ing are determined, charting or measurement of the vegetation 

 is often made at a height of 1 in. — the height to which many 

 species are grazed — and the data presented as basal area. The 

 spread of herbage is influenced not only by the grazing of live- 

 stock, but also by attacks of insects, by fungi, and by weather con- 

 ditions. Therefore, since basal area is more stable under such 

 seasonal influences, although subject to long-continuing in- 

 fluences, its use as a means of measurement is preferred for many 

 purposes. 



Herbage area is one of the most important characteristics of 

 vegetation in determining the nature of a community, such as 

 quantitative relations between species. For example, the sand 

 dune-sage type in the southern Great Plains was found to con- 

 tain a total of 50 species of grasses and 216 species of forbs and 

 shrubs. The average cover of all the vegetation was 34.3 per 

 cent, which was divided among the following: Artemisia Jilifolia, 

 79.2; Bouteloua gracilis, 6.3; Sporobolus cryptandrus, 5.3; other per- 

 ennial grasses, 2.4; annual grasses, 0.9; other shrubs, 4.9; and all 

 forbs, 1.0 per cent.'^^ A species may vary greatly in cover in 

 various stands, as shown by Vaccinium uliginosum in Alaska, which 

 varies in average herbage cover from about 22 per cent in stands 

 where it is one of the dominants to 9 per cent or less where it is 

 not a dominant. ^'^^ Cover is often the most suitable expression 

 for recording change (see Chart 4), but for single- or few-stalked 

 plants, population density is a better characteristic to use. 



Many methods have been used in securing data on cover, in- 

 cluding ( 1 ) charting by hand or with a pantograph which is set 

 up on a low table, (2) area listing, (3) point-contacts, and (4) line- 

 interception; and various estimation methods such as (5) cover 

 scales, (6) point-observation plot or square-foot density, and (7) 

 ocular or range reconnaissance. The methods have been described 

 in numerous publications and summarized and evaluated in a 



In Europe, sample areas to establish the relative importance 

 of species in vegetation have been in use for more than a century. 

 Sample areas for determining changes caused by grazing or in- 

 duced by various kinds of management procedures, or to chart 

 the course of succession following disturbance, may be established 



Aamalytic CHaracteristics of tHe ComMtimmnity • 103 



