VEGETATIONAL ANALYSIS 



71 



ture, homogeneous, undisturbed stands of virgin forest would re- 

 quire the observation of only small portions of individual stands 

 and a relatively small number of stands to give dependable infor- 

 mation. In younger, less stable vegetation, more stands and a wider 

 observation would be necessary so that variation would be repre- 



€0 



Frequency 



Constance 



12345 ABCDE 12345 



FlG. 30. Presence, frequency, and Constance diagrams for Sierran red fir 

 forest, based on sixteen stands. The presence diagram is normal, especially in 

 the absence of a second maximum. The Constance diagram is constructed 

 from regular quadrat data rather than a Constance sample. Compared to a 

 frequency diagram it should show a material decrease in Class 1 because of 

 the greater odds on discovery of a single plant of an accidental species in a 

 restricted area. Surprisingly, with only forty species, it retains the same form 

 as the presence diagram (ninety-seven species) although the high Constance 

 classes are reduced. The frequency graph is normal, and indicates stands of 

 relatively great homogeneity. 



sented and so that those species seldom present or rare would fall 

 into their proper classes. What this minimal area should be and 

 what the minimum number of species might be for the community 

 must largely be determined by experience and familiarity with the 

 community. 



Constance.— When a unit area in each stand instead of the en- 

 tire stand is used for listing species, as for presence, the values are 

 termed Constance. There is thus no fundamental difference be- 



TABLE 4. Portion of a presence table compiled from sixteen stands of vir- 

 gin red fir (Abies magnified) forest in the Sierra Nevada. Only Abies mag- 

 nified and Pinus monticola, of the trees, are constantly present (Class 5). 

 Only one shrub, Kibes viscosissimum, is a constant, others falling in Class 3 

 or lower. Five herbs are constants, eight are mostlv present (Class 4), and 

 five are often present (Class 3). Eleven herbs of Class 2 (seldom present) and 

 46 of Class 1 (rare) are not listed. 189 



