and interconnecting runners were then able to trap sediment and organic material, allowing it to 

 convert shallow open water to emergent marsh. 



Jointgrass tolerated short term exposure (3 weeks) to salinities of 14 ppt. Several ponds were 

 severely reduced in size by encroaching jointgrass. Burns conducted during periods of low water 

 were not successful in reopening ponds choked by invading jointgrass. 



Where aquatic vegetation reached the water surface, filamentous algae often formed surface 

 mats, smothering desirable aquatic plants. Prevost (1987) found that vigorous water circulation and 

 gradually increasing water levels helped prevent this problem. 



The encroachment of emergent perennial plants into shallow open areas of fresh and 

 intermediate marshes at LPWMA indicates that water level (drawdown) and salinity management 

 may be capable of stimulating revegetation of emergent wetlands. In deteriorated intermediate and 

 brackish marshes, the coverage of emergent perennials within four semi-impoundments at 

 Rockefeller Refuge has steadily increased in response to 28 years (1958-86) of drawdown 

 management. Furthermore, at Rockefeller Refuge, the most aggressive perennials are giant 

 cutgrass and various species of the genera Paspalum (Ted Joanen, Rockefeller Wildlife Refuge; 

 pers. comm.). Encroachment by giant cutgrass, bullwhip, and especially by jointgrass has also been 

 observed in response to drought (and prolonged periods of low water levels) in other intermediate 

 marshes of Cameron Parish, LA (Dr. Robert Chabreck, Louisiana State University; pers. comm.; 

 Bruce Lehto, District Conservationist, Soil Conservation Service, Calcasieu and Cameron Parishes, 

 LA; pers. comm.). Annuals and emergent perennials were found to close in and engulf ponds that 

 were dewatered annually in a Wisconsin marsh; therefore, it was recommended that drawdowns be 

 conducted only once every 3 to 4 years (Linde 1969). 



Germination of emergent perennial plants at Little Pecan Lake did not occur during extensive 

 drawdowns when pond bottoms were severely dried. Germination occurred most often when pond 

 bottoms were saturated or flooded to depths of only 2.5-5.1 cm. In moist-soil management areas, 

 which are dewatered annually, Miller and Arend (1960), Kadlec and Wentz (1974), and 

 Frederickson and Taylor (1982) found that germination of both annual and perennial plants was 

 severely reduced once saturated soils dried for more than several days. Summarizing published 

 literature, Kadlec and Wentz (1974) found that optimum conditions for the germination and 

 establishment of many annual and perennial wetland plants occur on moist soils or in very shallow 

 water. In greenhouse experiments, Weller (1975) found that when common cattail (Typha latifolia) 

 seeds were exposed to various water depths ranging from 2.54 to 50.8 cm, germination occurred 

 more readily at depths between 2.54 and 15.2 cm. In the field however, Beule (1979) observed 

 that in the vast majority of cases, germination of common cattails occurred on exposed mud flats. 



Encroachment by emergent perennial plants at LPWMA occurred primarily through vegetative 

 propagation during periods of low water when pond bottoms were either saturated or flooded to 

 depths of only several inches. Similar effects have been observed by others (T. Joanen, pers. 

 comm; R. Chabreck, pers. comm.). In greenhouse experiments, common cattails produced nearly 

 twice as many rhizome shoots at water levels less than 15.2 cm versus water levels greater than 15.2 

 cm (Weller 1975). In coastal marshes of Louisiana, increased water levels have been found to 

 reduce survival, growth, and productivity of wetland plants (Salinas et al. 1986). Without a period 

 of low water, stands of emergent perennial vegetation in northern freshwater marshes have been 

 observed to decline. When these areas were dewatered, however, a remarkable rejuvenation of 

 perennial vegetation was observed (Kadlec 1962; Linde 1969; Kadlec and Wentz 1974). 



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