COMPETITION BETWEEN AN INTRODUCED AND AN INDIGENOUS SPECIES - THE CASE OF PASPALUM-PASPALODES (MICHX) SCHRIBNER AND AELUROPUS-LITTORALIS (GOUAN) IN THE CAMARGUE (SOUTHERN FRANCE)

Paspalum paspalodes, an introduced grass species, and Aeluropus littor alis, an indigenous species, develop abundantly in seasonally-flooded marshes in the Camargue (Rhone Delta. France), Although they occur tog ether in many multispecies communities, neither species occurs when th e other is dominant. The cultivation of cuttings of P. paspalodes and A. littoralis in a replacement series in a combination of five proport ions (0/100, 25/75, 50/50, 75/25 and 100/0) and four salinities (0, 2, 4, and 6 g Cl- . l-1) gave contrasting results for the two species: ( 1) strong asymmetrical competition in favour of P. paspalodes at 0 g C l- . l-1, (2) no significant effect of salinity on the mean above-grou nd and underground yields per plant for A. littoralis over the range t ested. (3) a major decrease in the mean above-ground and below-ground yields per plant for P. paspalodes with increasing salinity, (4) a rev ersal of the competitive balance between the species with increasing s alinity. The cultivation of cuttings at high temperatures in a greenho use in a combination of the same five proportions at two salinities (0 and 4 g Cl- . l-1) refuted the hypothesis that the introduced species is better adapted to summer temperatures. Because it is not salt-tole rant, P. paspalodes cannot be considered as a potentially invasive spe cies in the Camargue. Its abundance depends on newly created and artif icially maintained habitats.