Requirement of vegetation gaps for seedling establishment of two unpalatable grasses in a native grassland of central Argentina

MORETTO, A. ; R. DISTEL

Australian Journal of Ecology

Blackwell Publishing

Año: 1998 vol. 23 p. 419 - 423

0307-692X

The objective was to determine the effects of root and shoot competition on seedling establishment of the unpalatable grasses Stipa gynerioides and S. tenuissima in the native grassland of central Argentina dominated by the palatable grass S. clarazii. Seeds of two unpalatable species were sown in natural occurring microsites with shoot and root competition from the palatable species, and the artificially created microsites without either shoot competition or shoot and root competition. In addition, fresh seeds of the unpalatable species were subjected to daily alternating temperatures under laboratory and fiel conditions to determine the effects on seed dormancy and germination. Seedling establishment of S. gynerioides and S. tenuissima occurred only in microsites without shoot and root competition. Also, the fluctuation of temperature near the soil surface in these microsites reduced dormancy and promoted rapid germination in both species. Our results support the hypothesis that, in swards dominated by palatable grasses, vegetation gaps of low competitive pressure favour seedling establishment of unpalatable grasses. It is suggested that the creation of these gaps by overgrazing can be an important mechanism in the process of species replacement in native grasslands.