Potential steelhead over-summering habitat in the south-central/southern California coast recovery domain maps based on the envelope method

Recovery efforts for steelhead are likely to be aided by maps of potential habitat. In the South-Central/Southern California Coast recovery domain, the most geographically restricted habitat type is probably oversummering habitat, due to the Mediterranean climate and the general aridity of the region. Here we develop a model of potential oversummering habitat and map it in a Geographic Information System, using the method of environmental envelopes. Under the envelope method, predicted habitat is the set of stream segments falling within the same range of conditions that encapsulate the known occurrences of the species. Thus the method is based on known occurrences described in museum records, environmental reports, scientific papers, and other credible sources. The axes for the "range of conditions" are geomorphic, hydrologic, and climatic features thought to control the broad-scale suitability of stream reaches under natural (unmanaged, unimpaired) conditions. The specific predictors for potential habitat were stream gradient, summer mean discharge, summer temperature, valley width relative to mean discharge, and whether or not the reach occurred in alluvial soils. The resulting model predicts over-summering habitat throughout the recovery domain, as illustrated in 10 synoptic maps included in this report. Various limitations of the model are described at length. David A. Boughton, Matthew Goslin. "July 2006." System requirements: Adobe Acrobat Reader. Mode of access: World Wide Web. Includes bibliographical references (p. 32-34).