density (24%) and height (23?) of 

 cordgrass (Zedler 1981c and unpub. ms.b). 



At Mugu Lagoon, Onuf et al, (1981) 

 reported stimulation of pickleweed growth 

 following flooding and sedimentation in 

 both 1978 and 1980, with a return to 

 pre-flood conditions during 1979. The 

 first response to flooding was a 71? 

 increase in biomass of green growing tips 

 at the time of the 1978 peak standing 

 crop. The second response was a 31? 

 increase in the same measurements (Onuf, 

 pers. comm.). 



These field responses to flooding 

 support laboratory results that 

 hypersalini ty reduces salt marsh plant 

 growth. And the range of values for 

 cordgrass over recent years shows that one 

 year's measurement is not sufficient to 

 assess the "productivity" of southern 

 California coastal marshes. There is a 

 high degree of variability in both 

 environmental characteristics and 

 halophyte productivity. 



2.9 DECOMPOSITION OF VASCULAR PLANTS 



Determining what happens to the 

 vascular plant material which is produced 

 in the marsh is difficult. It may be 

 consumed by animals, broken off and 

 transported to some other area by winds or 

 tides, or it may decompose or accumulate 

 on the site. The latter process is 

 easiest to follow, because portions of 

 plants can be collected and known amounts 

 placed in litter bags (usually these are 

 mesh with 2-mm openings) . Bags can be 

 tethered in selected locations and 

 reweighed later. As decomposition occurs, 

 large pieces of plant material are 

 gradually reduced in size by mechanical 

 and biological forces, until the material 

 moves out of the litter bag. Loss rates 

 are usually exponential, that is, the 

 greatest change occurs in the first few 

 weeks, as soluble compounds leach from the 

 plants and as consumers (fungi, bacteria 

 and herbivores) utilize the most 

 digestible portions. The remaining plant 

 material is progressively less susceptible 



to digestion or leaching, and loss rates 

 decline. Ultimately, with complete 

 mineralization of the plant parts, the 

 organic matter is converted back to carbon 

 dioxide, water and nutrients, which are 

 then available for reuse by other plants. 



Several factors influence 

 decomposition rates in southern California 

 salt marshes. In a comparative study, 

 Winfield (1980) found that plant type, 

 location of litter bags, and type of 

 decomposers all influence loss rates at 

 Tijuana Estuary. Succulents and cordgrass 

 ( Spartina foliosa ) leaves decomposed more 

 rapidly (9?/mo) than the more fibrous 

 cordgrass stems (7J/mo) when litter bags 

 were placed at approximately mean high 

 water. Litter bags placed in tidal creeks 

 and middle marsh habitats all had higher 

 decomposition rates than bags placed in 

 the higher, drier habitats. The lowest 

 rate (3?/nio) was for the fibrous 

 shoregrass ( Monanthochloe littoralis ) 

 placed in its usual high marsh location. 

 The highest rate (33?/n'o) was for dead 

 leaves of cordgrass placed in a tidal 

 creek, where several factors were 

 conducive to decomposition. Moisture was 

 usually high and nitrogen (especially 

 ammonia) was available to enhance 

 microbial growth. Crab larvae settled in 

 the bags and their shredding and feeding 

 activities further hastened plant losses. 



From these results and the 

 information on plant productivity, it 

 becomes obvious that salt marsh 

 functioning is strongly influenced by 

 tidal circulation. The tides are 

 responsible for physical, chemical and 

 biological events which are important to 

 the growth and decomposition of vascular 

 plants and, as the next chapter shows, to 

 the understory algal mats as well. 



2.10 SUMMARY OF CHAPTER 2 



Southern California coastal marshes 

 are dynamic in both structure and 

 productivity. The halophytes have broad 

 ranges of tolerance for the conditions 

 associated with the one meter intertidal 



42 



