Ecology of Subalpine Meadows in the Olympic Mountains, Washington

Abstract

The following eight community types in the Olympic Mountains, delimited from an ordination of 38 plots, are described: (1) the cushion plant type occurring in dry habitats on exposed knolls or ridge tops; (2) the dry grass—forb type occurring on steep, dry, south— to west—facing slopes; (3) the mesic grass type occurring on mesic, south— to west—facing slopes; (4) the moist Saussaurea forb type occurring in shallow gullies kept moist by melting snowbanks or shallow streams; (5) the moists Valeriana forb type occuring on steep, northeast—facing slopes; (6) the tall sedge type mostly occurring at higher elevations on many aspects and topographic situations, depending on location in the Olympic Mountains; (7) the heath shrub type occurring in cool habitats where snow remains until mid— to late July; and (8) the dwarf sedge type occurring in high subalpine to alpine areas where snow remains until late July to early August. Soils are mostly poorly developed (Entisol and Inceptisol), but some have well—developed horizons (Spodosol). The less developed soils generally had higher amounts of available nutrients. Physical properties differed little between soils in each community, except for the fraction >2 mm which varied from a high of 82% in the dry grass—forb community to a low of 31% in the tall sedge community. Solar radiation, wind velocity, precipitation, atmospheric moisture, temperature, and soil moisture were monitored in the dry grass—forb, mesic grass, and Saussaurea forb communities. Total solar radiation received was similar in the summers of 1966 and 1967. Wind velocity was low in all communities; the highest average for a summer was 1.2—1.6 m/sec in the mesic grass community. Temperatures and vapor pressure deficits were highest in the dry grass—forb community and lowest in the moist Saussaurea forb community. Precipitation differed little among stations. Soil moisture in 1967 was available for the shortest period in the dry grass—forb community and 3 and 5 weeks longer in the mesic grass and moist Saussaurea forb communities, respectively. Shoot productivity was determined in three communities, and standing crop of shoots and roots was determined in five communities. Productivity values were 1.2, 2.7, and 11.4 g/m2 per day in the dry grass—forb, mesic grass, and moist Saussaurea forb communities, respectively. Peak shoot production, ranked from low to high, was dry grass—forb (107 g/m2), dwarf sedge (157 g/m2), mesic grass (245 g/m2), tall sedge (395 g/m2), and moist Saussaurea forb (502 g/m2). Peak root production ranged from a high of 3,257 g/m2 in the tall sedge community to a low of 1,234 g/m2 in the moist Saussaurea forb community. Chlorophyll content in the five communities followed the same trend as shoot production. The correlation between ovendry weight of shoots and chlorophyll content was high (r = .70, p < .01). Differences in water potentials were small among the species from the dry grass—forb, mesic grass, and moist Saussaurea forb communities, and the lowest water potentials were mostly between —14 and —16 bars. The effect of light, temperature, and soil moisture on photosynthesis was determined for Caltha leptosepala (wet site species), Saussaurea americana (moist site species), Festuca idahoensis and Lupinus latifolius (mesic site species), and Eriophyllum lanatum (dry site species). Except for the temperature response of Caltha and Eriophyllum, response of the five species to the three environmental factors helped to explain their natural distribution.