Land-use change due to human population and economic growth has been one of the major drivers of environmental change over the last 100 years. As a result native habitats have been reduced and fragmented, causing a loss of biodiversity and ecosystem services. Evaluating how alternative policies can affect the trajectory of land-use change in the conterminous U.S.A., and estimating the resulting changes in terrestrial carbon storage and habitat of native vertebrates, will provide information useful for decision-makers.
Our approach started with econometric models based on observed landowner behavior that predict likely land-use changes as a function of current land-use conditions, public policy and market opportunities. Land market dynamics were incorporated into the modeling approach to reflect supply and demand of land in various uses, thereby capturing land-market feedback effects that have been largely ignored to date in the conservation literature. Projected land-use changes on private lands in broad categories from 2002-2052 were then translated into changes in fine-scale habitat types that are biologically relevant to vertebrates. We compared alternative policy scenarios (forest conservation, forest/grassland/shrubland conservation, urban growth constraints, and increasing crop prices) to a baseline or "business-as-usual" scenario. We modeled the responses of 230 vertebrate species based on changes in the amount of both marginal and prime habitat within their species ranges. In addition, a continental-level carbon storage model was used to estimate changes in land-use specific carbon storage (both soil and aboveground).
Results/Conclusions
The dominant land-use change in all scenarios was increases in urban lands (up by 90%), followed by increases in forest lands (up by 6%) at the expense of other land uses. The forest conservation scenario showed the greatest potential for higher amounts of carbon storage (relative to the baseline). In all scenarios the amount of habitat for vertebrates on our list decreased on average compared to current levels, though there was a wide range of responses across different species. Relative to the baseline scenario, the forest/grassland/shrubland conservation scenario showed the greatest potential for preserving more habitat for a variety of vertebrate species, though not by large amounts (e.g., a median 3% more prime habitat compared to baseline). Although incentives similar to those we modeled in our policy scenarios may be an important part of providing habitat in the future on privately-held lands, in the face of continued population growth and demand for urban lands, our work suggests they will not make a large difference on their own.