Does land conservation reduce the local housing supply?

An aerial view of housing developments near Markham, Ontario Photo by IDuke.A new study wades into the contentious debate about whether land protection negatively affects the housing supply for local communities.

Pro-development advocates have argued that land conservation removes properties from the pool of potential residential housing and therefore drives up home prices. Some studies have found empirical support for this argument.

However new research from scientists at Stanford University and the Nature Conservancy finds that conservation efforts in the suburbs of the San Francisco Bay Area have only had a modest effect on reducing the available housing supply.

Carrie Denning and fellow researchers conducted spatial analysis to estimate how many houses would have been developed in the Silicon Valley area had conserved lands never been protected.

To explore this hypothetical scenario, they first created a model to explain how current development patterns relate to seven variables: slope, wetland status, distance to stream, distance to highways, distance to railroads, and the distance to historical urban centers. They then applied that model to conserved lands to estimate the expected level of development on these properties had they never been protected.

The researchers calculated that 51,000 additional houses would have been built which equals about 6.5% of the 790,000 houses currently in Silicon Valley. They estimate that the average housing density of this added stock would be very low at 1.1 houses/hectare compared to the 4.2 houses/hectare currently developed in Silicon Valley.

This is because the protected lands are largely poor prospects for housing development. According to the study results, steep slopes and proximity to streams and wetlands limit the development of many of these properties. The conserved lands with the highest estimated densities include urban parks that were primarily protected to provide amenities for subdivisions. Excluding these urban parks, the density and total development estimates of conserved lands would obviously be even lower.

Despite the poor development potential of these properties, the authors argue that protecting these lands has been beneficial for conservation. Many of these properties contain important habitat and provide valuable ecosystem services. Even low-density development would have threatened these values, and as the study results show, overall increases to the housing supply would have been modest.

--Reviewed by Rob Goldstein

Denning, C., Mcdonald, R., & Christensen, J. (2010). Did land protection in Silicon Valley reduce the housing stock? Biological Conservation DOI: 10.1016/j.biocon.2010.01.025