Apr.' 'is, 1920 Native Vegetation of Northern Great Plains 



69 



with the exception of a few annual species, the basal cover to be prac- 

 tically the same in both years. If the maps had been drawn on the basis 

 of the foliage cover, there would have been a great difference between the 

 1 91 5 and 1 91 6 maps. The photographs illustrate this difference more 

 clearly than would be possible by quadrat maps. But if the maps are 

 drawn on a basis of the basal cover, various maps of a given quadrat 

 would show actual changes as they occur from grazing. This is really 



Fig. 2. — Meter quadrat in 30-acre pasture mapped in detail in 1915. Cross hatching represents BouUloua 

 gracilis; vertical hatching, Stipa comata. The presence of other species is indicated by dots and out- 

 lined areas. 



the important point in relation to grazing systems. If grazing has been 

 severe, the basal cover is likely to be changed rapidly, but under normal 

 conditions it should change gradually. This is especially true in such 

 regions as Mandan, where most of the vegetation is made up of perennial 

 species. Sampson (5) says in regard to increase of ground cover: 



The increase in actual stand or ground covered was due almost entirely to the 

 enlargement of the tufts, and text figiu-es 5 and 6 show that even under season-long 

 protection the bunch-grasses and other valuable plants do not increase rapidly by 

 this means. 



