Population Dynamics of Two Perennial Grasses in Australian Semi-Arid Grassland

Abstract

Plant ecologists have expended much effort in counting, charting, cutting, drying, weighing and photographing vegetation. To date these labours have contributed little to our knowledge of the population biology of plant species. Indeed, Harper (1967) has written 'of a demography which has never gained a momentum in plant ecology, although it has played a vertebral role in animal ecology'. This paper presents a demographic treatment of density data acquired between 1949 and 1965 for Danthonia cespitosa Gaudich. and Chloris acicularis Lindl., two indigenous perennial grasses of differing ecological status in grazed and protected (ungrazed) semi-arid grassland near Deniliquin (35? 32' S, 144? 58' E), New South Wales, Australia. From these data the survival patterns of the grass populations are determined, and compared. Danthonia cespitosa is the dominant grass in the community, and Chloris acicularis is a sparsely distributed tussock-grass, the sole survivor in grazed situations of a group of summer-growing grass species that were widespread and locally abundant before European settlers introduced sheep and cattle in the mid-nineteenth century (Moore 1962). The difference in phenology between the two grasses is marked. Danthonia cespitosa is an opportunist in its vegetative growth, responding to rain in all seasons, whereas Chloris acicularis is dormant in winter and depends on effective summer rain for both vegetative and reproductive growth.