Iglesias, R. M. 2004. Soil phytoliths as evidence for species replacement in grazed rangelands of central Argentina. Á/ Ecography 27: 725 Á/732.Rangeland utilization for livestock production in central Argentina has apparently resulted in the replacement of preferred mid-grasses (Poa ligularis and Stipa clarazii ) by preferred short-grasses (Piptochaetium napostaense and Stipa tenuis ) and avoided grasses (Stipa tenuissima and Stipa eriostachya ). However, the botanical composition in the pristine condition is unknown due to the lack of historical data and relict areas. The objective of this study was to analyze soil phytolith assemblages from a representative site of central Argentina rangelands to test the presumed floristic changes. Soil phytolith assemblages (SPAs) were compared with three plant phytolith assemblages (PPAs), each of it made up of two species. One PPA was integrated by the preferred mid-grasses P. ligularis and S. clarazii , another by the preferred short-grasses P. napostaense and S. tenuis, and a third one by the avoided grasses S. eriostachya and S. tenuissima . For each PPA, the proportion of species representing the best fit with SPAs was estimated by considering all possible lineal combinations between the phytolith assemblage of the two integrating species, and selecting that representing the minimum distance to SPA. The highest degree of similarity between SPAs and PPAs corresponded to the PPA integrated by P. ligularis and S. clarazii . Our results support the hypothesis of the dominance of preferred mid-grasses in the pristine condition in rangelands of central Argentina, and that a shift towards the dominance of preferred short-grasses and avoided grasses has occurred in its present disturbed condition.L. Gallego, R. A. Distel

When formulated in mathematical terms, the problem of zoning a protected natural area subject to both box and spatial constraints results in a combinatorial optimization problem belonging to the NP‐hard class. This fact and the usual dimension of the problem (regularly in the tens of thousands order) suggest the need to apply a heuristic approach. In this contribution we describe a quantitative method for zoning protected natural areas based on a simulated annealing algorithm. Building upon previous work by Bos (1993), we introduce three main innovations (a quadratic function of distance between land units, a non‐symmetric matrix of compatibilities among uses, and a spatial connection constraint) that make the approach applicable for ecological purposes. When applied to solving small‐size simulated problems, the results were indistinguishable from those obtained via an exact, enumerative method. A coarse‐scale zoning of Talampaya National Park (Argentina) rendered maps remarkably similar to those produced by subject area experts using a non‐quantitative consensus‐seeking approach. Results are encouraging and show particular potential for the periodical update of zoning of protected natural areas. Such a capability is crucial for application in developing countries where both human and financial resources are usually scarce but still critical for updating zoning and management plans.

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