1919 ^^99' ^^ ^^9 Succession 205 



as Douglas fir, western hemlock and giant cedar are fairly common in 

 them. 



We may look still further ahead to the time when this bog will, if 

 nature has her way undisturbed, reach a stage late enough so that the 

 forest will invade it as it has other Puget Sound bogs ; and to the final 

 occupation of the area by the climax forest (jDrobably hemlock) of the 

 region, the sphagnum bog being merely a temporary stage. 



The advance of bogs on sedge swamps 



Another type of bog development in this region is that in which 

 Sphagnum is encroaching upon a swamp characterized by an abundant 

 growth of rushes. Many Puget Sound bogs are bordered on one or more 

 sides by such swamps and the tension line between the two types of vege- 

 tation commonly represents an early stage of bog development. Such a 

 condition is found at the north side of Fauntleroy bog* just south of Seattle. 

 It was also present in several portions or the Mud Lake area just north 

 of Seattle before the draining of this lake, and is still found in several 

 portions of the bog at Poulsbo, Kitsap county, Washington. 



In these cases the Sphagnum may grow upon the ground among other 

 vegetation or in some cases it may find partial support from the rushes 

 and sedges. In the swampy northern portion of Graham lake, Maltby 

 bog is progressing by the growth of Sphagnum at the surface of the water 

 in and around the dense clusters of rushes. 



The fact that bunches of skunk cabbage (Lysichiton camtschatcense) 

 are common in bogs in this region seems to indicate that these bogs are 

 a later succession upon swamps. Each bunch of skunk cabbage occupies 

 a narrow but rather deep pit in the Sphagnum. Its survival from the 

 swamp stage to the bog stage and its final elimination by the latter with 

 the aid of mosses other than Sphagnum has been well described by Tures- 

 son (1916). 



The advance of bogs on open lakes 



Another type of bog development in this region is that in which the 

 bog is advancing upon the open water of a lake. In some eases the 

 Sphagnum with its typical flora of ericaceous shrubs borders directly upon 

 the lake. In a good many cases there is a lake in the center of the bog, 

 Sphagnum being dominant around its entire margin. Two such cases 

 have been examined by the writer. The largest of these is Crystal lake 

 in Maltby bog. This lake is somewhat circular in shape and has an 

 area of about 4 hectars (10 acres). Its border is not entirely regular 



* Nearly all of the Puget Sound bogs mentioned in this paper have been described (Rigg, 

 1913, 1917)'. 



