As. Moretto et Ra. Distel, COMPETITIVE INTERACTIONS BETWEEN PALATABLE AND UNPALATABLE GRASSES NATIVE TO A TEMPERATE SEMIARID GRASSLAND OF ARGENTINA, Plant ecology, 130(2), 1997, pp. 155-161
The argument that selective grazing leads to competitive replacement o
f palatable grasses by unpalatable grasses is based upon the assumptio
n that the competitive ability of the palatable species is higher than
the one of unpalatable species in the absence of grazing. In order to
test this hypothesis we have compared the competitive ability of Stip
a clarazii (palatable) and S. trichotoma (unpalatable) under held cond
itions, and S. clarazii and S. gynerioides (unpalatable) under greenho
use conditions. The three species are native to a temperate semi-arid
grassland of central Argentina. In the held experiment, plants of both
species were grown either independently or in pairs (palatable + unpa
latable), protected from grazing. Shoot and seed production were measu
red at the end of the growing seasons of 1993, 1994 and 1995. In the g
reenhouse experiment, plants of both species were grown in pots, eithe
r in monoculture or in mixture, under conditions of high and low water
and mineral nutrient availability. Total biomass and seed production
were measured at the end of the experimental period. In both experimen
ts the presence of the unpalatable species did not affect (P > 0.05) t
he productive responses of the palatable species. On the contrary, the
presence of the palatable species significantly reduced (P < 0.05) th
e productive responses of the unpalatable species. Our results support
the assumption, on which most interpretations of floristic changes in
duced by grazing are based, that the competitive ability of palatable
grasses is higher than the one of unpalatable grasses in the absence o
f grazing.