increase soil moisture in the vicinity of planted seedlings looked promising. Accord- 

 ingly, two new mulching materials (black polyethylene film and a light-colored glass 

 fiber blanket) were chosen for testing and comparison with a no-mulch (control) 

 condition. 



The two synthetic mulch materials were in sheet form, rolled for shipment. The 

 polyethylene was 4 mils thick, 36 inches wide and 150 feet long and was perforated every 

 3 feet to facilitate separation. The glass fiber blanket was 1/4 inch thick, 6 feet wide, 

 and 150 feet long and had to be cut into 3- by 3-foot pieces. 



East and west aspects were compared. All six plots were located on soils that aver- 

 aged 20 to 40 inches deep. Sample soil depths, from surface to bedrock, ranged from 

 12 to 43 inches. 



In the fall of 1962, 900 spots 36 inches square were first scalped and then dug 

 out to form a pit of sorts. The pits were allowed to settle during the winter. In 

 early April, 1963, the 150 pits in each of the six plots were planted with a 2-0 ponder - 

 osa pine seedling (fig. 4). The three treatments were randomly assigned within groups 

 of three adjacent seedlings. Late in May the two kinds of mulch sheets were spread 

 around designated seedlings and held in place with three to five wire pins (fig. 5). 

 For a total of 50 trees the cost per tree for mulch and installation was : polyethylene- 

 42 cents; glass fiber-66 cents. 



Temperatures were measured in early August 1963, at the mulch surface and at the 

 soil surface under the mulch (table 3). The dates and time of day were selected to 

 provide the highest temperature readings for each aspect. Surface temperatures were 

 generally the highest on the black polyethylene; temperatures on the glass fiber sur- 

 face were consistently the lowest. Soil temperatures beneath mulches were 13 to 18 

 degrees less than on the mulch surface, and 14 to 24 degrees less than at the exposed 

 soil surface. No heat lesions were found on seedling stems in contact with mulches. 



Mulch differences were highly significant in the analysis of variance for sur- 

 vival for 1963 through 1967. Survival was best with a glass fiber mulch (Appendix II). 

 It seems that competition on the "check" plots increased in this 3-year period while 

 with black polyethylene the competition was maintained at a reduced level. Some 

 increased first-year transpirational stresses over the warmer black polyethylene may 

 have caused the initial high mortality. With increasing age and height this factor 

 would have less influence and competition factors would become more important. Fifth- 

 year survival percentages were: 



Treatment East West 



(Feroent) 



Control (no mulch) 16.1 31.1 



Glass fiber mulch 43.3 47,9 



Polyethylene mulch 22.0 30.1 



The aspects tested (west and east) did not have a significant effect on survival 

 rate. Survival on individual plots during the first year ranged from 98 percent for 

 seedlings mulched with glass fiber on the east aspect to 24 percent on the same 

 aspect with black polyethylene. Furthermore, the interaction between aspect and mulch 

 was not significant. 



Although mulch materials did not completely eliminate vegetative competition, they 

 did slow it down, and at many of the installations the effect continued into 1969. 



7 



