. Vegetation of Oregon and Washington. Botany Oregon Ecology; Botany Washington (State) Ecology. Figure 147. — Changes in the subalpine forest-meadow ecotones have typically been gradual; however, massive invasions of meadow areas by tree species have taken place in the last 50 years all over the Cas- cade and Olympic Mountains (Paradise Valley, Mount Rainier National Park). toward a modal mesic type. Such changes may be extremely slow, however. Generally, the heather (Phyllodoce-Cassiope) and Vac- cinium deliciosum communities are consid- ered the higher levels of meadow successional series.
. Vegetation of Oregon and Washington. Botany Oregon Ecology; Botany Washington (State) Ecology. Figure 147. — Changes in the subalpine forest-meadow ecotones have typically been gradual; however, massive invasions of meadow areas by tree species have taken place in the last 50 years all over the Cas- cade and Olympic Mountains (Paradise Valley, Mount Rainier National Park). toward a modal mesic type. Such changes may be extremely slow, however. Generally, the heather (Phyllodoce-Cassiope) and Vac- cinium deliciosum communities are consid- ered the higher levels of meadow successional series. Changes in the forest-meadow ecotone have undoubtedly been of greatest interest. Gradual expansion of tree groups appears to have been taking place for many years be- tween the forest and scrub lines except where fires produced temporary setbacks (Swedberg 1961; Franklin and Mitchell 1967). In the last half century, however, massive invasion of meadow areas has taken place at many loca- tions in the Northwest (fig. 147) (Brink 1959; VanVechten 1960; Fonda 1967; Franklin 1966). These invasions are probably related to a short-term climatic fluctuation. Changes in the overall elevation of forest line or scrub line have not been reported in this region with one exception — on Mount St. Helens. Mount St. Helens is a relatively. Figure 148. — Timberline is low (1,340 m.) but advancing on Mount St. Helens, a Cascade Range volcano of very recent origin (less than 2,000 years old). 172. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Franklin, Jerry F. cn; Dyrness, C. T. Portland, Or. : Pacific Northwest Forest and Range Experiment Station, U. S. Dept. of Agriculture
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