baumzaehlen - Primeval Forests & Their Trees

Olympic National Park (3733 km ² ) is famous for its untouched temperate rainforests and snow capped mountains. Elevations range from 0 to 2432 m. The park consists of two separate parts: a narrow strip along the Pacific coast and a large mountainous area to the east of it. Some of the largest known specimens of numerous tree species have been found in the park: Thuja plicata (western redcedar), Pseudotsuga menziesii var. menziesii (coast Douglas-fir), Picea sitchensis (Sitka spruce), Cupressus nootkatensis (Nootka cypress), Tsuga heterophylla (western hemlock), Abies grandis (grand fir), Abies amabilis (Pacific silver fir) and Picea engelmannii (Engelmann spruce) ¹ .

The forests of western North America are unique among the mesic temperate zone regions of the world in that they are almost totally conifer dominated from sea level upwards. This has often been explained by the present climate, with very mild winters and relatively dry summers, both of these phenomena favouring evergreen conifers over summer green angiosperms. Conifers are able to assimilate more effectively during moisture stress (summer) than angiosperms and they are able to continue assimilation almost throughout the mild winter. It has to be noted, however, that on the western slopes of the Olympic Mountains, not even summers are actually dry although most precipitation occurs during autumn, winter and spring: in the western valleys, approx. 250 mm of rain falls in the summer months (June-August). There are also persistent fogs during summer, further increasing the “precipitation”. ² Annual figures right on the coast are approx. 2300 mm, in the western valleys 3000–3600 mm ³ and along the western flanks of Mt. Olympus up to 6000 mm ⁴ . Average annual temperature at the coast is approx. 10°C.

There are about 25 tree species in the park ⁵ , most are easy to identify. On the coastal plain, the most common tree species are Tsuga heterophylla and Thuja plicata . Immediately behind the beaches, particularly P. sitchensis and Alnus rubra (red alder) occur. In the western valleys further from the coast, P. sitchensis and T. heterophylla dominate both in denser forest as well as in those areas with very open canopy, where there is an undergrowth of impenetrable Acer circinatum (vine maple) thicket a few metres tall. In these areas, conifer reproduction is essentially confined to "nurse logs", and it has been suggested that the open forests are the result of insufficient numbers of nurse logs ⁶ . A. rubra groves are common along rivers. The slopes are dominated by Tsuga heterophylla and Abies amabilis on the western side and by Tsuga heterophylla and Pseudotsuga menziesii on the drier eastern side where fire is an important disturbance agent. Tsuga mertensiana (mountain hemlock) is common near the treeline.

In addition to the A. circinatum and Vaccinium thickets, fallen giant trees and many steep slopes make off-trail hiking slow. Camping is allowed throughout the park excepting some areas with high visitation.

References:

1 Van Pelt, R. (2001): Forest Giants of the Pacific Coast. Global Forest Society.

2 Franklin, J. F. & Dyrness, C. T. (1988): Natural Vegetation of Oregon and Washington. Oregon State University Press.

3 Kirk, R. (2001): The Olympic Rain Forest, an Ecological Web. University of Washington Press.

4 Van Pelt, R. (2007): Identifying Mature and Old Forests in Western Washington . Washington State Department of Natural Resources.

5 Latham, R. E. & Ricklefs, R. E. (1993): Global patterns of tree species richness in moist forests: energy-diversity theory does not account for variation in species richness . Oikos 67 : 325-33.

6 Franklin . J. F. & Hemstrom, M. A. (1981): Aspects of Succession in the Coniferous Forests of the Pacific Northwest. In West, D. C., Shugart, H. H. & Botkin D. B. (eds.): Forest Succession. Concepts and Application . Springer.

Official site:

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