Ecology of subtropical grasses in temperate pastures: an overview

Subtropical grasses can be a significant component of northern North Island pastures. Several annual and perennial types with different functional characteristics are widely established, allowing a range of different climatic, soil and moisture situations to be colonised. Many of the species have persistent seed banks or vegetative propagation facilitating long-term persistence. Biochemical types associated with moist conditions arc most common but types associated with arid conditions are also represented. Abundant rainfall at temperatures above 25"C, and factors which reduce temperate grass productivity (lowered soil fertility and winter/spring grazing damage) appear to favour higher proportions of both annual and perennial subtropical grasses such as summer grass and paspalum. Grazing pressure and timing, and level of fertiliser inputs appear important for species such as ratstail and carpet grass in less productive sites; The nature of competitive interactions between subtropical (C,) species and temperate (C,) species is poorly understood and invertebrate herbivory can be important in altering the balance between these species. An analysis of present subtropical grass species distributions in northern districts of New Zealand indicates that knowledge of the underlying species biological characteristics is useful in predi'cting subtropical grass abundance. To predict likely problem years and to develop management strategies to minimise problems, a better understanding is needed of the effects of climate on subtropical grass abundance in temperate pastures and competitive interactions. There may be scope for developing improved varieties for dry areas. Keywords: C,, C,, climate, competition, ecology, grazing, pasture, subtropical grasses, temperate