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Mohawk Research Natural Area

Eugene District , BLM

West Cascades, Oregon Ecoregion

Cell(s):

  • Douglas fir-western hemlock/Oregon grape and salal forests, with grand fir
Mohawk Research Natural Area

Access by gravel surface road

The Mohawk RNA protects 118 ha of old-growth Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) in the Coburg Hills northwest of Eugene, Lane County, Oregon. The RNA has a north to northeast exposure with elevations ranging between 414 and 695 m. Landforms include a slump bench, a steep slope-scarp face, and a relatively broad ridge top. There are several small marshy areas with permanent standing water, the largest of which covers about 1.6 ha. The RNA is drained by a number of intermittent streams which feed into the McGowan Creek drainage. Soils are assigned to four series: Cumley, Honeygrove, Klickitat, and Peavine. These are deep to moderately deep, well drained to moderately well drained soils formed on igneous rocks. The maritime climate is characterized by cool, wet winters and warm, dry summers. Annual precipitation averages 122 cm, most of which falls as rain between November and March. Forests are dominated by Douglas fir, although western hemlock and western red cedar (Thuja plicata) are also abundant. Douglas fir in the stand appears to form three cohorts. The oldest trees, 400-year-old Douglas fir scattered throughout the stand, have open grown characteristics and DBHs of 1.5 m. A second age class, which includes western hemlock and western red cedar, consists of mature second growth established after 1850. Younger trees are pole-sized Douglas fir and hemlock. Hemlock dominates the reproductive stage in the stand with many seedlings and saplings. In addition, the coniferous component of the stand includes grand fir (Abies grandis), incense cedar (Calocedrus decurrens), and Pacific yew (Taxus brevifolia). Deciduous trees include bigleaf maple (Acer macrophyllum), red alder (Alnus rubra) and black cottonwood (Populus trichocarpa). Dwarf Oregon grape (Berberis nervosa) and salal (Gaultheria shallon) are common in the understory. Natural disturbances include fires and windstorms. Fire scars are present on all of the old, open-grown Douglas fir. The 1962 Columbus Day storm left extensive blowdown. Individual trees were salvaged on the benches and a 15 ha area was clearcut, then replanted in 1965. A guidebook written by Allan Curtis is available, Mohawk Research Natural Area Supplement 23, 1986. In 1978 George C. Carroll, University of Oregon, published an article in Canadian Journal of Botany (56): Studies on the incidence of Coniferous Needle Endophytes in the Pacific Northwest. Peter Schoonmaker, Harvard University, studied pollen, macrofossil and charcoal analysis (1989).
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