Soil phytoliths as evidence for species replacement in grazed rangelands of central Argentina

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 tennis) 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. tennis, 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.