Sphagnum moss is strikingly different from all other mosses in its structure and its influence on the growth of other plants. Both its leaves and its stems contain many large "hyaline" cells, which consist of cell walls only, and have no living contents when mature. The walls of these cells have pores which facilitate the entrance of water, and large quantities of it are thus taken in and retained by this moss. When Sphagnum forms a dense mat, it tends to encourage the growth of certain plants (e. g. some heath shrubs) and to discourage the growth of many of the plants common in the region. Its presence thus tends to produce a "bog flora". This is very striking where Sphagnum moss has formed a thick continuous mat over a considerable area, but is less evident where the lay of Sphagnum is thin and where it occurs in small patches only.
Sphagnum flourishes in cool places which are very wet during the growing season, and is most common on flat areas from which there is little or no drainage. When it once gets a start in such a place it encroaches rapidly on other vegetation. It forms extensive bogs with very characteristic flora in the low lands of the Puget Sound region and occasionally up to 3000 feet elevation, or even a little higher, in the Cascade mountains. In the Olympics its occurrence is somewhat similar to that in Mt. Rainier National Park.
Sphagnum moss is known to occur in Mt. Rainier National Park in the following places: Berkley Park, Mystic Lake, Lake James, Windy Gap, Mowich Lake, Eunice Lake, and Mountain Meadows. It probably occurs in other places also, but it seems evident that the places listed show representative habitats for Sphagnum in the Park.
In Berkley Park two small species of Sphagnum (S. teres and S. robustum) are growing vigorously in small patches 5 to 15 feet in diameter on a flat sedge meadow (elevation about 5700 feet) having an area of about 2 acres. Some of these patches are flat on the meadow, some have grown into low hummocks and some extend along the margins of small rivulets. The rugged slopes of Berkley Park rise abruptly on the east and west sides of this meadow and a small stream flows through it to the north fork of the White River. This meadow is very cool and wet since it lies immediately north of Mt. Rainier and Burroughs Mountain where it receives much drainage water and comparatively little sunshine.
The living Sphagnum has about 8 inches of dead Sphagnum under it, indicating that it has flourished there for a good many years. Under the dead Sphagnum are sedge peat and muck. The Sphagnum is everywhere encroaching on the sedge meadow and if nature is allowed to take its course it will probably in time form a continuous Sphagnum bog. At present the only plant growing in the Sphagnum and not in the sedge meadow is a small variety of swamp laurel (Kalmia microphylla). Plants common in the living Sphagnum and also in the sedge meadow are two heathers (Phyllodoce empetriformis and Cassiope Mertensiana), a small red spiraea (S. densiflora), a huckleberry (Vaccinium sp), a small blue gentian (Gentiana calycosa), a bright yellow Potentilla (P. flabellifolia), a lousewart (Pedicularis surrecta), a pink fleabane (Erigeron salsuginosus), a white flowered lovage (Ligusticum purpureum), a marsh marigold (Caltha leptosepala), a small sedge (Carex sp), an unidentified grass, an unidentified moss, and two unidentified toadstool fungi. These patches of bog thus represent a very early stage in bog succession, and the selective influence of the Sphagnum on their flora extends to only one species.
The occurrence of Sphagnum at Mytic Lake is similar to that in Berkley Park. It grows in patches on a swampy flat bordering the south side of the lake which is on the north side of Mount Rainier at an elevation of about 5300 feet. There are, however, the following differences. (1) The individual patches are larger. (2) The total area of Sphagnum on the flat is larger. (3) The layer of dead Sphagnum is a little thicker. (4) There is a little more evidence of selective influence of the Sphagnum on the plant society occurring in it. This selective influence includes four species. The swamp laurel is common in the Sphagnum and within a few feet of it, but not elsewhere in the swampy meadow. The crowberry (Empetrum nigrum) is abundant in the Sphagnum, but not outside of it in the immediate vicinity. When seen elsewhere in this portion of the Park (e. g. on Tyee Peak) it was on rocky, drier places and was bearing berries abundantly, though no berries were found on it in the Sphagnum. A small fireweed (Epilobium sp) was much more abundant in the Sphagnum than elsewhere. Very small stunted specimens of the lodge pole pine (Pinus contorta) were found in the Sphagnum, but this species was not found elsewhere in wet places, though it was abundant on nearby higher places. It thus appears that the Sphagnum succession on the wet sedge meadow has reached a little later stage at Mystic Lake than it has in Berkley Park.
The Sphagnum in Mountain Meadows like that in the two cases just described is an early stage of succession on a very wet sedge meadow. These meadows are crossed by the old Grindstone Trail and lie between Mowich Lake and Grindstone. The patches of Sphagnum occur in the margins of the meadows. Two plants (Kalmia microphylla and Gaultheria humifusa) occur in the Sphagnum but not elsewhere in the meadow, though the latter is in the woods nearby.
The Sphagnum at Windy Gap is less than an acre in extent and is fairly continuous. It occupies a rather poorly drained area at an elevation of about 5700 feet. The occurrence of swamp laurel and crowberry here in Sphagnum but not elsewhere in the immediate vicinity is like that at Mystic Lake.
The Sphagnum at Lake James, Mowich Lake, Eunice Lake, and along the trail between Mowich Lake and Mountain Meadows is small in amount. It grows over soil, logs, and stumps and exercises no selective influence on the plants growing with it. The Sphagnum in Berkley Park was studied in August, 1934. In the other locations it was studied in 1922 and preceding summers.
Dr. Geo. B. Rigg,
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