Revisiting the browsing lawn concept: Evolutionary Interactions or pruning herbivores?

Browsing lawns, as an analogue of the influential grazing lawn concept, received increased recent interest. We revisit this concept and ask whether the underlying characteristics of a grazing lawn can indeed be generalized to browser-woody plant interactions. Based on previous studies, we define a lawn as a grazed or browsed patch in which intense foraging leads to increased resource availability and a proportional increase of palatable plant species in the patch. We then argue that present examples do not fully support a browsing lawn analogue. Although intense browsing can lead to increased resource availability, it generally reduces the share of palatable plant species in the community. We present an example that does seem to fit both lawn conditions; intensely browsed regeneration patches of palatable trees in Bialowieza Primeval forest. Browsing not only prunes these regeneration patches into lawn-like structures, but also increases the share of palatable species in the tree community. Finally, we outline key open issues of the browsing lawn analogue anti discuss the discrepancy between our example and the general understanding that browsing reduces the share of palatable tree species. We suggest that lawns are most likely to develop in relatively resource-rich environments where plants can invest in tolerance traits and in situations where herbivores show strong patch selection but are relatively unselective for individual plants within the patch. Although our example fits these conditions, many studies on browser-woody plant interactions come from relatively nutrient poor systems with strong selection for individual palatable trees. More studies in systems similar to our example might show that positive interactions between browsing and the proportion of palatable woody species in a community are not so rare. (C) 2011 Elsevier GmbH. All rights reserved.