permanently; or they may be set up temporarily for the purpose of 

 ascertaining the present plant composition or other charac- 

 teristics. 



A stand may be sampled by a single, carefully located area, pref- 

 erably starting at 10 m^ and then enlarging it to 50 or 100 m^ 

 for a second look, as is commonly done in central Europe;^^ or 

 it may be sampled by a number of small areas distributed 

 throughout the stand, as is the usual practice in North America 

 and Scandinavia. The size of the sample area to use depends 

 upon the kind of vegetation that is being studied; in grasslands 

 it is usually a square meter, in forests an area 10 meters square. 

 For reliable results, a large number of sample areas should be used 

 — the smaller the sample area the larger should be the number. 

 In a grassland stand that is fairly homogeneous and not too large, 

 20 sample areas are usually adequate, while in a forest stand at 

 least 10 should be used. The advantage of employing many small 

 sample areas is that each stand can be studied very thoroughly, 

 while the advantage in using one or a few large samples is the 

 saving in time so that more stands can be investigated. 



Height of Plants 



The height of plants is usually a very good indicator of their 

 condition or vigor, and, therefore, can be employed as a criterion 

 of the success of a species in various habitats. It can also be used 

 as a measure of the favorableness of the environment (Figure 

 1-11) and is much used by foresters as an index of site quality for 

 various species of trees. Usually there is a good correlation, as high 

 as 0.9 or even more, between the rate of growth in height and 

 growth in weight; hence, growth curves are often based on height 

 measurements instead of dry weights because of their convenience 

 (see Chart 5). 



It is somewhat difficult at times to secure accurate measure- 

 ments because the height attained by the stems and leaves varies 

 with individual plants of the same species growing under similar 

 conditions. The approximate average height of the herbage in 

 fairly dense stands can be secured by sighting along the top of the 

 vegetation with a ruler, or the maximum and minimum heights of 



Aztalytic Characteristics of the Comxtmiazmity • 105 



