Experimental Vegetation
356. Scope and methods. The experimental study of the formation as a complex organism rests upon methods essentially similar to those discussed under experimental evolution. The scope of the two fields is practically the same, moreover, in that both deal with the experimental development of an organism and the structures that result. The actual problems are naturally very different, since the formation is a complex of individual plants, but the fundamental basis of habitat, function, and structure is common to both. However, the functions now to be considered are aggregation, invasion, competition, etc., and the structures, zones, consocies, societies, communities, and families. The latter may properly be regarded as adaptations called forth by the adjustment, i. e., aggregation, migration, ecesis, etc., of the formation to the physical factors of the habitat. As consequences of measured factors, formational adjustment and adaptation must themselves be carefully measured and recorded. For these purposes, the methods of quadrat and transect, of chart, photograph, and formation herbarium are used. Invaluable as they are for any scientific inquiry into vegetation, such methods form the very foundation of experimental study in which accuracy is the first desideratum.
It has already been shown that nature’s own experiments in the production of new forms furnish the best material for experimental evolution. This statement is equally true of experimental vegetation. The formation of new habitats by weathering and transport, and the denuding of old ones, yield experimental plots of the greatest value. This is likewise the case in the great majority of formations, where invasion or competition is active. These are the phenomena that must be considered in any careful study of vegetation, but in taking them up from the experimental standpoint, greater attention must be paid to detail, and the changes must be followed closely for a longer time. The method that makes use of existing changes in vegetation is designated the method of natural habitats. In contrast with this is the method of artificial habitats, in which the habitat itself is definitely modified, or a group of species actually transferred to a different habitat. Many problems of vegetation can be attacked with greater success under control than in the field. This is particularly true of competition, in which results can be obtained most readily by means of the method of control habitats, as carried on in the plant house.