Clare Island Survey — Tree- Grow ih. 9 29 



winters would also enable a great increase to take place in the spread of 

 Gorse, beneath which seedlings of Pine would be quickly smothered. "While 

 this theory does not satisfactorily explain the total disappearance of the tree, 

 it affords a possible reason for its speedy destruction when semi-civilized 

 man came on the scene, and commenced to burn the Gorse and Heather for 

 the sake of providing rough pasturage — a process which would destroy 

 seedlings and young trees on many areas of mountain which probably 

 formed the last stronghold of the Pine. One possible natural factor in the 

 process of extinction maj r be mentioned. Many stumps of Fir in bogs show 

 the " rliizomorphs " or mycelium of Agaricus mdleus, the Honey Fungus. This 

 fungus is particularly fatal to young Pines, and when the latter are planted 

 on woodland cleared of Oak, Ash, or other broad-leaved species, large numbers 

 succumb. On a soil more or less permeated by the mycelium of this fungus, 

 as is old Oak and Ash woodland, the Pine may have had an enemy of con- 

 siderable virulence to contend with, and this, added to the shade and thick, 

 loose, humus layer, may have practically exterminated it from large areas. 



At what period the Pine ceased to be a recognizable component of the 

 forest flora of Clare Island is difficult to say. If the absence of Pine from 

 the higher-lying forest zone is confirmed, it appears probable that the species 

 disappeared from the island earlier than was the case on the mainland, as 

 there is no trace of it under the mountain peat which covers the Oak stumps 

 on the former, while it occurs everywhere under mountain peat on the main- 

 land. Submerged forests on Achill Sound, Tullaghan and Bellacragher Bays, 

 &c, show that Oak and Pine formed a mixed forest when the sea-level was 

 from five to ten feet lower than at present, while the same mixture in the 

 lowland peat-bogs occurred previous to the formation of Sphagnum peat. As 

 already pointed out, an increase in the temperature would favour rather than 

 prevent the spi-eading of Pine onto the higher ground, but the preservation of 

 the stumps would only occur when they were covered with peat. If the 

 formation of the mountain peat on Clare Island took place at a later period 

 than that on the mainland, owing to more favourable soil conditions or other 

 causes, the Oak may have succeeded in suppressing the Pine on the restricted 

 area available for tree-growth on the island before mountain peat-formation 

 began, while on the poorer soils of the Achill and Belmullet areas, the 

 extension of Oak would be hindered on the one hand, and the peat-formation 

 hastened on the other. There are several reasons for supposing that mountain 

 peat was not extensively developed at high elevations, or in the west of 

 Ireland, until after the climatic optimum, a period corresponding to the 

 greatest development of the Oak and Hazel flora. Wright 1 supposes that 

 this optimum occurred in early Neolithic times, about the time the sea had 



1 " The Quaternary Ice Aye." 



