Seasonal variation in the seed bank of a Patagonian grassland in relation to grazing and topography

BERTILLER, MÓNICA B.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 1992 vol. 3 p. 47 - 54

1100-9233

The germinable seed bank of Festuca spp., Carexpatagonica, and other annuals and perennials in a semiaridPatagonian grassland was analyzed every three months. Theeffects of grazing, topography and microsites with respect toestablished grass tussocks on the germinable-seed bank werealso analyzed. The total germinable-seed bank was larger insummer after seed rain. At this time of the year most of theseeds were from annuals and perennial dicots. Seeds of thedominant Festuca spp. were the main components of thegraminoid seed bank, which was homogeneously distributedin patches of bare soil. In spring, i.e. some months after theseed rain, the germinable-seed bank of most of the species wasgreatly reduced, while the seed bank of Carex patagonica didnot change significantly. At this time of the year, the graminoidseed bank was heterogeneously distributed in space, with theseeds accumulating in wind-protected microsites. In the grazing treatments, the seed bank of the perennial grasses wasreduced proportionally to the decrease of the plant cover. Onthe other hand, the germinable-seed bank of C. patagonicaincreased with the grazing treatments, in relation to the increase of vegetation cover.Topographical position had two types of effect on the seedbank of perennial grasses. One was the increase of thegerminable-seed bank, after the seed rain, on the relativelywarmer northeast facing slopes, which was related to a higherseed rain in these places. The other was an increased seed losson slopes.The different seed-bank strategies observed in this grassland are compared and discussed in relation to strategiesdescribed for other grasslands.