Drainage can be effected by cutting 

 drainage ditches some 30 inches 

 wide and deep to lead the water 

 from the denuded spots. The use 

 of blind or closed ditches prevents 

 the intrusion of sea water in coastal 

 marshes. After the areas have been 

 satisfactorily drained, the ditch 

 ends should be closed to raise the 

 water levels again, or the marsh 

 may be seriously damaged. Ex- 

 treme care must be exercised in 

 ditching a marsh so as not to alter 

 the water relations and thereby 

 favor invasion of the marsh by un- 

 desirable vegetation. 



Increasing the food supply 



On marshes having water-control 

 structures it is often possible to in- 

 crease the supply of desirable musk- 

 rat food plants by manipulating 

 water levels. Many undesirable 

 plant competitors can be controlled 

 by raising the water level a few feet 

 and maintaining it for several 

 months. The areas opened up by 

 killing off noxious plants should 

 then be planted, preferably in the 

 spring, with such food plants as the 

 cattails {Typhu glauca, T. lati- 

 folia)^ the three-square bulrushes 

 {Scirpus olneyi^ S. americarms) , 

 saltmarsh bulrush {S. rohiostws), 

 and the hardstem bulrush {Scirpus 

 acutit^ ) . Pieces of roots with buds 

 attached are transplanted into the 

 muck at the edges of the impounded 

 areas. The two exotics, water- 

 hyacinth {Eichhornia crassipes) 

 and alligatorweed {Altemanthera 

 philoxeroides) have become estab- 

 lished in recent years in the coastal 

 marshes of Louisiana ; and despite 

 numerous attempts to control them 



Figure 20. — Beneficial effect of burning 

 "three-square" bulrush is apparent in 

 this Maryland marsh, control-burned 

 in February ; on May 22 the burned- 

 over areas were in full bloom, while 

 new growth in the small, unburned 

 part adjacent to the shell road (left) 

 was just emerging. 



by various mechanical means or by 

 spraying with weed killers, they are 

 fast clogging the extensive network 

 of canals and bayous. In certain 

 localities these weeds have increased 

 to such an extent that they almost 

 dominate the native plants. While 

 water-hyacinth is scarcely touched 

 by the muskrat, alligatorweed at 

 times is used to a considerable ex- 

 tent, and in the Mississippi area 

 often forms as much as 15 percent 

 of the muskrat's diet. 



Fire is an imjjortant factor in the 

 ecology of any marsh, and con- 

 trolled burning is an accepted tool 

 in marsh management. It must be 

 recognized, however, that a certain 

 amount of cover is essential to pro- 

 tect the muskrat from its enemies. 

 To the trapper in the old days burn- fl 

 ing merely meant easier trapping ' 

 and more three-square. Marsh 

 burning is beneficial in that it de- 

 stroys the "rough" and prevents 

 elevation of the marsh through peat 

 accumulation (fig. 20). 



14 



