Ecosystem service demand and supply along the urban-to-rural gradient

Abstract

The concept of ecosystem services has gained popularity in conservation biology and conservation planning, as a means to quantify the myriad ways humanity depends on nature. However, research into incorporating ecosystem services into conservation planning has to date focused on ecosystem service supply, where natural resources of interest to people are generated, rather than on ecosystem service demand, where people are consuming them. Here a simple analytical model is presented that describes the effect on conservation planning of distance between ecosystem service supply and demand. An explicit analogy is drawn between classic bid-rent theory in economics, describing the distance of different industries from city centers, and this conservation planning problem. The functional form of classic bid-rent theory is expanded to include site cost and site threat, including the probability of development and the fraction of ecosystem service generation left after development. A set of specific predictions is developed that describe where particular ecosystem services would be optimally protected in an urban region, as a function of the urban rent gradient and ecosystem service demand, transportability, and threat. Evidence is presented from the San Francisco Bay Area testing these predictions. Spatial patterns of land protection by conservation groups aiming to protect different ecosystem services are consistent with model predictions, suggesting the model is a useful conceptual framework for thinking about how to protect ecosystem services along an urban-to-rural gradient.