A Technique for Assessing Land Surface Ruggedness

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Land surface is a vital component of habitat for many wildlife species. Obvious examples include mountain goats (Oreamnos americanus) and peregrine falcons (Falco peregrinus) that generally occupy precipitous terrain for at least part of the year. In contrast, pronghorn (Antilocapra americana) and greater prairie-chicken (Tympanuchus cupido) occupy level to gently rolling Kramer (1972) suggested that terrain may be 1 means by which mule (Odocoileus hemionus) and white-tailed deer (0. virginianus) partition habitats in areas where the 2 species are sympatric. There may be a threshold of beyond which the habitat becomes increasingly less suitable for a particular taxon. Therefore, quantification of may be important when evaluating habitat quality or use. Previously (Russo 1965, Wood et al. 1970, Snow 1972), where has been implicated as a key component of an animal's habitat, investigators have qualified it as precipitous, mountainous, or rugged. Although descriptive, such assessments preclude statistical treatments of data because the amount of among locations is not quantified. Koerth (1981) attempted to quantify habitat for mule deer by measuring average degree of slope occupied by individual animals. This approach provides an assessment only at individual sites, however, and does not describe the overall terrain of an area. Geomorphologists have attempted to index the of drainage basins by (1) calculating total relief (maximum minus minimum elevation) (Schumm 1956); (2) calculating a dimensionless ruggedness number (HD) that is the product of total relief (H) and drainage density (D), or total length of all streams per unit of area (Melton 1957); or (3) conducting a hypsometric analysis that shows the relationship between horizontal cross-sectional drainage basin area and elevation (Strahler 1952). However, these methods similarly fail to quantify the myriad of slopes, draws, peaks, aspects, and elevation changes that collectively comprise rugged terrain. There appears to be no method presently available that provides an objective quantification of this complex habitat characteristic. The objective of this investigation was to develop a method to quantify topographic as a feature of an animal's habitat.