Drought has been shovm to be the major cause of mortality in early establishment 

 of ponderosa pine seedlings (Foiles and Curtis 1973; Pearson 1942; Rietveld and Heidmann 

 1976; Wagg and Hermann 1962). During this study, however, moisture stress was not 

 thought to be significant because of the abnormally high precipitation in June, July, 

 and August (table 2). Had the summer of 1975 been "normal" as far as rainfall, it is 

 likely that drought rather than cutworms would have been the leading cause of seedling 

 casualties . 



Initial Seedling Establishment 



Poor initial seedling establishment was due either to poor germination or to high 

 mortality. Treatment averages show that the opening plots produced the most surviving 

 seedlings (fig. 6). The opening treatments' 51.8 percent establishment was signifi- 

 cantly greater than the 22.5 percent establishment of the pine-influenced plots at the 

 1 percent level. 



Figure 6. — Fevoentages of 

 live seedlings after one 



growing season due to 



germination minus mortality ^ 



xoitln. statistical comparison 

 TREATMENT of treatments . 



15 



