Structure and composition of old-growth and unmanaged second-growth riparian forests at Redwood National Park, USA

Author

Emily Teraoka

Graduation Date

2010

Document Type

Thesis

Program

Other

Program

Thesis (M.A.)--Humboldt State University, Natural Resources: Forestry, 2010

Committee Chair Name

Christopher Keyes

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Humboldt State University -- Theses -- Forestry, Riparian forest, Structure and composition, Old-growth forests, Redwood National Park, Second-growth forests

Abstract

Restoration of riparian forests that have been harvested in the past has become an important issue for managers of redwood (Sequoia sempervirens [D. Don] Endl.) forest reserves. Old-growth riparian forests can be used as a reference to direct restoration efforts, but in the redwood region they have lacked detailed study. Riparian forests in adjacent watersheds at Redwood National Park were studied to understand the structure and compositional differences between old-growth and unmanaged second-growth forests. In the old-growth, redwood was the dominant species in the overstory in terms of basal area, height, stem density, and importance values. Second-growth was dominated by red alder (Alnus rubra Bong.), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), and redwood. Polystichum munitum (Kaulf.) C. Presl, Blechnum spicant (L.) Sm., and Athyrium filix-femina (L.) Roth dominated the understory in both old-growth and second-growth riparian forests. Understory species were similar in both forests, although Oxalis oregana Nutt. and Trillium ovatum Pursh had greater importance values in the old-growth whereas Vaccinium parvifolium Sm., Dryopteris sp and sedges Carex spp. had greater importance values in the second-growth. A growth model was used to project 50 years of growth in the second-growth riparian forest for three different scenarios: the current stand without any manipulation; the current stand without red alder (to evaluate the role of red alder on riparian forest development); and the current stand following a thinning prescription designed to reduce basal area of the stand by 25% targeting removal of dominant and co-dominant Douglas-fir. Growth projections of scenarios with red alder resulted in declines in red alder importance after 50 years. All growth projections resulted in redwood increasing importance to a dominant or co-dominant role in the stand with Douglas-fir. However, Douglas-fir maintained a higher position in the canopy than redwood across all scenarios with much higher densities than in the old-growth. Results suggest that if the desired future condition of the second-growth riparian forest is redwood-dominated (comparable to that found in old-growth), intervention will be necessary to reduce the dominance of Douglas-fir, especially dominant, upper canopy Douglas-fir, while maintaining redwood both in the upper and lower canopy.

https://scholarworks.calstate.edu/concern/theses/9s161856h

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