SYNTHETIC CHARACTERS OF THE COMMUNITY 



73 



Epiphytic Communities. — The structure of epiphytic communities 

 has been critically studied by Ochsner (1928). On one tree are often 

 found several associations under different external conditions, so that 

 the following relations should always receive attention : 



1. Species of the host plant, exposure (in the open or not), human intervention. 



2. Height of tree, width of crown, height to first branch, diameter of trunk or 

 circumference 1 m. above soil, form of stump (base). 



3. Course of water from the crown (centrifugal or centripetal); in mountains, 

 average depth of snow. 



4. Character of bark: thickness, physical peculiarities (smooth, rough, fur- 

 rowed, etc.), water capacity. 



5. Collection of humus on the host plant. 



6. Height and exposure of the epiphj^tic society. 



According to Ochsner, trees show four well-defined parts, which 

 correspond to four different habitats (Fig. 40) : 



Crown 



Fig. 40. — Habitats of epiphytic communities on trees. 



(After Ochsner.) 



a. Crown, in the crotches of which humus often collects. 



b. Crown base, protected from direct sunlight in exposed trees and therefore 

 also more moist than the middle of the trunk. 



c. Trunk, the middle part, which in open stands is exposed to wind and sun 

 (Fig. 41). 



d. Stump, where the vegetation catches the water that runs down, and retains 

 it longest. 



In the investigation of the structure of the association it is sufficient 

 to record the cover and perhaps the vitality of the species. 



Association Tables. — The absolutely necessary foundation of every 

 critical study of communities is the "association table." At the head 

 of the table is placed the most precise possible statement of the 

 ecological characteristics of each sample (stand). Such a statement 

 reduces the requirements for ecological description in the text and 

 establishes the ecological resemblances of the communities. These, 



