56 



PLANT SOCIOLOGY 



But sometimes the normal characteristic combination of species 

 can be verified on smaller areas (see Table 4, Nos. 4, 9), and contrari- 

 wise it may under some circumstances remain incomplete on a plot 

 considerably larger than the minimal area. Consequently in every 

 record of an association taken for the purpose of tabulation it is neces- 

 sary to be careful that the normal characteristic combination of species 



(^ 



Fig. 34. — Sample plots of the same size taken from eight individual stands of the same 

 association for the determination of constancy. 



is present and that the requirements of the minimal area are approxi- 

 mately fulfilled. 



For the determination of constancy each stand may be examined only 

 once by means of a sample bit of vegetation of a definite size (Fig. 34). 



a b 



c 



Fig. 



35. — Plan for the determination of constancy and presence from the same stand 

 beginning with the quadrat (o) which is 1 sq. m. 



If the size of the sample areas chosen for determination of con- 

 stancy is 10 sq. m., then the floristic composition of one 10-sq. m. plot 

 in each stand will be examined minutely. The species lists are then 

 tabulated together, and the species are distributed into 5 or 10 con- 

 stancy classes according to their occurrence in the lists, as in the 

 determination of frequency or presence. As with frequency, the 

 constancy numbers depend on the size of the plots studied, the number 

 of constant species increasing with the size of the plots. 



Constancy determinations are readily united with presence deter- 

 minations. In each normally developed stand a small definitely 

 bounded trial plot is laid out (a), then a second and third larger (6, 

 c), and then notes are taken on the species present in the stand (d) 

 outside the trial plots (Fig. 35). A similar procedure may be followed 

 in determining the species-number: area curve. 



