SEEDLING DYNAMICS OF FESTUCA SPP IN A GRASSLAND OF PATAGONIA, ARGENTINA, AS AFFECTED BY COMPETITION, MICROSITES, AND GRAZING

The effects of competition, grazing, and microsites on seedling dynami cs of Festuca spp. were investigated in a semiarid steppe of Patagonia , Argentina. In an exclosure and an adjacent grazed area, the level of root competition for seedlings was controlled through root exclusion tubes (0.1 m diameter, 0.4 m long) installed adjacent to 7 similarly-s ized Festuca pallescens plants and in the interspace between F. palles cens plants. Seedling dynamics at the phenological stages of a) recent ly emerged and up to 4 leaves and b) 5 leaves and up to 1 tiller were followed inside the tube area (no competition) and in paired circles ( competition) for approximately 3 growing seasons. Peak density of Fest uca spp. seedlings occurred in fall and early spring, when water conte nt in the first 0 to 5 cm of the soil was above 8%. Seedling densities of Festuca spp. at the 2 phenological stages were significantly reduc ed by grazing. At the phenological stage of 1 to 4 leaves, seedlings w ere not affected by root competition, although their densities were si gnificantly higher for seedlings adjacent to F. pallescens plants than in the interspace between plants. This was due to higher soil water c ontent in these areas throughout the season in the 0 to 5 cm of the so il. Seedling densities at the phenological stage of 5 leaves and up to 1 tiller were significantly higher when there was no competition from neighboring grass plants as compared to seedlings exposed to competit ion, In regard to microsite differences, seedling density was signific antly greater in the interspaces than adjacent to mature plants. These results suggest that although higher seedling densities can be obtain ed by excluding the area from grazing, intraspecific competition for s oil water during the summer drought period can act as a barrier for fu rther Festuca spp. seedling establishment.