l8] PLANT ADJUSTMENTS AND APPLICATIONS 567 



as Man's manipulation of vegetation have been at least touched 

 upon elsewhere in this work ; many are dealt with in more worthy 

 detail in recent books on conservation and allied topics. Agricul- 

 ture, horticulture, and forestry themselves are to a large extent 

 dependent upon Man's manipulation of habitats and cognate plant 

 communities, whether the latter consist of individual crops or 

 mixed ones. 



The practical value of the concept of plant communities is widely 

 recognized to be considerable in forest, range, and wildlife manage- 

 ment — e.g. in North America — and in vegetation mapping for land 

 use as often practised elsewhere. Thus in the United States, land 

 utilization and management are happily to a considerable and ever- 

 increasing extent based on the indications afforded by vegetation 

 and on the potentialities of its growth — for example, after the manner 

 outlined in the last chapter. Moreover, many of the most scientific- 

 ally based and successful practices involve the judicious modification 

 of existing vegetation rather than the creation of new, ' artificial ' 

 forms. For such practices the careful recording of the species con- 

 cerned, as well as of the density and composition of plant commun- 

 ities, is often important. Usually, samples are taken as a basis for 

 estimating the general conditions or productivity of the plant cover 

 over the area of which the samples are representative ; comparable 

 sampling elsewhere may also serve as a standard for comparing the 

 vegetation of different areas. 



The methods employed in sampling vegetation include the use of 

 quadrats, which are test areas (commonly squares, hence the name) 

 of designated size in which the kinds and numbers (or areas) of 

 plants are recorded, and of transects, which are cross-sections of 

 vegetation studied along a line or belt. A line transect is one in 

 which there are recorded, by names or symbols, the plants touching 

 or overlapping a string stretched along the ground, while a belt 

 transect represents a band of vegetation of designated width. In 

 each case the recording should be done on a diagram drawn to scale. 

 A belt transect is essentially an elongated quadrat and is usually 

 far more instructive than a line transect, but it is more tedious to 

 construct and record. Also involving intensive labours is the bisect, 

 which is a cross-section of vegetation as it is revealed by a trench 

 extending down to the deepest roots. For the investigation of suc- 

 cession, permanent quadrats may be established and studied from 

 time to time. Clip quadrats, in which can be determined the oven- 

 dry weight of the total vegetation clipped from the test area, are 



