PirS'THETrC CHAnACTERS! W TnE COMMUNITY 



57 



Constancy Diagrams. — The constancy curve and constancy diagram 

 are for the association what the frequency curve and frequency diagram 

 are for the stand (Assoziationsindividuum) . The course of the curve is 

 very different from that of frequency, in that the two lowest-class 

 numbers show a distinct maximum. The highest-constancy classes 



I E M w V 



10-20 zo-w Ho^oemso- 100% 



I n m 17 V \ Classes of 

 10-20 20-w VMO 60-80 80-100% j consfani^ 



Fig. 36. — Constancy diagrams of the Elynetum. A, Ten samples of 4 sq. m. 

 from 10 stands from central and eastern Orisons; B, the same with the addition of two 

 4-sq. m. areas from the southern Tirol. 



have few species but would have more if the size of the test plots were 

 enlarged. A sharply defined association, not very homogeneous but 

 rich in species, like the Elynetum of Braun-BIanquet, gave the accom- 

 panying diagrams (Fig. 36). The areas used for these determinations 

 of constancy were smaller than the minimal area of the association. 



Fig. 37. — Constancy and presence diagrams of the Polytrichetum sexangularis of 

 the Central Alps. A, Constancy from 10 tests in as many stands; B, Presence diagram 

 of 15 well-developed stands of 2 to 10 sq. m. 



But larger and more homogeneous areas of the Elynetum are not easily 

 found. 



With these may be compared the Polytrichetum sexangularis of the 

 Alps, an association of very few species and of very great uniformity, 

 whose minimal area does not exceed 1 sq. m. (Fig. 37). Of these 

 diagrams B is based upon 15 naturally bounded, normally developed 

 stands of 2 to 10 sq. m. Compared with the constancy diagram A 



