SELECTION FOR GRASSES WITH DIFFERENT CARBON ASSIMILATION PATHWAYS UNDER DIFFERENT SHEEP STOCKING PRESSURES

The path of carbon assimilation was noted for 30 common grasses from u nfertilised sheep pastures of the Northern Tablelands of New South Wal es. These grasses were then grouped according to their susceptibility to stocking pressure and the frequency and relative frequency of 16 of these related to apparent intensity of stocking about a sheep camp. C 3 grass frequency was independent of stocking pressure, but under heav y stocking introduced C3 species replaced native C3 species. C4 NADME species showed an increase in occurrence under high stocking rates, wh ereas C4 NADPME species showed a decrease in occurrence under high sto cking intensity. Response to grazing may have been a factor in the evo lution of different pathways of carbon assimilation.