Changes in the Quantitative Floristics in Some Astrebla Spp. (Mitchell Grass) Communities in South-Western Queensland in Relation to Trends in Seasonal Rainfall

Abstract

Seasonal changes in the quantitative floristics at a wide range of Astrebla grassland sites in south-western Queensland were monitored between 1972 and 1980 with a wheel point apparatus. Changes in the floristics were measured in terms of both relative abundance and basal cover. A large increase in the relative abundance of perennial grasses, particularly Aristida latifolia, Astrebla spp. and Dichanthium sericeum, occurred between 1972 and 1976. This increase was at the expense of annual grasses and forbs which declined in both relative abundance and number of genera present. The relative abundance of perennial grasses declined between 1978 and 1980 and this was associated with a large increase in the forbs such as Daucus glochidiatus and Plantago spp., particularly at southern sites. The contribution of annual grasses to botanical composition remained low throughout the period. Total basal cover differed between years although these differences were not significant. As perennial grass, particularly Astrebla spp., was the major vegetation component of total basal cover, changes in the latter were associated mainly with changes in the basal cover of Astrebla spp. Changes in the contribution of individual species to total basal cover were related to changes in the relative abundance of those species. Changes in botanical composition in Astrebla grassland may be influenced more by trends in seasonal rainfall than by grazing pressure.

Managed livestock grazing is compatible with the maintenance of plant diversity in semidesert grasslands

“…Aristida latifolia has previously been recognized to indicate the early stages of degradation (Phelps and Bosch 2002), but this perspective may reflect its perception as a pest with seeds that irritate sheep and taint wool . Substantial increases in the relative abundance of Dichanthium sericeum occur in the Mitchell grassland during periods of above average rainfall (Orr 1981, Orr Notes: Life-form abbreviations are: AG, annual grass; AH, annual herb; PG, perennial grass; and PH, perennial herb. Evidence of grazing response was taken from the following studies: 1, Orr (1980); 2, Foran and Bastin (1984); 3, Orr and Evenson (1984); 4, Dorrough et al (2011);5, Fensham et al (1999); 6, Fensham and Skull (1999); 7, Phelps and Bosch (2002);8, McIntyre et al (2003); and 9, Lewis et al (2008).…”

Quantitative floristics as a tool for the assessment of plant diversity in Tuscan forests

“…Herbst and Roberts, 1974;Orr, 1981), these techniques are scarcely used for management and monitoring practices. Most of the evaluation and monitoring activities related to large area are limited to the repeated sampling of relatively small, or circumscribed, stands.…”

Guilds, Functional Types and Ecological Groups

“…Use Callaway and Sabraw (1994) demonstrated that, on a Californian saltmarsh, one plant species was abundant in wet years but completely absent in dry years, whilst another species showed the reverse pattern; Gutierrez et al (1993) gave evidence that, in arid scrub in Chile, some annual species were present in some years but not in others, depending on the weather; and Orr (1981) identified plant species that were more abundant at a site in wet years. If the timescale of the variation were larger than the lifespan of the individuals, different guilds could occupy different time niches, e.g.…”