Small‐scale plant dynamics in temperate Themeda triandra grasslands of southeastern Australia

Abstract

Abstract. Vegetation subjected to two long‐term burning regimes (annual or biennial burning) was studied in permanent plots, at two spatial scales: 0.01 m2 and 1 m2, to determine the small‐scale dynamics of plants in temperate Themeda triandra grasslands of southeastern Australia. Species turnover rates were estimated by presence/absence data while species mobility was assessed using cumulative frequency data.While mean species richness did not fluctuate greatly between years, the vegetation was internally dynamic rather than static. Cumulative species richness increased by 50% at both spatial scales and sites over the 4‐yr study period. However, few species became cumulatively frequent (i.e. occurred in 80% of plots in the first and/or subsequent years), suggesting that cumulative species richness increases were due to small‐ or local‐scale movements of plants, rather than ‘shifting clouds’ of species moving across the entire site. The vegetation's dynamics did not differ greatly at sites subject to different (frequent) fire intervals.Species turnover and mobility were individualistic, but the dynamics of many species was greater at the smaller spatial scale: 31–48% of the species present at both spatial scales at the two sites had higher turnover rates at the 0.01 m2 scale. Similarly, some ‘non‐mobile’ species at the 1‐m2 scale (i.e. ‘constant’ or ‘local’ mobility types), were more mobile at the smaller‐scale. Turnover rate and mobility type were strongly associated with life form in some cases, particularly at the annually‐burnt site. In general, therophytes (and to a lesser degree, geophytes) were positively associated with high turnover and mobility in most years, while hemicryptophytes were negatively associated with high turnover in many instances. Hemicryptophytes included many species with a range of mobility types and hence, few significant associations between mobility and this life form were found.The previously unrecognized internal dynamics of this community under ‘stable’ management regimes contributes to species coexistence by allowing plants with different dynamics properties to persist in a spatially and temporally unpredictable manner. Frequent burning is presumably the important component driving much of the non‐directional, small‐scale dynamics because it regularly destroys individual plants and aerial plant parts and creates opportunities for seedling regeneration, whilst permitting the vegetative persistence and spread of established plants in non‐light‐limited microsites.