424 THE INVESTIGATION OF SUCCESSION. 



development of what appear to be different stages of the same sere. In this 

 way the whole course of succession may actually be traced in a few years by 

 the same individual. The one difficulty hes in properly articulating the differ- 

 ent portions thus studied, and here he must call inference to his aid, or, what 

 is better, make a special synchronous investigation of the actual development 

 between every pair of stages. As a matter of fact, intensive investigation 

 of this sort makes it evident that he must avail himself of both sequence and 

 experiment wherever possible. The complete method, then, begins with 

 inference, but rests primarily upon sequence, reinforced to the highest degree 

 by experiment. 



The method of experiment is a highly desirable, if not an indispensable 

 adjunct to the method of sequence. Its great value Hes in the fact that it 

 makes it possible to reproduce practically any or all portions of the course of 

 development, and to keep them under intensive observation. Its use is 

 imperative in climax areas which show few or widely scattered serai communi- 

 ties, while it greatly reduces the period necessary to secure conclusive results 

 in an area where developmental stages predominate, as in some mountain 

 regions. It is especially dependent upon the quadrat method, and will be 

 further discussed in that connection. 



Special methods. — ^The special methods of successional investigation may be 

 grouped under four heads, viz, .(1) quadrat method, (2) mapping, (3) instru- 

 mentation, (4) recording. All of these are intensive in nature and in purpose, 

 with the exception of large-scale mapping, and hence find their use in connec- 

 tion with the general methods of sequence and experiment. The quadrat 

 method is the essential basis of them all, and may alone suffice for the study of 

 development pure and simple. The latter can not be understood, however, 

 without a thorough analysis of the habitat and the plant reactions upon it, 

 and for such work instruments are indispensable. Moreover, much ecological 

 work has failed of its pmpose for the lack of an adequate method of record. 

 Such a record becomes all the more imperative with the increase of intensive 

 investigation, and it must soon come to be recognized that no successional study 

 is complete without a detailed record of observation and experiment. This 

 record shoiild be wholly separate from its interpretation, a result which can 

 be secured only by the impersonal methods of quadrating and instrumentation. 

 Mapping is primarily a method of record, but it is also possible to use it in con- 

 nection with quadrat and instrument for purposes of investigation. 



THE QUADRAT METHOD. 



Concept and significance. — ^The quadrat method is regarded as comprising 

 all the exact methods of determining the composition and structure of plant 

 commimities, irrespective of the shape or size of the measure. While no defi- 

 nite line can be drawn between methods of quadrating and mapping, the latter 

 is here considered to be upon a scale which does not permit dealing with indi- 

 viduals, and hence mapping must confine itself to the distribution and relations 

 of communities. It is clear that the two may be used conjointly in the same 

 area and combined in the final record, as is shown later in the methods em- 

 ployed by the Botanical Survey of Minnesota. While this basic method of 

 successional study is named from the most important measure, the quadrat, 

 it includes also the transect, bisect, and migration circle. While all of these 



