The biological diversity that is supported by a particular area is generally a positive function of the degree of environmental heterogeneity occurring over space and time within that area. Because heterogeneity or patchiness can occur from very small to very large spatial scales, biodiversity, at the extensive scales covered by landscapes can be affected by heterogeneity occurring in a nested series of smaller-scale patches. We discuss this relationship between patchiness and biodiversity in the context of nonequilibrium models of community organization, such as source/sink and metapopulation models, and contrast this with the traditional equilibrium view of ecological communities. We provide empirical examples from western Great Basin landscapes demonstrating that animal species diversity is a positive function of heterogeneity in the local vegetation. We then extend this to consider stand renewal processes in Great Basin plant communities, especially effects of anthropogenic changes in these processes on landscape-level heterogeneity. Under pristine conditions small-scale and infrequent herbivory may have been the predominant mechanism of stand renewal, but this process has been overshadowed during this century by large-scale, catastrophic fires. A promiscuous burning period in which fires were intentionally set characterized stand renewal shortly after European settlement of the West. For the past several decades this has been replaced by frequent unintentional range fires carried by fine fuels provided by introduced annual weeds. These changes in the spatial and temporal patterns of stand renewal reduce environmental patchiness and associated biodiversity across Great Basin landscapes.
Longland, William S. and Young, James A.
"Landscape diversity in the western Great Basin,"
Natural Resources and Environmental Issues:
Vol. 4, Article 9.
Available at: http://digitalcommons.usu.edu/nrei/vol4/iss1/9