RATE OF GROWTH IN SPHAGNUM BOGS 729 



The western dogwood, an aspen (Populus tremuloides Michx.), and 

 a crab-apple (Pyrus rivularis Bong.) are found in the marginal ditch 

 of some bogs ; but the writer has not found any of these species, except 

 the dogwood, present in the actual bog stage in any case. A few speci- 

 mens of this dogwood occur in the Green Lake bog. 



The advance of forests on Puget Sound bogs is very slow and the 

 individual trees that have obtained a foothold are much stunted by the 

 bog conditions.* Their growth in both height and diameter is very 

 slow. 



The writer's data on the rate of growth of trees outside of bogs were 

 secured mainly from logged-off lands where natural reforestation is 

 going on. The region in the vicinity of Silverdale in which many of 

 the observations were made is hilly and the soil is stony and infertile. 

 It is very dry in summer. 



The counts and measurements in all habitats were made at a height 

 of lO to 15 cm. (4 to 6 inches) from the base of the tree except in the 

 case of very small specimens. In these the measurement was at the 

 very base. In the case of trees growing in sphagnum, it is often diffi- 

 cult to determine the location of the base of the tree exactly without 

 actually pulling up the tree. 



In the field-work the trees were cut close to the base and a short sec- 

 tion of the stem was cut off and taken to the laboratory, where the end 

 was smoothed with a knife and the annual rings counted with the aid 

 of a hand lens. In the case of very small stems a razor section was 

 prepared and the count of rings was made under a compound micro- 

 scope. In all, data were secured from 63 trees growing in sphagnum 

 and 61 in other habitats. 



Leaving out the detail of measurement for lack of space, the average 

 annual rate of growth in bogs and outside of them is summarized in 

 the following table : 



Average Grozvih of Conifers in Bogs and Outside of Them 



A. Diameter 

 Species In bogs Outside ^f^^og' 



No. mm. No. mm. 



Western hemlock 13 i.oi 7 1.56 64 



Western white pine 9 .78 II 1.34 58 



Giant cedar 11 .60 6 1.15 52 



Lodgepole pine 9 .78 21 1.57 49 



Douglas fir 21 .86 16 1.69 40 



*For discussion of bog conditions, see Rigg, G. B. : "A summary of bog 

 theories." PI. World 19:310-325, 1916, and the literature there cited. 



