4 - Flora

Summary

Cliffs are largely inaccessible to people and their livestock and are therefore generally free from disturbances such as grazing and fire. As we have already shown, cliffs cannot support organisms with high productivity and therefore most vegetation on cliffs is small and unassuming. We believe that these features are the reasons why cliffs have attracted far less attention from biologists than other more accessible habitats with large numbers of productive macroscopic organisms. Maycock and Fahselt (1992) studied the vegetation of high arctic cliff faces and scree slopes in Canada that had previously been described as ‘unvegetated’. On these surfaces they found 156 plant species, of which half were lichens, one-quarter were macroscopic higher plants and one-quarter were bryophytes. The authors offer no satisfactory explanation as to why others might have so grossly misrepresented the diversity of species in these habitats, but they hint that the appearance of low productivity has discouraged close scrutiny in the past. The same suggestion was also offered by Larson (1990) to explain the lack of prior discovery of an ancient forest of stunted Thuja occidentalis on the apparently bare cliffs of the bare-looking Niagara Escarpment in southern Ontario, Canada. The small size of many cliffs often results in them being viewed as ‘break-points’ or transition-points in landscapes, rather than as separate landscape elements. This view leads to the characterization of cliffs as the ‘edges’ of other places, rather than places in their own right.

We feel that all of these factors help to explain the small amount of scientific literature dealing with the vegetation of cliffs compared to the vast amount of literature on level-ground forests, grasslands, wetlands, deserts, and tundras of the world.