Fire and survival of Stylosanthes spp. in the dry savanna woodlands of the Northern Territory

Abstract

A series of burns was carried out during the early and late, dry season and early wet season, in mixed native grass-legume plots containing Stylosanthes humilis, S. hamata, S, scabra and S. viscosa as the legume component. The least mortality was shown by S. scabra, but its survival was poor in any sward more than 3 years old. After burning the other species relied solely on seedling regeneration for subsequent season's growth. Fire killed a considerable quantity of seed, but its heat softened hard seed in the soil and good germination occurred with summer rains. However, the presence of a large proportion of soft seed through the winter months could lead to out-of-season germination and subsequent death of seedlings after unseasonal winter rains. Although the total dry matter yield of swards was reduced by all fires, burning could play an important part in increasing yields of S. hamata in swards overgrown by dense native grass, since it increases the amount of soft seed in the soil. If burning causes a high mortality of mature plants of the perennials S. scabra and S. viscosa, a reduction in stocking rate may be needed to ensure regeneration of a productive sward, as these species have slow seedling growth rates.