228 MINNESOTA BOTANICAL STUDIES 



vanica. These Carcx societies which appear to l)e closely depend- 

 ent upon a relatively lii^h soil-moisture relation of the vernal 

 period, persist for about two weeks after which all trace of their 

 presence is soon obliterated with the coming of drier days. 



Another grass which sometimes assumes a distinct bunch-grass 

 form in exposed situations is Panicum virgatum. However, this 

 species reaches its maximum in the numerous pockets which partly 

 characterize the "choppy hills." Here this grass often covers such 

 more or less protected depressions with a rather close sod. This 

 condition is especially liable to arise if fires are prevented from 

 sweeping such habitats for a number of years. After a few years 

 of unrestricted vegetative development the sandy soil is covered 

 completely with an effective layer of leaf and stem litter and the 

 density of the stand is such that the most of the common interstitials 

 are prevented from entering the areas so controlled. The finely 

 divided refuse from several generations' growth may accumulate 

 to a slight depth over which there is, in the older and more protected 

 "pockets," a secondary tangle of straw and leaves. Refuse of this 

 sort affords a prime starting point for prairie fires. The treatment 

 of accumulated litter must of necessity be handled carefully, espe- 

 cially with reference to the management of plantations of forest 

 trees in the sandhills. At Halsey, Thomas County, where the 

 United States Forest Service is conducting extensive planting oper- 

 ations there is an area of a hundred acres or more that has not been 

 burned ov^r for at least ten years. Many of the numerous "pockets" 

 and "bottoms" that occur within this area show considerable litter 

 which has accumulated from the several generations of Panicum 

 z'irgatum and associated species. These conditions are scattered 

 here and there among the plantations of coniferous trees. The 

 question as to the future management of the plantations must con- 

 template the reduction of this inflammable material in order to rid 

 the plantations of the possibility of destruction by fire. Perhaps 

 the safest plan would contemplate the pasturage of the area in order 

 that the accumulation of inflammable vegetative refuse may be pre- 

 vented. Grazing is however attended by dangers which perhaps 

 might become nearly as destructive as fire. Stock might injure to 

 a serious degree the growth of the. trees. Then also too severe pas- 

 turage is liable to expose the soil of certain slopes to wind action 

 and consequent eradication of portions of the plantation because of 

 this force. An alternative might be found in firing the accumulated 



