Six epiphyte zones are described: base, moist side of trunk, dry side of trunk, upper trunk, axes of branch systems and branchlets of branch systems. The flora of each zone is compared with that of the rest of the tree and with that found on understory vegetation. Epiphyte distribution is related to differences in bark and exposure of major subdivisions of the trunk and canopy.
During the initial ascent of the trunk the diameter and inclination of the trunk were measured at 5 m intervals and the location of each branch system was recorded. Rectangular quadrats, 10 x 25 cm, placed at height intervals of 5 m and at locations 45 degrees and 135 degrees around the trunk on either side of the climbing path, were used in estimating epiphyte cover on the trunk. All of the epiphytes, except crustose lichens, were harvested from a subset of these quadrats, then sorted and weighed.
Biomass of epiphytes on branch systems was initially estimated from information gathered by the climbers, relating to surface area (diameter, length of axes, branch system area, etc.) and cover of epiphytes on each branch system (Denison et al., 1972; Pike et al., 1972). A detailed examination of 5 or 6 branch systems chosen by an unequal probability sampling scheme (Hartley, 1966), favoring sampling branch systems with abundant epiphytes and resulting in a sample distributed vertically through the canopy, enabled us to correct these initial estimates. Both living and dead branch systems were eligible for sampling. Within each sample branch system the axes were divided into 0.5 m lengths out to the furthest point where they were still 4 cm in diameter. One cylindrat (a sampling unit including the cylindrical surface of a 1 dm long axis section) was sampled within each 0.5 m length. Thus the surface area included in a cylindrat varied depending on the diameter of the axis. For each cylindrat the noncrustose species were removed, sorted and weighed. Branchlets were described (e.g., diameter measured and total area and epiphyte cover estimated); one-fifth of them were taken to the laboratory where epiphytes were removed and subsamples were examined for microephiphytes.
Eleven large trees ranging in height from 25-80 m and nine smaller, understory trees were climbed. During the summer of 1970 we sampled the trunk epiphytes of two large Douglas-firs. In 1971 three more were climbed and one was examined by the procedure outlined above. In 1972 six large trees, four Pseudotsuga menziesii, one Tsuga heterophylla (Raf.) Sarg. (western hemlock), and one Pinus lambertiana Dougl. (sugar pine), were studied. The nine understory trees, Tsuga heterophylla, Taxus brevifolia Nutt. (western yew) and Acer circinatum Pursh (vine maple), were sampled in 1971 and 1972; each was treated as if it were a large branch system.
Data used to determine the distribution of epiphytes within the forest came from examination of samples taken during systematic sampling as described above and from additional collections and observations made while climbing the trees for this study, as well as other studies. Voucher specimens of epiphyte taxa are deposited in the herbarium at Oregon State University (OSU).