Antagonistic effects of grazers and shrubs on the emergence and establishment of seedlings in a sub-humid grassland of South America.

Abstract

Biotic interactions are key processes that strongly affect the performance of seedlings in plant communities. In this work, we evaluated the effect of grazing and shrubs on the emergence and establishment of seedlings with different life-forms (dicotyledonous and monocotyledonous) in a sub-humid grassland community. We delimited five areas of 25m2 in which we established four permanent plots of 1.0m2. Two plots were centered at shrubs (beneath the canopy) and two in open spaces (without shrubs). Half of the shrubs and open plots were fenced to avoid grazing. During two consecutive years we marked all emerged seedlings and followed their fate. Grazing promoted dicotyledonous seedling emergence but reduced establishment. On the contrary, shrubs reduced dicotyledonous emergence but enhanced establishment. We did not detect any effect of shrubs or grazing on the emergence of monocotyledonous seedlings. Most seedlings emerged during fall and winter and died during spring and summer. Recruitment from seeds in this grassland is rare and complex, involving biotic and abiotic factors, with different responses to grazing and shrubs depending on seedling life-form and ontogeny.