Multiscale Indicators of Land Degradation in the Patagonian Monte, Argentina MO ´ NICA B. BERTILLER* JORGE O. ARES ALEJANDRO J. BISIGATO Centro Nacional Patago ´ nico-CONICET Boulevard Brown s/n 9120 Puerto Madryn Chubut, Argentina ABSTRACT / Depletion of vegetation by overgrazing in arid envi- ronments has long-lasting effects on the environmental quality over extended geographic areas. An adequate inspection of hab- itat changes requires scaled up procedures that would allow as- sessing end-points of environmental status in broad areas that would be based on processes occurring at the plant canopy level. Our purpose was to find indicators of land degradation– conservation status for use in land monitoring programs and in planning management practices that would be amenable to fur- ther up-scaling for use with remotely sensed imagery. In several sites of the Patagonian Monte differing in the impact of grazing management, we evaluated vegetation attributes at three spatial scales. At the population scale, we found that the severity of grazing impact was characterized by the reduction of the palat- able grass, P. ligularis, outside and inside shrub canopies. At the vegetation patch scale, we found that land degradation by do- mestic herbivore impact was characterized by changes in at- tributes of patch shape (radius, height, internal canopy cover) and patch abundance. At the plant community scale, we found that the structure of the plant canopy as described using Fourier analysis of cover data changed after long-term grazing impact consistently with the modifications in plant population and patch structures. We present a conceptual multiscale scenario of struc- tural changes triggered by domestic herbivore impact, and quan- titative indicators of plant structure and processes useful to de- velop management strategies of the Patagonian-Monte that would conserve its natural habitats. The developed end-points are also amenable for use in land conservation assessment through remotely sensed imagery. The development of analytical tools to study the effects of land uses on the distribution, abundance, and interactions of organisms is an important applied eco- logical issue (Gardner and others 1993) that preferably should be analyzed by multiscaled and hierarchical approaches (Rahel 1990, Gardner and others 1993, Ryerson and Parmenter 2001). Herbivores produce im- portant environmental impacts, such as reducing the populations of high-valued plant species, facilitating the invasion of shrubs (Schlesinger and others 1990, Milchunas and Lauenroth 1993), and changing the patterns and scale of the vegetation spatial heterogene- ity, soil resources, and terrestrial microenvironments (Bertiller and Coronato 1994, Callaway 1995, Bertiller 1996, 1998, Schlesinger and others 1996, Wilson 1998, Bertiller and Bisigato 1998, Mazzarino and others 1998, Adler and others 2001). All these produce changes in ecosystem functions such as primary productivity and nutrient cycling (Bolton and others 1990, Schlesinger and others 1990, Ludwig and Tongway 1995). The Patagonian Monte occupies an area of about 42,000 km 2 in northeastern Chubut Province (Figure 1). As in the rest of Patagonia, domestic herbivores (sheep) were introduced in this area at the beginning of the last century (Soriano 1983, Ares and others 1990) and are nowadays the predominant herbivores. Lama guanicoe (guanaco), the only known wild ungulate species, is still widely distributed in the region at small local populations. Several evidences indicate that the populations of guanaco underwent a strong decline after the introduction of domestic sheep. Baldi and others (2001) recently found that sheep densities may be 23 times higher than sympatric guanaco densities and that sheep monopolize the most productive land areas. The assessment of the environmental impact of domestic herbivores in the Patagonian Monte at a spa- tial scale that would be useful to define land conserva- tion end points has been largely based on botanical changes at a high resolution spatial scale. However, overgrazing and soil erosion are extended processes that result from the spatial patterns of sheep impact and their temporal distribution (Ares and others 1990, Defosse ´ and others 1992, Bertiller 1996). Sheep herds are kept all year round in relatively large contiguous paddocks or management units (25 km 2 or more), sharing a single watering place (Defosse ´ and others 1992). As a consequence of the location of the watering points, site topography, and foraging behavior (Stuth KEY WORDS: Arid lands; Herbivore impact; Habitat fragmentation; Fou- rier spectral analysis *Author to whom correspondence should be addressed; email: bertil@cenpat.edu.ar DOI: 10.1007/s00267-002-2725-4 Environmental Management Vol. 30, No. 5, pp. 704 –715 © 2002 Springer-Verlag New York Inc.