330 ##?$aThe effect of sward state and stocking rate upon leaf growth, senescence and consumption rates per tiller and upon the efficiency of herbage utilization in Lolium multiflorum (C3 annual grass), Paspalum dilatatum and Cynodon dactylon (C4 perennial grasses) within a native grassland continuously grazed by cattle under natural mineral and hydrie conditions was analyzed. Data of two complementary studies, one on leaf morphogenesis and the other on the effect of N fertilization on the dynarnics of herbage growth and utilization, are also presehted. Results demonstrated that leaf length (LL) and number of living leaves (NLL) per tiller can be adequately predicted by the association between leaf morphogenesis dynamics and temperature. However, canopy structure modified leaf appearance as weil as LL and NLL, the consideration of this plastic response being postulated as central to extend morphogenetic models of leaf growth to field conditions. Growth and senescence rates were generally not linked along the experimental cycle, this phenomena being particularly marked in the C4 grasses. The importance of such dynamics to optirnize the defoliation regime in complex plant communities under fluctuating temperatures is discussed. Results confirm that while the probability of defoliation (PDf) during the leaf life span (LLS) depends on stocking rate, the intensity of each defoliation is relatively constant. This supports that PDf and LLS constitute the main components that define the leaf proportion that will senesce and, hence, the efficiency of herbage utilization. Species selectivity analysis suggests that defoliation pattern results can be general to a wide range of species abundance. Evidences are presented on the positive effect of herbage growth increase upon the carrying capacity and the efficiency of herbage utilization. On this basis, the role of LAI and stocking rate as determinants of leaf tissue flows dynamics under continuous grazing are discussed.