Document: EST-3-76-10

Growth and production of dominant riparian trees in the Pacific Northwest coastal rainforest.

BALIAN, E.V.* and R.J.NAIMAN

University of Washington, Seattle, WA 98195, USA. ¹

Abstract:
Few published studies focus on productivity and growth processes of riparian forests in the Pacific Northwest, despite the importance of riparian forests in stream structure and function. The objectives of this study are to identify growth patterns for dominant riparian tree species and production processes of riparian forests related to geomorphic and successional characteristics. The research area is located in the low valley of the Queets River, on the western coast of Washington's Olympic Peninsula. The dominant riparian species in the Queets river valley are red alder (Alnus rubra) and willow (Salix sp.) in the younger stands, and Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) in the mature stands. Cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and bigleaf maple (Acer macrophyllum) appear as intermediate species in older stands. Sixteen plots have been established on three different templates: active floodplain (< 20 years), paleo-floodplain (30 to 70 years) and low terrace (80 to > 500 years). Basal area and density are annually recorded for each plot. Early successional plots colonized by young alder and willow (< 20 years) show the highest density (22000 to 35000 trees/ha) and the lowest basal area (7.4 to 18 m²/ha), while mature stands (400 to > 500 years) are characterized by low density (248 to 588 trees/ha) and high basal area (64 to 97 m²/ha). A total of 564 trees are being surveyed for growth between April and October (growing season), by using dendrometers (50 trees) and sequential measurements. The first results for 1999 show that western hemlock has the greatest average basal area increment per tree (>100 cm²/growing season), while red alder in younger plots exhibits the highest total basal area increment per surface unit (1.09 to 2.1 m²/ha/growing season). Cottonwood's basal area increment tends to occur later in the Fall, following the first important precipitation. Results on growth processes are being used to develop a semi-quantitative model describing production process changes taking place over time. This model will give an estimation of the time riparian species require to begin supplying the aquatic system with woody debris.

Keywords: Riparian vegetation, growth, production, rainforest

This abstract is being presented at: 11:15 AM in session:
Oral Session #20: Riparian Ecology.