The need of improve the definition of "Fragmentation": Habitat models as a tool

VERÓNICA, RUSCH; MARÍA VICTORIA, LANTSCHNER

San Carlos de Bariloche, Argentina

Workshop; Workshop on Forest Fragmentation in South America; 2006

Cemagref (Francia) y Centro Regional Universitario Bariloche, Universidad Nacional del Comahue

Landscape or forest fragmentation is an ambiguous term, it is tightly related to the organism or community you are looking at, and also to the scale and the process considered (Haila, 2002; Wiegand et al., 2005). To define fragmentation we should define precisely the focal objectives of conservation. To exemplify the concept we developed and habitat model for a bird species, Scelorchilus rubecula (chucao), and compared it to habitat requirements of Campephilus magellanicus (magellanic woodpecker) previously defined for Forest Management Plans (Marqués et al., 2000). Both species are typical of Andean Patagonic Forests in SW Argentina. To construct the habitat model we employed data of presence and absence in 98 sites (6 to 8 census in each site) recorded in different types of Nothofagus forests and shrublands, Austrocedrus chilensis forests, steppes, humid grasslands, and exotic forest plantations. For each site, variables as composition and coverage of each vegetation species were registered, as well as other variables as altitude, exposition, latitude and longitude (precipitation). Concentric circles of 500, 1000 and 2000 m around each site where drawn on vegetation maps determining landscape indexes through Patch Analysis software (ESRI, 1996). A logistic model was constructed. Shrub cover was the most important variable to predict chucao?s presence, while bamboo (Chusquea spp.) presence sharply increased the probability of finding the species. This information, together with the knowledge of the low dispersion capability of the chucao, determines that connectivity of its habitat should be defined through the continuity of a dense shrub strata or the presence of the bamboo. On the other side, the magellanic woodpecker needs mainly mature Nothofagus spp. trees, but the capability of flying up to 5 km can also transform a landscape composed by forest patches in a continuous forests for these individuals, as open areas are not barriers for the species. This shows that a clarification of the term in relation to an objective or species considered is needed. Another important issue is that, when landscape use has to be planed, the difference of natural or anthropogenic causes should be determined. In many opportunities, the heterogeneity of the resources availability (e.g. nutrients, water, vegetation) or other environmental conditions (e.g. radiation, temperature) predetermines a ?natural fragmented landscape pattern? where different kind of disturbances can interact. Nevertheless this is not always taken onto account when the levels of fragmentation of a region are established.