as creosote bush (Larrea dwancata) in Arizona deserts. However, 

 the use of additional species, at least the chief dominants of the 

 various layers, is preferable. 



Often in descriptions of vegetation only the more abundant, 

 dominant, or "most important" species are listed, and only the 

 number instead of the names of "unimportant" species is given, 

 even though the plants in the latter group may make up a con- 

 siderable proportion of the vegetation. It is essential scientifically 

 and more useful practically, to include all species, because some 

 which appear insignificant at the time of the investigation may 

 indicate conditions that existed at an earlier time but are not pres- 

 ent now; or they may indicate, as "prediction species," a future 

 trend. Complete lists furnish material for, and are frequently 

 used by, later investigators in ways not considered by the original 

 worker. All species play some part in a stand, and no investigator 

 has the right to presume unimportance in Nature; for example, 

 the cutleaf violet ( Viola pedatifida) is considered one of the best in- 

 dicators of tallgrass prairie conditions in Iowa, although it is 

 inconspicuous and has little or no forage value compared to the 

 tall bunch grasses.' 



Other small plants often appearing insignificant, such as mosses 

 and lichens in the Arctic and Subarctic (see Figure 2-1), have 

 narrow but different ranges of amplitude, so they are particularly 

 valuable as indicators of soil and microclimatic conditions, of 

 overgrazing by reindeer or caribou, or of successional status. 

 Herbaceous forest plants, although often inconspicuous, are more 

 delicate indicators of soil conditions than trees, and have been 

 used in the delimitation of communities.^^ In rich mesophytic 

 forests in the eastern United States, mull humus supports a lux- 

 uriant herbaceous flora including Viola canadensis, V. palmata, 

 Phacelia bipinnatifida, Disporum lanuginosum, and several ferns; 

 while mor humus, especially characteristic of coniferous forests, 

 has a different, sparse flora including Lycopodium spp., Cornus cana- 

 densis, Maianthemum canadense, and Trillium undulatum.'^^ Another 

 example of the importance of the so-called "insignificant" species 

 is seen in southern Arizona, where minor grasses of the mesa- 

 range type, although each one makes up less than 1 per cent of 



80 • Tke CoMimmiEzmity 



