spring tides and storms, but not by daily lunar tides. The vegetation 

 is dominated by short Spartina alterniflora with Distichlis spicata 

 and Salicornia spp. present in small numbers. Small areas of typical 

 low marsh, dominated by tall S. alterniflora , exist near the inlets 

 and in a narrow band along the bay shore subject to regular flooding. 



The estimates of maximum standing crop of dry material and organic 

 matter were recorded based on the results of sampling in August. The 

 greatest variability was in the samples of short Spartina alterniflora , 

 with a minor contribution by tall S. alterniflora . Generally, 

 production per unit of various species decreases from south to north 

 along the Atlantic Coast. Marsh plants from areas in which there were 

 large standing crops had the same percentage composition as plants 

 from areas with small standing crops, indicating that the inorganic 

 nutrients measured were probably not limiting production. (L.H.) 



Keywords: primary productivity, Spartina alterniflora (short), 



Distichlis spicata , Salicornia spp. , Maryland-Virginia 



II-B-27 



Cahoon, D.R. 1975. Net productivity of emergent vegetation at Horn Point 

 salt marsh. M.S. Thesis. University of Maryland. 94 pp. 



Analyses of monthly standing crop, daily rates of production, and 

 variations in yearly productivity for five major vegetation zones, 

 and estimations of underground production for the Spartina patens/ 

 Distichlis spicata mixture were conducted over two consecutive 

 growing seasons for a Chesapeake Bay brackish marsh. Regression 

 models for plant height and dry weight biomass were generated for all 

 seasons of the year, and covariance analysis demonstrates that the 

 relationship between height and dry weight within each species is 

 the same for all seasons of the year except in the species Spartina 

 alterniflora and Phragmites austral is . Positive correlation coefficients 

 ranged from 0.2 for S^ alterniflora to 0.96 for P^ austral is with the 

 other species having intermediate values. Overall, production at 

 Horn Point is lower than most other values in the„literature with the 

 2-year average value for S. alterniflora (676 g/m ) being one-half the 

 average for the Atlantic coast, but with the 2-year average for S. patens 

 (628 g/m^) being slightly higher than that of the Atlantic coast. 

 On a square meter basis, the primary producers rank in the following 

 order of importance for the two-year average of standing crop: Typha 

 angusti folia (985 g/m2), Phragmites austral is (892 g/m2), S. alterniflora/ 

 Amaranthus cannabinus (676 g/m2) , S. patens/D. spicata (628 g/m2) 

 and Hibiscus moscheutos (516 g/m2). However, the most important zones 

 in terms of areally weighted production (in metric tons) for 1973 at 

 Horn Point Marsh are the S. patens/D. spicata (7.61), H. moscheutos 

 (5.07), S. alterniflora/A. cannabinus (3.22). P. austraTis (0.659), 

 and T^ angustifolia/ H. moscheutos (0.644). 



54 



