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UBC Theses and Dissertations

Phytocoenoses in the dry subzone of the interior western hemlock zone of British Columbia Bell, Marcus Arthur Money


Five plant associations and one Alluvial Complex are recognized for the Dry Subzone of the Interior Western Hemlock Zone of British Columbia. These include 22 phytocoenoses, here described as biogeocoenoses or forest types. Additionally 3 intrazonal Pinus ponderosa plant associations and 2 interzonal ecotones are discussed. In phytosociological analysis modified Zurich-Montpellier techniques are employed. For tree studies, dominance/ frequency/density (DFD) indices and standard forestry methods are applied. Phytocoenose descriptions are based on synthesis tables which include plant lists (total 538 species), habitat descriptions and tree growth data from 15.5 one-fifth acre plots. Forest types comprise: 1) Lichen association (Cladonietum) - open stands with Pseudotsuga menziesii as the edaphic climax dominant, occurring on xeric rock outcrops; 2) Moss association (Pachistimeto-Callier gonelletum) - closed stands with Tsuga heterophylla as the climatic climax dominant, occuring on me sic sites; this includes 6 forest types; 3) Aralia Oakfern association (Aralieto-Gymnocarpietum) - closed stands with Tsuga heterophylla, Thuja plicata as the edaphic climax codominants, occuring on moist sites; this includes 7 forest types; 4) Devil's Club association (Oplopanacetum) - closed stands with Thuja plicata as the edaphic climax dominant, occurring on wet sites; this includes 4 forest types; 5) Skunk Cabbage association (Lysichitetum) - open stands with Thuja plicata as the edaphic climax dominant, occurring on water-saturated ground; this includes 2 forest types; 6) Alluvial Complex - unstable riverside vegetation dominated by Populus trichocarpa. The Lichen, Skunk Cabbage and Alluvial Complex communities are floristically the most clearly defined, and are readily recognizable on the basis of lesser vegetation dominants alone. Recognition of mesic communities relies on a characteristic combination of species. The zonal (climatic climax) biogeocoenose is the Slope Normal Moss forest type of the Moss Association. The dynamic relationships of forest types are discussed. Secondary succession may go from the deforested stage directly to the climax, if edaphotope disturbance is minimal, but normally a pioneer-tree stage intervenes. This Subzone is unique in that, the pioneer stage of the zonal community may differ substantially from the climatic climax if humus is removed by fire. On mesic sites, proceeding from pioneer-conifer to climax stages, crown cover decreases and lesser vegetation increases. Tsuga heterophylla is the exclusive dominant of the climax forest„ In decreasing order of importance, as determined by DFD indices, Subzone trees are Tsuga heterophylla, Thuja plicata. Pinus monticola, Pseudotsuga menziesii, Betula papyrifera, Picea engelmannii, Larix occidentalis, Populus tremuloides, Pinus contorta, Populus trichocarpa. Abies lasiocarpa and Abies grandis. Most rapid tree height growth of Thuja plicata, Pseudotsuga menziesii, Pinus monticola and Picea engel-mannii occurs in Devil's Club communities; of Tsuga heterophylla, Larix occidentalis, Pinus contorta, Betula papyrifera, Populus tremuloides in Aralia Oakfern communities; and of Populus trichocarpa in Alluvial Complexes. Forest types are more productive in pioneer than in climax stages. Estimates of net primary productivity and standing crop of forest types for tree trunks of all tree species summed as one, showed that the greatest pioneer- conifer stand productivity (1251 kilogram/ hectare/year) and climax stand standing crop (180 x 10³ kg/ha) belong to the Devil's Club association, and the least productive (126 kg/ha/yr) and lowest standing crop (15 x 10³ kg/ha) to the Lichen association. It is concluded that biogeocoenotic classification provides a sound basis for land use planning in this region, and should be applicable to other areas.

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