This trend of diminishing significance at the Boise Basin study area is in direct 

 contrast to the increasing significance for the 1964 plantings at Zena Creek. Approx- 

 imately one-third of the total variation in this Boise Basin test was caused by sam- 

 pling error, and only a negligible variation existed between experimental units (Areas) 

 This originally negligible variation increased with time, at a faster rate than treat- 

 ment variation, thus giving the opposite trend in "F" values. 



The interrelationships between the mulch temperatures on a day in August and soil 

 moisture relationships are not easily identified. The high temperatures that occurred 

 over the polyethylene apparently did not reduce seedling survival to any great extent 

 in this summer of abundant rainfall. Likewise, the slower recharge rate under this 

 mulch was not limiting to any noticeable degree. More moderate conditions associated 

 with the glass fiber blanket did not provide significantly better survival during the 

 5-year period. 



Indicating the advantages of less competition and earlier spring height growth 

 initiation, seedlings mulched with black polyethylene film were taller. As mentioned 

 earlier, significant numbers of the seedlings alive in 1968 had terminal damage 

 (table 6) . 



The impact of vegetative competition was evident and seedlings that received the 

 control treatment were the shortest in both terminal damage classes (fig. 9). A 

 comparison of the means within damage classes showed a significant difference (p = .05, 

 "t" test) only between the polyethylene and control treatments, and this difference was 

 in the "damaged" terminal class. Although the mean for the weeded treatment was the 

 same as the mean for the polyethylene the greater variation about the former made the 

 comparison with the control treatment insignificant (p = .05). These results imply 

 that the use of mulch to reduce competition does provide some increased height growth. 



Table 6. --Proportion (-peroent) of seedling terminals 

 damaged^ 1964 to 1968 



Treatment ' Area "A" ' Area "B" ' Average 



------- Percent ------ 



Polyethylene mulch 37 18 28 



Glass fiber mulch 20 32 26 



Hand weeded 26 37 32 



Control (no mulch) 35 60 47 



18 



