Graduate Thesis Or Dissertation
 

Forest associations and secondary plant succession in the southern Oregon coastal range

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  • Forest associations, secondary succession, and relationships of plant communities to Roosevelt elk were investigated. Stratification of vegetation into ecological units and an understanding of secondary succession by habitat-type were a necessary first step in investigations into browsing of conifers by elk. The study was jointly conducted by the Oregon State Game Commission and the Weyerhaeuser Company. Vegetation, soils, and physiography were studied together. Vegetation cover data, recorded in thirty-two, 275 to 500-year-old forest stands, formed the basis of a synecological classification. Lightspots are a natural component of these forests. The dense forest and a lightspot were separately sampled in each stand. Light-spot cover data were analyzed separately in an association table. Lightspot data were compared with dense forest data to check validity of the phytosociological classification. This approach increased phytosociological understanding of these forests. The climax dominant tree and shrub and herb layer species with highest cover are used in naming the following associations (in order of increasing xerism): Thuja/Adiantum-Athyrium Tsuga/Polystichum/Oxalis Tsuga/Acer/Berberis Tsuga-Pseudotsuga/Rhododendron/Berberis Pseudotsuga/Holodiscus/Gaultheria. The exceptions are Adiantum pedatum and Athyrium filix-femina, high constancy, low cover, indicator species, used in naming the Thuja/Adiantum-Athyrium association. Polystichum munitum and Oxalis oregana dominate the herb layer of this association. Associations will be referred to in the abstract by a two-part name. The Adiantum-Athyrium association has the following additional indicator species: Blechnum spicant and Marah oreganus. Stands usually occur near the bottoms of lower elevation canyons. The moist, stony, Slickrock soil series underlies most stands. The Polystichum/Oxalis association is the most widespread and variable community studied. Tiarella trifoliata has high indicator value for this association. The presence of any one of Stellaria crispa, Montia sibirica, Dicentra formosa or Athyrium filix-femina in lightspots effectively differentiates stands of this association from related ones of the Acer/Berberis association. Stands frequently occur on lower and middle slopes and are usually underlain by the Matson or Apt soil series. In the Acer/Berberis association, Acer circinatum has high cover only in lightspots. Most stands are found on the Millicoma or Matson soil series. Stands occur on lower and middle slopes. Stands of the Rhododendron/Berberis association usually occur on south-facing, upper slopes and ridgetops where high winds frequently cause blowdown. The resultant large openings allow regeneration of Pseudotsuga menziesii. Rhododendron macrophyllum has low cover in the dense forest but high cover in lightspots. Allotropa virgata, a low constancy (saprophyte), has high fidelity to the association. The Millicoma, Matson or Ivers soil series underlie most stands. The Holodiscus/Gaultheria association has the following high fidelity species: Philadelphus lewisii, Symphoricarpos mollis, Madia gracilis, Hierochloe occidentalis, Ligusticum apiifolium, and Lonicera hispidula. This is the only association studied in which the lightspot phenomenon was not important. With the exception of Pseudotsuga menziesii regeneration, understory vegetation did not increase in cover when the tree canopy was removed. Stands usually occur on south-facing, upper slopes and ridgetops. The Digger or Agony soil series are associated with most stands. The successional influence of soil-surface disturbance caused by logging was studied in 1 to 15-year-old stands of the Polystichum/Oxalis and Rhododendron/Berberis habitat-types. In the Polystichum/Oxalis habitat-type, the vegetative dominants by years since logging are: Senecio sylvaticus--first year; Deschampsia elongata--years 2 to 4; Aira caryophyllea, Rubus ursinus, Hypochaeris radicata and Crepis capillaris share dominance--years 5 to 9; Hypochaeris radicata and Pteridium aquilinum share dominance--years 10 to 15. Pseudotsuga menziesii increased to 16 percent cover in the 10 to 15-year period. Disturbed areas of the Rhododendron/Berberis habitat-type have more than 65 percent bare ground for two years after logging. The vegetation dominants by years are: Deschampsia elongata--years 3 to 4; Hypochaeris radicata and Rubus ursinus--years 5 to 7; and Pseudotsuga menziesii--years 8 to 15. Other high cover species in the 8 to 15-year period are Thermopsis montana, Rubus ursinus, and Pteridium aquilinum. Selected stages in secondary succession were studied from one year after logging to climax in the two most important habitat-types. In the Polystichum/Oxalis habitat-type, Pseudotsuga menziesii is the seral tree dominant but is replaced by Tsuga heterophylla in climax. The tall shrub Acer circinatum has high cover in those serai stages with a comparatively open tree canopy. The herb layer is dominated throughout secondary succession by Polystichum munitum and Oxalis oregana. The tree layer of serai stands of the Rhododendron/Berberis habitat-type is dominated by Pseudotsuga menziesii. Either Tsuga heterophylla or Pseudotsuga menziesii dominate near-climax stands. The shrub layer dominant is Rhododendron macrophyllum throughout secondary succession. It has low cover in the dense forest but high cover in lightspots of near-climax stands. Berberis nervosa has nearly constant coverage throughout secondary succession in the Rhododendron/Berberis habitat-type and is the herb layer dominant in near-climax stands. Herb layer dominants in early serai stages are: Senecio sylvaticus--year 1; Erechtites prenanthoides--year 2; Rubus ursinus and Gaultheria shallon--years 4-15. Classification and recognition of habitat-types are possible throughout secondary succession from logging to climax on the basis of the same indicator species. The dominance level of some species changes with seral stage, but the change is predictable. Preferred elk food is about twice as abundant in the Polystichum/Oxalis as the Rhododendron/Berberis habitat-type. Nutritious, preferred elk food is most available in the 4 to 9-year period of secondary succession. Present logging methods which leave a mosaic of intermingled disturbed and undisturbed areas create a habitat beneficial to elk. The animals forage on disturbed areas for preferred invader species and on adjacent undisturbed areas for forest remnant species.
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