Table 5« — Relative abundance of seedbed types 



Seedbed type Percent of 



clearcut area 



UncOTipacted mineral soil 19 



Disturbed organic layer 18 



Undisturbed moss-covered surface 17 



Moderate slash 15 



Rotten wood 13 



Dense slash 9 



Moderate Vaccinium over undisturbed moss 4 



Dense salmonberry and Ribes brush 2 



Road and right-of--way 2 



Compacted mineral soil 1 



Dense herbs less than 1 



Grass or sedge sod less than 1 



Extreme temperatures in the environment of se p(i^„-inp;5y 



It was noted in the 1954 annual report that high surface temperatures 

 had been observed on undisturbed, moss-covered organic layers in 

 clearcut areas. These observations, vriiich were of a preliminary 

 nature, indicated that temperatures in excess of 120° F, occurred on 

 this type of seedbed. Germination and survival of seedlings on these 

 undisturbed seedbeds appeared poor canpared to a seedbed in which the 

 mineral and organic layers had been mixed. Poorer germination and 

 s\irvival were attributed to high surface temperatures which depleted 

 available moisture. 



In carrying these investigations further a record was taken of the 

 near-surface temperature extremes and their effect on seedling germina- 

 tion and survival on both undisturbed and mixed-soil seedbeds, Max,- 

 Min, thermometers were installed at 1-inch above the soil surface, at 

 the surface, and 1-inch below the surface to permit recording of daily 

 extreme temperatures. These two seedbed types were also seeded with 

 equal quantities of Sitka spruce, western hemlock, and western redcedar. 



The magnitude of extreme temperature differences between imdisturbed and 

 mixed seedbeds is shown by the seasonal march of 6-day means in fig, ?• 

 Dissipation of incoming and outgoing heat in the soil is principally 

 responsible for temperature differences between the two seedbeds; heat 

 is more easily conducted through the tightly packed mix:ed soil than 

 through the loosely packed organic soil. Maxima greater than 100° F, 

 were frequently encountered at the surface of the undistijrbed soil. 

 The highest observed was 130° when air at 3 feet in the open reached 

 84°, By means of regression (analyses) it was shown that temperatures 

 higher than 120° can be anticipated on vindisturbed surfaces -when air 

 at 3 feet reaches 80°, Surface temperatures reach about 138° when air 

 temperature is 90°, Climatological records indicate, however, that 

 air temperature extremes higher than 85° are rarely encountered in 

 Southeast Alaska, In contrast to the -undisturbed surface, maxima 

 higher than 100° were infrequent on the mixed seedbed, 



- 21 - 



