IMPORTANT RANGE PLANTS. 55 



SUMMARY. 



ECOLOGICAL REQUIREMENTS. 



The figures given in Table 2 represent the relative water require- 

 ments of the different important forage plants studied. 1 Owing to 

 the importance of having the plants advanced to as nearly the same 

 point of development as possible when the drought tests were made 

 aerial conditions were slightly different. The error due to this fact, 

 however, is very largely offset by the dupli cation of the tests in the 

 case of virtually all species. 



It is a well-established fact that the amount of moisture remaining 

 in the soil when the plant wilts beyond recovery is determined by 

 the physical structure of the substratum. The object in making the 

 wilting coefficient determinations, then, is principally to show (1) 

 that certain species occupy quite different soil types, and (2) that 

 the soil types (textures) are widely contrasted as shown by the 

 notable difference in the wilting coefficients for the various species. 

 For example, mountain bunch grass (Festuca viridula) does not wilt 

 seriously in the soil in which it characteristically grows until the 

 water content is reduced to between 7 and 9.5 per cent. This plant 

 is adapted to coarser and less rich soils than is mountain onion 

 (Allium validum), for example, which is confined to exceptionally 

 black, mealy soils, and which wilts beyond recovery when the soil 

 moisture content drops to between 14 and 16 per cent. Owing to 

 the relatively small amount of moist soil found in mountain range 

 lands, it is evident that a species like mountain onion would not 

 occur nearly as abundantly as mountain bunch grass. 



As a means of comparing habitat requirements, the species are 

 grouped in three classes as follows : 



Class A, plants of high moisture requirement — those inhabiting 

 saturated soils, such as open marshes, wet meadows and bogs; class 

 B, plants of medium moisture requirement — those inhabiting rela- 

 tively heavy soils which are saturated during the early part of the 

 season, but later contain a medium amount of moisture; and class C, 

 plants of low moisture requirement — those occurring in well-drained 

 lands, open glades, and exposed situations. 



It will be observed that practically three-fourths of the most 

 valuable forage species are dry-land plants. This fact is of high 

 economic importance, since the major portion of the range lands are 

 well drained and afford conditions favorable only to plants which 

 are comparatively drought resistant. 



It is noted that a few species fall under more than one head so far 

 as concerns their habitat requirements — that is, they are not strictly 



1 A resume of the potent climatic factors under which these tests were conducted was published in the 

 Journal of Agricultural Research, Vol. Ill, No. 2, 1914, "Natural Revegetation of Range Lands Based upon 

 Growth Requirements and Life History of the Vegetation," pp. 95-102. 



