578 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



in that light, and they may be only local as emphasized in the next 

 paragraph. 



If, as we often do when walking over a meadow, we come upon a 

 clump of coarse Rushes, this is a strong indication of damp con- 

 ditions ; if the Rushes are in a temperate region and accompanied 

 by such hygrophytes as Marsh-marigold {Caltha pahistris agg.), this 

 combination can be taken as a sure sign of lasting percolation or of 

 a water-table near the surface. Conversely, certain Heaths and 

 Lichens are indicative of dry conditions, and certain forbs of a 

 calcareous substratum — at least in many parts of the world. Whereas 

 a single indicator species may be usefully suggestive, it is far better 

 to have a group of them, which with suitable experience may be 

 taken as virtually infallible. But even as the flora and vegetation 

 change in different areas, so may such indications, which individually 

 are chiefly of local use ; consequently precise local knowledge is 

 needed for their application. 



Accordingly it would seem superfluous in this very general treatise 

 to multiply the examples. Suffice it to repeat that land-use science, 

 employing such methods as plant indicators, can be of very great 

 importance to the modern world. 



Of other plant geographical or, often, primarily ecological principles 

 and findings that have wide applicational value there are very many 

 — as indicated, for example, in the concluding sections of Professor 

 H. J. Costing's work cited at the end of this chapter, though the 

 examples he gives are mainly North American. These principles 

 include many that are widely employed : in horticulture, for 

 cultivated plants are as subject as any others to ecological laws ; in 

 agriculture, where so many of the practices, however familiar and 

 widespread, are basicallv ecological ; in pisciculture, where the 

 feeding and maintenance of a rich phytoplankton is all-important ; 

 in silviculture, e.g. towards deciding whether to maintain temporary 

 forests of a successional nature or to let the stands develop naturally 

 towards the chmax ; in reforestation of suitable areas (after deciding 

 which areas are suitable) and revegetation of exposed soils, where 

 special autecological and local synecological knowledge are normally 

 essential for success ; in range management, which is largely applied 

 ecology, though it should be recalled that the most effective practices 

 are in general those which least disturb the natural balance between 

 the grassland and its environment ; in pasture and various cropland 

 choice and treatment, e.g. in relation to suitable indicators and 

 rotations ; in general land-management, which raises the questions 



