436 THE INVESTIGATION OF SUCCESSION. 



they deal chiefly with the outline of units, but they are on such a scale as to 

 show much of the detail as to composition. 



Ecotone maps (Clements, 1905 : 181) have to do with the relations of zones 

 and altemes. Because of the essential relation of the latter to succession, such 

 maps furnish a graphic summary of the course of development, either actual or 

 potential. In the one case, the map shows the zones or stages of an actual 

 sere on a small scale, as in the case of ponds and streams. In the other, the 

 zoned climax associations of an entire region are shown on a large scale in the 

 potential sequence of the cUsere. In either case, the map is constructed by 

 locating and tracing the ecotones between the various zones, usually with the 

 topographic featiu-es indicated in so far as they have a bearing upon develop- 

 ment. 



Survey maps. — In the methods of vegetation survey developed by the Botan- 

 ical Survey of Minnesota, an endeavor has been made to combine the advan- 

 tages of topographic and ecotone maps with those of quadrats. From the 

 nature of American subdivisions, the unit is the township, consisting of 36 

 square miles or sections. Each section is divided into four quarter sections a 

 haJf mile square, and each of these into "forties" a fourth of a mile square. 

 The mapping unit is the "forty." This is mapped on a square decimeter of 

 cross-section paper, the four maps for each quarter section being placed in 

 v^ their proper relation upon one sheet. The scale is approximately 1 to 4,000. 

 Topographic and artificial features and the ecotones of communities are mapped 

 in detail. Cultural as well as natural communities are indicated, while at 

 »- least one quadrat or transect is charted for each "forty," the number depend- 

 ing upon the differentiation of the vegetation in it. Instrument readings are 

 taken in the quadrats or at the ecotones, and photographs are made to accom- 

 pany the charts throughout. As a consequence, a complete record is obtained 

 of topography and the structure and development of vegetation, with some 

 idea of the physical factors involved as well. When supplemented by inten- 

 sive studies of prisere and subsere in the different climaxes, a complete pic- 

 ture of the vegetation is obtained. The application of the results of such a 

 survey also becomes a matter of prime importance to forestry and grazing 

 and to the agriculture of new or neglected regions. 



Climax maps. — ^The general treatment of vegetation as static has resulted 

 in the production of many maps in which no distinction is drawn between 

 climax and developmental communities. From the nature and extent of 

 climax formations, vegetation maps of regions and continents have been con- 

 cerned with them primarily, but with Httle or no recognition of basic develop- 

 mental relations, such as that of the clisere. Vegetation maps have been 

 constructed from many sources of diverse value, and can only be regarded 

 as provisional to a large degree. The existence of a great climax vegetation is 

 so patent that its general area can readily be indicated, but its definite relation 

 to other climaxes, its exact boundaries, and especially .the problems of such 

 transition areas as prairie, chaparral, and mixed forest can only be settled by 

 intensive studies. Hence the construction of reUable climax maps must follow 

 the investigation of developmental relations and the accurate tracing of great 

 ecotones rather than precede them, as has usually been the case. However, 

 it is clear that it is necessary to construct such maps from time to time as our 

 knowledge grows, in order that they may serve as working bases for further 



