Patch mosaic cyclic succession associated with the growth and senescence of an alpine shrub

Abstract

Endogenously-induced cyclic vegetation change has been associated with the life cycle of shrub species, resulting in mosaic or linear patterning in vegetation. We investigated whether mosaic cyclic succession was taking place in Richea acerosa (Lindley) F.Muell. alpine heath on the Central Plateau of Tasmania, Australia by determining the variation in species composition associated with different growth characteristics of the shrub and by monitoring shrubs in plots over 11 years. Temperatures below and adjacent to shrubs were measured in clear sky conditions to determine if microclimatic variation was associated with structural and floristic variation. Species richness was higher outside than inside the shrubs, and was further depressed by an increasing proportion of dead material in the shrub. However, Poa saxicola R.Br. appeared to be protected by the prickly foliage of R. acerosa and also preferentially occurred among the mass of dead stems that characterised the centre of older plants. There was a strong floristic shift associated with the development of the shrub. The live cover of individual shrubs remained constant in all plots over the 11 years, while plots initially dominated by senescent plants contained young plants and vice-versa. The live part of the shrubs moderated temperatures. However, root competition and protection from grazing seem likely to have made a major contribution to the shifting conditions associated with the mosaic cyclic succession.