IMETHODS OF STUDYING VEGETATION 205 



mark out each decimeter strip, and the plants are checked off 

 as they are found. Except in cases of unusual difficulty, plants 

 should never be broken or pulled as they are counted. Clusters 

 and bunches of stems from the same root are counted as single 

 plants, and the number of stems indicated by an exponent. In 

 the case of bunch-grasses, each bunch is counted as one plant. 



220. Abundance. Species are arranged in the quadrat list 

 upon the basis of their abundance, i.e., number of individuals. 

 They are also divided into groups which correspond to the various 

 degrees of abundance. Two types of abundance are recognized, 

 owing to the fact that the individuals of some species occur in 

 groups, while those of others are more or less uniformly arranged. 

 The former are said to be gregarious, the latter copious. The 

 species counted are classified with respect to the following table 

 of abundance: 



Social exclusive, no other species of vascular plants present. 

 Social inclusive, more than 100 in the quadrat. 



While the number of plants per quadrat gives a much clearer 

 idea of the relative importance of the species than the usual terms 

 abundant, common, rare, etc., height and width have much to do 

 with the question of importance. The part which a species plays 

 in giving character to vegetation and its relation to the habitat 

 can be determined only by taking into account the space it 

 occupies, as well as its abundance. This may be done with sufficient 

 accuracy, after finding the average height and width of the plant 

 body of any species, by means of the formula, height (Tri?^) x abun- 

 dance. 



221. The chart quadrat. Whenever it is desired to obtain an 

 exact record of changes of structure, the chart quadrat is used. 

 The meter quadrat is preferable on account of the labor involved 

 in charting. The location must be decided by the area to be 

 studied and by the facts to be brought out. Chart quadrats are 

 used chiefly for comparing representative areas of different forma- 

 tions or diverse areas of the same one, as well as the spring, 

 summer, and autumn aspects of the latter. 



