favours a disordered structure.

This paper is concerned with the problem that a conservation agency wishes to cost-effectively allocate a certain proportion of a region as conservation areas in a dynamic setting. With a dynamic setting we mean that economic development exists and land prices (representing opportunity costs of designating an area for conservation in terms of foregone economic development) change in a spatially heterogeneous manner. Cost-effectiveness is here understood as the achievement of an ecological target at least costs. At least in principle, the agency is able to select the cost-effective spatial allocation of conservation areas in a static setting (e.g. Ando et al., 1998 and Polasky et al., 2001). In a dynamic perspective, however, changing land prices may lead to a situation where the initially cost-effective selection is not cost-effective anymore. In order to re-establish a cost-effective allocation, the agency would be confronted with the problem of designating new areas for conservational purposes and allowing economic development in former conservation areas. Such a bureaucratic approach requires a high level of information about cost changes on the side of the agency and is also very sensitive to political lobbying activities regarding the questions which areas shall be released for economic development and which areas shall be designated for conservation. An alternative to this bureaucratic approach to addressing changing land prices are tradable development rights. Based on the concept of tradable permits, such a system would allow economic development of a formerly conservation area if a permit is submitted to the conservation agency which certifies that an area with previously no conservation value has been transformed back into a conservation area of ecological value equal to the area to be destroyed. There is no requirement that developers establish new habitats themselves, but the permit can be bought from other landowners. This allows a market for tradable development rights to emerge.

We modelled a market for development rights in a landscape where land patches can either be used as habitat or for economic purposes. Land owners trade rights to destroy habitat and use it for economic development. The costs (in terms of foregone economic development) of using a patch as habitat differ among patches and vary over time. Space plays an important role in that the ecological value of a habitat patch depends on its location; in particular, to what extent other habitat patches exist in its vicinity. Based on ecological theory (e.g., Hanski, 1999, Vos et al., 2001 and Ovaskainen and Hanski, 2003), we assumed that the ecological value of a habitat patch increases when more habitat patches are found in its neighbourhood. A similar assumption has been made by Parkhurst et al. (2002) who designed a payment scheme for conservation measures which contains a bonus payment for habitat adjacency. In our model, this spatial interaction leads to self-organised dynamics of habitat creation and destruction in the considered landscape. Being interested in the stationary behaviour of the model, we found two possible phases the dynamics can be in: an ordered or a disordered phase. In the ordered phase the patches containing habitat are clustered in space, while in the disordered phase they are scattered. The ordered phase is obtained if the variation in the costs lies below a critical value that is determined by the spatial interaction between the ecological values of the habitats. If the value of a habitat patch very strongly depends on the presence of other habitat patches in its neighbourhood, the ordered phase is maintained even at high cost variation. If the variation in the costs exceeds the critical value, the system switches into a disordered phase. In a way, the dynamics can be seen as a struggle between two forces: the interaction between the ecological values of the habitat patches is the ordering force that leads to a clustering of habitat patches; the random variation in the costs tends to tear habitat clusters apart and lead into disorder. The outcome of the dynamics is determined by the prevailing force.