The productivity of plants, referred to as primary production, is the 

 rate at which the energy of sunlight is captured and used to build plant 

 tissues upon which all consumer organisms are ultimately dependent. Primary 

 productivity may be determined by measuring changes in oxygen, carbon 

 dioxide, pH, or available raw materials; by using radioactive tracers; or 

 by determining chlorophyll content and assimilation ratio. Primary pro- 

 duction of vascular plants in marshes is usually measured by the harvest 

 method, in which estimates are made of the increase in plant biomass during 

 the growing season (Keefe 1972). The procedure involves the harvesting of 

 plant samples periodically during the growing season. Modifications of this 

 method take into consideration life history and phenology of the plant, as 

 well as sampling procedures. These modifications have enabled investigators 

 to arrive at more reliable productivity values (de la Cruz 1977). 



The amount of information on the primary productivity of tidal coastal 

 marshlands has increased steadily during the last decade. Data summarized 

 by investigators show production values ranging from 500 to 1000 grams of 

 dry weight per square meter for the short form of the smooth cordgrass, 

 Spartina alterniflora ; 1100 to 3000 g dry wt/m^ for the tall form of 

 $. alterni flora ; 500 to 2000 g dry wt/m^ for the black needlerush, Juncus 

 roemerianus ; 1000 to 2200 g dry wt/m^ for the giant cordgrass, S^. cynosuroides; 

 and 993 to 1922 g dry wt/m2 for the wire grass, ^. patens (de la Cruz 1977). 

 From these data, it is apparent that the primary production of marsh angio- 

 sperms varies widely from several hundred to a few thousand grams of dry 

 organic biomass per square meter. Although this variability is believed 

 to be due to the types of plant species involved, salinity and hydrology 

 of the habitat, geographic latitude and temperature, and sampling method- 

 ology, a definitive study has not yet been made to demonstrate the influence 

 of one or more of these parameters. There are indications that the marsh 

 plants in the lower latitudes are not only bigger than their counterparts 

 in the higher latitudes, but also more productive. 



Until very recently, most of the studies concerning the primary pro- 

 duction of coastal marshes were concerned only with plant shoots (or aerial 

 parts), presumably because of the difficulty in sampling roots and rhizomes 

 (or subterranean materials). The few studies available on below-ground 

 productivity show annual production values ranging from 450 to 2500 g dry 

 wt/m^ for tne short form of S. alterniflora ; 500 to 3500 g dry wt/m2 for 



the tall form of S^. alterniflora ; and 1360 g dry wt/m for Juncus roemerianus 



(de la Cruz 1977). From these values, it is apparent that total production 



of marsh vascular plants is approximately double that previously reported for 

 emergent materials. 



VI 



