Table 5.4. Effects of irrigating the cordgrass marsh in situ (from Zedler, Beezley, 

 and Beare unpubl.). 



Block 



Watering treatment 3 

 Control Yr-Long Winter Summer 



Jan. -June Increase 

 in Total Stem Length 



(cm/0.125 m 2 ) 



Jan. -June Increase 

 in Mean Height (cm) 



Jan. -Aug. Increase 

 in Mean Height (cm) 



Jan. -June Density 

 Change (#/0.25 m 2 ) 



June-Aug. Density 

 Change (#/0.25 m 2 ) 



a Watering began January 9, 1984, and continued approximately biweekly through 

 August 7, 1984; winter watering ended and summer watering began on May 31; 

 control plots were unwatered. Drought affected all plots from July onward. 



cordgrass mortality in the last 5 weeks of the 

 experiment, when soils dried out between 

 waterings. However, one control plot 

 increased in density. While evidence is 

 scanty, there is at least a suggestion that 

 infrequently wetted areas withstand drought 

 better, and differential rooting depths might 

 explain differential survival. Studies of 

 below-ground plant growth at different 

 intertidal elevations are needed to explain the 

 high creek-edge mortality seen during the 

 1984 drought. 



The importance of seedling recruitment 

 was not addressed in these year-long 

 experiments. Most of the dynamics of 

 cordgrass have resulted from changes in 

 vegetative growth. 



5.4.2 Manipulation of Inundation in 

 Outdoor Mesocosms 



Griswold (1988) investigated the effect of 

 inundation using meter-square mesocosms 

 within a field research facility at Tijuana 

 Estuary. Cordgrass and pickleweed growth 

 were each examined in relation to inundation 

 levels. Six rows of cordgrass were planted 

 along a slope in nine mesocosms; six rows of 

 pickleweed were planted in another 9 

 mesocosms; and water levels were maintained 

 to inundate the lower two rows. Thus, the 

 lower rows were saturated, the middle two 

 rows were relatively moist (26-27% soil 

 moisture) and the top two rows relatively dry 

 (22-23% moisture). Surface soil salinity 

 varied along with soil moisture, with the 

 lower rows ranging from 15-20 ppt, middle, 



1 1 2 



