Environmental relationships and ecological responses of some higher plant species on rock cliffs in northern Tasmania.

Abstract Gravity, moisture availability and shade exert a major control over the distributions of vascular plant species on sandstone cliffs in the Great Western Tiers, northern Tasmania. The vegetation is dominated by ferns, some of which are almost always restricted to cliffs, with invasion of shrub and tree species where soil has been able to accumulate. Although it might be expected that species commonly found over a wide range of vegetation types could displace obligate cliff dwellers, this potential is rarely fulfilled. The vertical nature of the environment precludes the loss of cliff obligates, as soil-vegetation mats peel off in part of a truncated and cyclic successional process. Experimental work and field monitoring of growth and mortality in single species and mixed stands showed that the cliff obligate fern Blechnum uulcanicum (Blume) Kuhn is slower growing, more drought resistant and less responsive to fertilizer than its non-obligate associate, B. umttsii Tind.