Vegetation Change and Ecological Processes in Alpine and Subalpine Sphagnum Bogs of the Bogong High Plains, Victoria, Australia

Abstract

Sphagnum bogs that were monitored over a 15-yr period showed significant changes in the abundance of diagnostic species. At plots ungrazed by cattle, the major bog species Sphagnum cristatum, Caltha introloba, and Carex gaudichaudiana increased significantly in cover. No such increases occurred in grazed plots. There were few changes in cover of the main structural vegetation types—closed heathland, low open heathland, and open herbfield on stony pavements. Sphagnum and the main herbfield species, Oreobolus pumilio and Caltha introloba, were dislodged and shifted over unvegetated stony pavements by snowmelt runoff, snowpack movement, and cattle trampling. Experiments using Sphagnum transplants showed this species capable of colonizing pavements by establishing on other plants. Survival and growth of transplants were significantly greater on low compared with high water flow (high energy) sites. Grazing and trampling by cattle significantly reduced survival of transplants, thus disrupting the colonization of pavements; firstly, by directly reducing the survival and growth of Sphagnum and other colonists; and secondly, by preventing the formation of barriers to water flow that would facilitate colonization. We propose a successional dynamic based on some of the processes operating in the open herbfield and stony pavements of Sphagnum bogs.