Effects of Microsite Conditions on Seedling Emergence at Grazed and Ungrazed Sites in Mountain Pampean Grasslands, Argentina

Abstract

Seed germination and seedling establishment are the most critical period in many plant species. Plant diversity would be reflected according to the balance between seed bank composition and safe sites availability. In Pampean grasslands of Argentina, plant diversity is threatened by the advance of agriculture, being most of the original grasslands lost. In this context, is increasingly important to know the mechanisms involved in plant diversity maintainance. Seedling emergence would be partly responsible of plants diversity and it may be determined by microsites conditions (competition level, ground cover, presence of disturbances). Here we analyzed (1) the effect of above and below-ground competition and litter application on seedling emergence in non-grazed areas, and (2) the effect of cover of vegetation, litter or dung, bare ground, and soil removal on seedling emergence in grazed areas. In an exclosure and a grazed area, different microsites were created and natural seedling emergence was registered for two years. Above and below-ground competition reduced grasses emergence in non-grazed conditions, but did not affect forb emergence. Litter has no effect on emergence, although it reduced grasses survival. In the grazed areas, soil disturbance has a positive effect on emergence of seedling of all vegetation types, while litter application has a positive effect on grasses emergence. However, survival in this area was very low (<10%). Competition reduced seedling emergence, showing to be a major control factor for the regeneration of the dominant species in the non-grazed areas. Litter presence reduced survival of grasses, but not of forbs. In grazed areas, presence of litter improved microsites conditions, increasing grass emergence. While soil removal increased emergence of seedlings of all vegetation types, probably by favoring root development. In natural grasslands, availability of safe sites has an important role in the establishment of new individuals and regeneration.