Wetlands with Intermingled Forests
This association is confined to riparian areas, seeps, and fens. Precipitation ranges from 25 to 70 inches per year, occurring mainly as snow. The average annual temperature is very cold (38 to 42 degrees), and the growing season is very short (less than 70 days).
The riparian areas along Annie Creek, Sand Creek, and the Rogue River commonly are at the contact with the older, buried glaciated sediment present before the latest eruptions of Mount Mazama. Precipitation filters down through sometimes hundreds of feet of volcanic ash, comes into contact with the much less permeable glaciated sediment, and then moves laterally, eventually surfacing as springs, seeps, and riparian areas.
All of the ecological sites in this association are influenced by a fluctuating water table, varying degrees of an anaerobic condition, and generally thick-surfaced organic soils (35 to 70 inches deep or more to mineral soil). The wetlands at the headwaters of National Creek and at Sphagnum Bog are fens that are characterized by a high water table, an accumulation of peaty organic matter, and low availability of nutrients. The nutrient supply for fens is primarily provided by precipitation, surface water, and groundwater, whereas the nutrient supply for bogs is provided by precipitation only (Aerts, 1999; Johnson and others, 1995; Radforth and Brawner, 1977).
The fens in this association support two distinct historic climax plant communities. Studies have shown that the accumulation of organic matter on the surface from litter and windthrown trees affects the characteristic plant community. Brock suggested that peat hummocks accumulate on top of the organic soil surface in the absence of fire, but in dry, hot years the hummocks are consumed by fire, leaving the saturated organic soil surface (Dorr and others, 2000). An accumulation of peat 4 to 6 inches thick is sufficient for tufted hairgrass and sedges to root above permanently saturated layers. An accumulation of more than 6 inches allows for colonization of blueberry, alder, and willows. Lodgepole pine can grow in accumulations of 16 inches or more. There is also some evidence that conifer litter has an allelopathic effect on mosses, meaning mosses are killed by the accumulation or decomposition of this litter.
The ecological sites in this association are located only along the boundary in the west-central part of the park, in the Poison Meadow area. These sites have a greater influence of glaciated sediment, and they may be present in larger areas at lower elevations in the adjacent Rogue River and Winema National Forests. These sites have either an aquic soil moisture regime and support dominantly sedges or a udic soil moisture regime and support dominantly grasses. All of the ecological sites in this association have cryic soil temperatures.
The Meadow Fen ecological site is along perennial streams and the edges of the wetter fen sites. Some areas of this site have relatively deep accumulations of rubbed fibers and mucky peat soils with a layer of ashy sand in the subsoil. This site supports dominantly lush stands of water sedge (Carex aquatilis) and smaller amounts of bluejoint reedgrass (Calomagrostis canadensis) and arrowleaf ragwort (Senecio triangularis). It has a sparse canopy of lodgepole pine. It occurs in association with the Sphagnum Fen ecological site.
Lodgepole pine (Pinus contorta)/Shasta red fir (Abies shastensis) and mountain hemlock (Tsuga mertensiana) forests are on the surrounding drier soils. Historic fires and seasonal ponding may keep the lodgepole pine, mountain hemlock, and Shasta red fir from encroaching onto the Meadow Fen site. Many small trees are on this site. Many older trees, 80 to 100 years old, are in the bog areas, but the trees in the riparian areas are much younger, suggesting an occasional purge of conifers from the wet areas as a result of a relatively hot fire. The frequency of fire is probably similar to that of the surrounding forest sites. Fire suppression efforts since 1900 possibly have decreased the extent of the Meadow Fen site because the canopy cover of woody species has increased and the cover of grasses and sedges has decreased.
The Meadow Fen site provides important cover and food for wildlife. Elk feed extensively in areas of this site in summer. It is the most productive rangeland site in the park. Production of air-dry vegetation is estimated at 7,500 to 9,500 pounds per acre per year.
The Sphagnum Fen ecological site occurs in association with the Meadow Fen site, but the Sphagnum Fen site generally is wetter. Some areas of this site have very deep accumulations of rubbed fibers and mucky peat soils. This site is the most diverse rangeland site in the park. It supports a large number of species, but dominantly water sedge (Carex aquatilis), fewflower spikerush (Eleocharis quinqueflora), pullup muhly (Muhlenbergia filiformis), and tufted hairgrass (Deschampsia caespitosa). The more “boggy” areas of this site support carnivorous sundew (Drosera anglica and D. rotundifolia) and a discontinuous carpet of sphagnum moss.
This site shares a natural dynamic relationship with a slightly higher lying plant community of bog blueberry (Vaccinium uliginosum). This plant community develops in areas where organic matter accumulates into hummocks. These hummocks are slightly higher lying and drier than the surrounding areas; thus, they provide the microenvironment necessary for bog blueberry. Windthrown pine and fir slowly decompose and form the hummocks and the substrate necessary for establishment of the shrubby species. In some areas the hummocks support an almost pure stand of bog blueberry and water sedge. Wildfire probably plays a role in removing the hummocks, which “evens out” the microtopography, and returning the plant community to sedges and grasses.