286 CAIN, DE OLIVEIRA CASTRO, PIRES, AND DA SILVA 



At Mucambo the tree flora is so rich in species and the density of most 

 of them is so low that it is obvious that sample plots of small area would 

 not discriminate among the frequencies of the various species. In other words, 

 nearly all species would have low percentages. For this reason we have cal- 

 culated frequency of the species on a basis of the 20 sub-plots that are 10 X 

 100 m. and the 10 sub-plots of 20 X 100 m. Since the number of frequency 



Table 7. The occurrence of tree species in Ramikiaerian frequency classes in equa- 

 torial rai?i forest at Mucambo 



classes is as great as the number of sub-samples, it is customary to use a 

 limited number of classes. We follow the system of Raunkiaer (1934) and 

 use five even-sized classes as shown in table 7. On a basis of the 10 X 100 

 m. sub-samples, only four species attained class E (81 to 100 per cent) fre- 

 quency: Eschweilera odor a, Protiunn trifoliolatum, Eschweilera krukovii, 

 and Protium sp. ? ("Breu mescla"). With the sample size doubled in area, 

 four additional species attained this class: Tovomita stigmatosa, Vochysia 

 guianensis, Iryanthera juruensis, and Theobroma subincana. Also with rela- 

 tively high frequency, class D (61 to 80 per cent), were five additional species 

 for the smaller plots and 10 for the larger ones. At the other end of the 

 scale is found the vast majority of the species which have low frequencies 

 (75.8 and 70.5 per cent of the total species in the two sizes of sample areas) 

 and are encountered only occasionally in the forest. 



Relative measures. Tables 8, 9, and 10 have been prepared to give some 

 of the specific data that have already been mentioned and also to show the 

 relative positions of the leading species according to each of the measures. 

 Relative density (table 8) is the per cent which the density of a species (on 

 the total sample) is of the total density of all species. In the same way 

 relative basal area (dominance) (table 9) is the per cent that the basal area 

 of a given species is of the total basal area on the plot, and relative frequency 

 is the per cent the frequency of a given species is of the sum of the frequencies 



