strigosus, Cyperus difformis, Cyperus aristatus, and occasionally Cyperus surinamensis; total biomass 

 equals 157 g/m 2 ), dominated the mudflat. The black willow (Salix nigra) had grown to 87 g/m 2 by 

 the second summer's end. 



Twenty-four months after colonization or by the end of the third summer Scirpus deltarum 

 increased tremendously in importance to 483 g/m 2 , comprising nearly 50% of the 1,098 g/m 2 total 

 aboveground biomass. Also, the formerly abundant Cyperus species declined considerably and were 

 replaced by the numerous grasses listed in Table 1, of which Panicum dichotomiflorum, Leptochloa 

 panicoides, and Echinochloa walteri are the most abundant. Salix nigra continued to increase in 

 biomass to 167 g/m 2 . 



At the head (upstream end) of the developing mudflats (islands), Salix nigra dominated from the 

 start. However, browsing of the willow by nutria and deer can greatly retard the willow's potential 

 for long-term local dominance. Some areas were heavily browsed to the virtual elimination of 

 willow, and various herbs became established in the years after initial colonization. After several 

 years, within these heavily browsed regions of the splays, the assortment of herbs was less diverse 

 and eventually the browsed areas became dominated by Scirpus deltarum. 



By the end of the fourth summer, the direction of secondary plant succession was clearly toward 

 two perennials: Scirpus deltarum on the lower and heavily browsed higher flats and Salix nigra 

 on the less browsed higher flats (Figure 2). By this time the total aboveground biomass was 1,194 

 g/m 2 of which 600 g/m was Scirpus deltarum and 222 g/m 2 was Salix nigra. Other sedges, grasses, 

 and herbs had a combined total of only 257 g/m 2 . Monotypic stands of Colocasia esculenta 

 (elephant ear) were found on portions of the Octave Pass and Brant Pass splays where very fine 

 silt had been deposited. Usually these stands were adjacent to and down flow from stands of 

 Salix nigra (Figure 2). 



Throughout this successional process, the total amount of belowground organic material increased 

 to 1,212 g/m 2 by 36 months after colonization. Most of this material was living roots and rhizomes 

 of Salix nigra and Scirpus deltarum. 



DISCUSSION 



If one takes into account that this study was restricted to splays, well removed from uplands and 

 dredged spoil, the plant species on the developing mudflats within the Mississippi River Delta are 

 not significantly different from those described by Montz (1978) for the Atchafalaya Delta or from 

 Howard and Penfound's (1942) description of areas of sedimentation from crevasse formation in 

 the Bonnet Carre floodway on the Mississippi River above New Orleans. Of the 62 species of 

 vascular plants identified from the three sites, only 14 incidentals were not listed by Montz (1978). 



Quantitatively, however, the composition of the vegetation on the developing splays at the 

 Mississippi River Delta is quite different from similar areas in the Atchafalaya River Delta. 

 According to Johnson et al. (1985), the developing islands there are dominated by Salix nigra at 

 their heads, and vast areas of Sagittaria latifolia make up the majority of the remaining vegetation. 

 Between these two community types exists a relatively small area of a Typha latifolia community 

 and pockets of a "seasonal" community of several species, including Cyperus difformis, Eleocharis 

 parvula, Ammania coccinea, and Sphenoclea zeylanica. 



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