Forest and Adjacent Burn in the Tillamook Burn Area of Northwestern Oregon

Abstract

The approximately 300,000 acre Tillamook Burn in the northern Oregon Coast Range has been the scene of three major fires. The area burned first in 1933, in a holocaustic fire that covered 244,706 acres and destroyed approximately ten billion board feet of timber (Morris, 1936). Most of the area burned again in 1939, and again in 1945. The later fires killed many patches of forest missed or subject to ground fires only in the preceding fires, and increased the total acreage by extending the boundaries at various places. Descriptions and statistics of the 1933 fire include those by Morris (1936), Isaac (1936), McArdle (1933), Cronemiller (1933) and others. The fires were exceedingly severe and entirely destroyed the forest vegetation over most of the area, with one major exception. One block of unburned timber, approximately 25,000 acres in size, remained in the center of the Burn area following the 1933 fire. The two subsequent major fires reduced this so-called green island to approximately 2,500 acres, the major reduction occurring in 1939. While there were some ground and spot fires in the edges of this remaining stand of forest, the bulk of it was free of any fire damage. This forest is now being logged. Quantitative studies of forest communities in Oregon as a whole are rare and none exist in the literature for the northern half of the Oregon Coast Range. The only records of the pre-Burn forest in this part of the Coast Range were early timber cruises. The study reported here was carried out in the summers of 1955 and 1956 to obtain information on various habitats and environmental conditions within this remaining forest and on the relative importance of its component species. For purposes of comparison, similar data were taken in adjacent areas in the Burn which had been burned only in 1945. The author wishes to thank the Stimson Lumber Company for allowing this work to be done on their holdings, and the State Forester's Office in Salem, Oregon for generous assistance in providing maps and aerial photographs, and information about the Tillamook fires. DESCRIPTION AND HISTORY OF AREA The topography in the part of the Oregon Coast Range occupied by the main Burn is rugged, consisting of narrow ridges and steep-walled valleys. The topography is highly dissected by streams which have eroded down through soft Cenozoic sandstones and around intrusive lava masses which form the skeletons of the sharp ridges. Slopes of 30? to 50? are common and the more or less level areas of the ridge tops are frequently less than '4 mile in width. General elevations of the higher points range from 2800 to 3500 feet above sea level, while the main valleys of two major streams of the area lie approximately 600-1000 feet above sea level. The area of this study lies in the southwest portion of Township 1 North, Range 6 West and in the extreme northwest portion of Township 1 South, Range 6 West, Willamette Meridian. It lies along a major ridge running south-southwest, north-northeast between the heads of two major streams, as shown in Figure 1. The ridge crest varies in elevation from 2900 to 3500 feet above sea level. Several prominent secondary ridges protrude toward the northwest and southeast at more or less right angles to the line of the main ridge. Figure 2 shows the northwest slope of the area analyzed, the general appearance of this portion of the Burn, and the relative locations of the forest and burn areas studied. The coniferous forest of the Oregon Coast Range is included in the Cedar-Hemlock association of the Coast Forest Formation by Weaver and Clements (1938), in the Pacific Douglas fir of the Cedar-Hemlock Forest by Shantz and Zon (1924), and in the Pacific Coastal Forest Formation by Boosting (1956). Over most of its area it is characterized by tall, often luxuriant forests containing such species as Douglas fir (Pseudotsuga taxifolia), western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata) and various true firs (Abies spp.), with Sitka spruce (Picea sitchensis) occurring on lower slopes near the Pacific Ocean. In Oregon, this forest occurs over much of the Coast Range and the western slopes of the middle and northern Cascade Mountains. The behavior of these forest species in succession has been studied by various workers. Prob1 This work was largely supported by National Science Foundation Grant No. G-1702.