and old transects were sampled so that in August 1987 a total of forty 0.25-m 2 plots had 

 accumulated and were clipped of vegetation. 



Throughout the study, the sites were surveyed for any new plant colonizers. Voucher collections 

 were made and deposited in the Herbarium of Tulane University, New Orleans, LA. 



RESULTS 



At the start of this study (1984) the sites had an exposed (at mean sea level) mudflat area of 

 approximately 5,000 m 2 . By the summer of 1985, about 30,000 m 2 of new land had accreted and 

 had been vegetated. Currently (spring, 1988) over 60,000 m 2 of land has developed and has been 

 colonized by vascular plants. 



Sedimentation rates vary tremendously and are dependent upon annual flood and sediment load 

 cycles. Rates per site varied from 8.4 cm/4 mo to as little as 0.2 cm/5 mo. The average rate was 

 0.0189 cm/d for 3 years or 6.9 cm/yr. Typically the most rapid sedimentation occurs seasonally 

 during spring floods. When flood waters recede (April-May) large newly developing mudflats are 

 left exposed, particularly during low tides. 



A total of 62 plant species from 21 families have been collected and identified from the accreting 

 flats (Table 1). The graminoids (grasses and sedges) comprise the largest number of species (21), 

 of which Scirpus deltarum (delta three-square grass) is the most common. The only woody species 

 is Salix nigra (black willow). 



Primary plant colonization is very rapid on the exposed mudflats. By the end of £he f irs t 

 summer, 133 g/m 2 of aboveground plant biomass were present. Two species predominated: 

 Sphenoclea zeylanica on the lower flats and Salix nigra (14 g/m 2 ) on the highest flats. Two 

 graminoids were common; usually they occurred along with several other species: Eclipta alba, 

 Lindemia dubia, Ammania coccinea, and Cyperus difformis. 



By the end of the second summer (12 months after colonization) 553 g/m 2 of plant biomass 

 were present. At this time Scirpus deltarum had colonized the mudflats with an average biomass 

 of 55 g/m 2 . Scirpus deltarum, along with several other sedges (Cyperus erythrorhizos, Cyperus 



Table 1. Plant species (by family) collected at three sites on developing splays within the Delta 

 National Wildlife Refuge. 



ALISMATACEAE 



Alisma subcordatum Raf. 

 Sagittaria platyphilla Engelm. 

 Sagittaria graminea Michx. 

 Sagittaria latifolia Willd. 



AMARANTHACEAE 



Acnida cuspidata Sprengl. 

 Amaranthus tamariscina Nutt. 



ARACEAE 



Colocasia esculenta (L.) Schott 



CAMPANULACEAE 



Sphenoclea zeylanica Gaertn. 



(Continued) 

 52 



