e. Combination of Effects. By multiple regression analyses, environmental parameters 

 were tested for their contributions to the success or failure of transplants. The following 

 monthly measurements for each planting season were evaluated: (a) surface and subsurface 

 (six inches) soil salinity; (b) surface and subsurface (six inches) soil moisture percent; 

 (c) precipitation; (d) total available carbohydrates of bitter panicum, sea oats, and 

 shoredune panicum (percent); and (e) subsurface (4 inches) soil temperature and mean 

 temperatures for day and month of planting. Values used for the analyses are tabulated in 

 Table 26. 



The actual contribution of a particular environmental factor to the success of a grass 

 planting is difficult to interpret by this technique. Use of the technique to single out those 

 factors responsible, in combination, would be more significant. Multiple correlation 

 coefficients (R) and coefficients of determination (R 2 ) are tabulated in Table 27; 

 correlation coefficients (r) for individual factors are shown in Table 28. Correlation 

 coefficients (R and r) showing the relationship of environmental and parameters by season 

 of planting are in Table 29. 



These data showed that no one factor accounted for the success of a planting, and that 

 either extreme salinity or extreme drought could cause total failure. The other important 

 variables of soil temperature, air temperature, and plant vigor (as indicated by TAC in the 

 roots and rhizomes), contributed to planting success or failure but the data did not show 

 these variables responsible for a total stand failure, as for high salinity or lack of moisture. 



Apparently high sea oats survival after planting is partially dependent on high soil 

 moisture and low salinity at the surface and subsurface, and sufficient rainfall to keep the 

 soil moisture at a high level. Soil moisture less than 10 percent at a depth of 6 inches with 

 no more than 1 inch of rainfall during the month resulted in low plant survival, especially 

 during the more arid 1970-72 planting seasons. However, the 1972-74 planting conditions 

 were not as dry except on the south Padre sites where transplant survival also was influenced 

 by low moisture, but the relationship was less consistent. 



Salinity was a problem only if seawater covered the new transplants for extended 

 periods. Such occasions also left the soil high in salt content until sufficient rain reduced the 

 salt content to tolerable levels. Salinity levels increased during extended periods of low 

 rainfall, probably from salt spray, and this aggravated the drought stress on new transplants 

 since only the soil moisture and salinity factors often accounted for 100 percent of the 

 variation in sea oats survival (Table 27). 



Air and soil temperatures and carbohydrate storage were often important to sea oats 

 survival, but the time interval and location on the island indicated that these factors had no 

 consistent influence on survival. Correlation coefficients relating temperature to transplant 

 survival were mostly negative indicating that cooler temperatures were more optimum. 

 Surprisingly, liigh carbohydrate storage did not improve transplant survival and correlation 

 coefficients were mostly negative. 



