Studies on the Succession and Ecology of Epiphytic 

 Bryophyta on the Bark of common Trees in Denmark. 



A summary of the preceding paper. 



By 



Carsten Olsen. 



In woods, the epiphytic Bryophyta are always found on the one side 

 of a tree-stem and not on the other; this latter, however, frequently ex- 

 hibiting a growth of lichens. Most forest trees deviate more or less from 

 the perpendicular, and it is on the upper side of such inclined trunks 

 that the Bryophyta are found (Fig. 1). This is due to the fact that 

 rain in a wood always falls very nearly vertically, with the result that 

 the upper side of the tree-trunk, being more directly exposed, obtains 

 a greater share of the rainfall than the lower. The bryophytic vegeta- 

 tion is most abundant upon trunks with an inclination of over 10°, 

 whereas upon perpendicular stems, such growth is either very scanty 

 (Table 2) or altogether lacking. In the case of trees standing in the 

 open, however, the rule as to restriction of bryophytic growths to the 

 upper side of the trunk does not apply; the Bryophyta are here as a 

 rule very scarce, especially upon windy sites, being found singly, and 

 on all parts of the stem. This is due to the fact that on open ground, 

 the rainfall is rarely vertical, but may come from all quarters. On 

 such isolated or exposed trees, the lichens are of far more frequent 

 occurrence than the Bryophyta. 



The composition of the bryophytic vegetation is determined by 

 the following factors: 



1. Age of the tree. 



2. Position as regards light. 



3. — — — wind. 



4. — — — rainfall (i. e. angle of trunk). 



5. Species of tree. 



6. Chemical composition of the soil (local abundance or paucity 

 of chalk). 



Of these, No. 1 is the most important. We thus find a succession 

 of bryophytic communities. Certain features are here common to all 



