Some Observations on the Epiphytic Moss Flora of Trees in Argyll

Abstract

This district offers a favorable habitat for mosses owing to the cool winds and heavy rainfall. The mosses upon various spp. of trees were studied, special attention being paid to oaks, since they appear to form natural woodland and also because the moss upon them is evidently affected by exposure. On sheltered trees the moss and lichen covering was heavy on trunk, branches, and even small twigs, and showed marked zonation. As exposure to the prevailing winds increased the moss covering became scantier, its zoning much less marked, and the vertical extent of the zones much reduced. The lowest zone on sheltered trees consisted of moss-carpet species, the middle zones of Eurhynchium myosuroides, Hypnum cupressijorme and H. cupressijorme var. filiforme, and the top zone of pioneer species such as Ulota crispa and Pylaisia polyantha. A comparison of trees on which the mosses were zoned with those on which they were not showed that the mosses most commonly found on the latter were pioneer spp., e.g., Ulota and Pylaisia. A correlation of zonation with exposure showed that all sheltered trees, and less than half the exposed trees were zoned. The results obtained for ash and other trees of which fewer individuals were examined confirmed those obtained for oak. The moss covering of ash trees was not on the whole so dense as that on oaks. Pioneer spp. appeared in lower zones than on oaks. Some study was made of the autecology of some of the most frequently encountered spp. A comparison was made of the commonest mosses growing on oak, ash. birch, and sycamore, and it was shown that the pairs oak and birch, ash and sycamore, behaved differently. The differences were accounted for chiefly by differences in the roughness of the bark, chem. differences playing only a small part.