Grazing effects on patchy dryland vegetation in northern Patagonia.

BISIGATO, A.J.; BERTILLER, M.B

JOURNAL OF ARID ENVIRONMENTS

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Manchester; Año: 1997 vol. 36 p. 639 - 653

0140-1963

In this study the spatial patterns and dynamics of vegetation patches along agrazing gradient in the steppe of Larrea divaricata and Stipa spp. in NEPatagonia (Argentina) are described. A general effect of grazing is thereduction of total plant cover resulting from the decrease in cover of perennialgrasses (Stipa speciosa, Poa ligularis, Stipa tenuis) and some tall shrubs(Chuquiraga hystrix, Bougainvillea spinosa, Lycium chilense). Dwarf shrubs(Nassauvia fueguiana and Junellia seriphioides) increase their cover undermedium and/or high grazing pressures. Plant species are spatially groupedinto patches which alternate with areas of bare soil. Eleven types of vegetationpatch differing in the dominant plant functional type or species, floristicrichness and size were identified with different relative frequency along thegrazing gradient. Based on these results, it is postulated that grazing forces thereplacement of large patches dominated by tall shrubs with high speciesrichness, by Larrea divaricata patches or small dwarf shrub patches with lowspecies richness and the extinction of grass patches. This results from: (1)disruption of local balances of species deletions and additions; (2) fragmentation of large patches; and (3) formation of new vegetation patches. Thesechanges lead to differing plant spatial organization and heterogeneity alongthe grazing gradient which may be described by characteristic arrays ofvegetation patches.©1997 Academic Press LimitedKeywords: patch patterns; patch dynamics; recolonization; fragmentation