Modeling urban land development as a continuum to address fine-grained habitat heterogeneity

Natural landscapes are increasingly subjected to impacts associated with urbanization, resulting in loss and degradation of native ecosystems and biodiversity. Traditional classification approaches to the characterization of urbanization may prove inadequate in some human-modified landscapes where complex and unique combinations of conditions can make classification and delineation of patches difficult. We describe a model that depicts existing human development as a fine-grained continuous variable using parcel-based land use data and transportation networks. We derived percent development values across our 88 000-ha study area, the Lake Tahoe basin. Our modeled values were highly correlated with observed levels of development based on high-resolution aerial photographs. We demonstrate how our model of development can be used to address practical conservation questions by evaluating the potential effects of highly interspersed urban land development and wildland conditions on the amount and availability of habitat suitable for the resident California spotted owl (Strix occidentalis occidentalis) at two points in time (current and 40 years in the future). The results indicated that assessments not accounting for the indirect effects of development may overestimate the amount of available habitat by 19-83%. Portraying urbanization as a continuum across entire landscapes captured fine-grained landscape complexity at scales that were relevant to the habitat needs and environmental sensitivities of a species of conservation interest. This relatively simple approach should aid ecologists and landscape planners in evaluating the current or future effects of urbanization on ecological elements and processes.