Environmental Relationships in Forests of Early 20th Century Coos County, Oregon, Based on Timber Cruise Data

Abstract

Timber cruise data can provide useful information not available elsewhere. Measurements of timber volume (timber cruises) from the early 20th century for Coos County, Oregon, were used to assess the degree to which tree species distribution and timber volume varied with edaphic and climatic factors. The study area has diverse geology in a moderate maritime climate, and represents an area of forest transition between the Coast Range and the Klamath Mountains. Species distribution was determined from 629 cruised 1-mi2 (2.59 km2) sections, and timber volume from 252 sections of old-growth forest. Most forests were dominated by Douglas-fir (Pseudotsuga menziesii); Sitka spruce (Picea sitchensis), although least frequent, had the second-most timber volume. All six commercial conifer species differed substantially in distribution in relation to geography and to environment. Both distribution and volume of grand fir (Abies grandis) varied with geologic unit and general soil type: Sitka spruce, with soil and maximal summer temperature (–sign); Douglas-fir, with temperature ( ) and summer precipitation ( ); western hemlock (Tsuga heterophylla), with precipitation ( ); Port-Orford-cedar (Chamaecyparis lawsoniana), with precipitation (–); and western redcedar (Thuja plicata), with no factor. Importance of Douglas-fir and hemlock increased on geologic units with sediments from inland plutonic sources, which reduced importance of Port-Orford-cedar. Some species varied significantly among soil units within a geological formation, and vice-versa. When choosing which species to plant, these cruise data can supplement or replace guidelines based on plant associations.