Branch Epiphyte Assemblages in the Forest Interior and on the Clearcut Edge of a 700-Year-Old Douglas Fir Canopy in Western Oregon

A total of 65 epiphyte species (macrolichens, bryophytes, and a fern) were found on the branches offour 700-year-old Douglasfir trees, two growing in theforest interior and two growing on the edge of a 20-year-old clearcut. The moss Antitrichia curtipendula and the cyanolichen Lobaria oregana dominated the epiphyte assemblages. Branch epiphyte assemblages were similar to those reported for a 450-year-old Douglas fir forest, but A. curtipendula and Pseudocyphellaria rainierensis were much more abundant in the older forest. Epiphyte species tended to be positively associated with other members of their functional group. Alectorioid and "other" lichens tended to be negatively associated with bryophytes. Several species were closely associated with moss mats. Ordination revealed one dominant gradient in epiphyte composition that was correlated with height. The gradient could be partitioned into an exposed portion with high lichen cover and low bryophyte cover, an intermediate portion, and a sheltered portion dominated by bryophytes. Biomass and species richness of macrolichen litterfall did not differ between the forest interior and clearcut edge, but there were some differences in the vertical distributions of epiphytes. The exposed and intermediate portions of the compositional gradient extended farther down in the crowns of the edge trees. After two decades of exposure on a clearcut edge, moss mats and associated species were still widely distributed within the edge tree crowns. A considerable amount of canopy epiphyte research has occurred in old-growth Douglas fir forests since the pioneering work of Denison (1973), including an extensive floristic survey of canopy epiphytes (Pike et al. 1975), a detailed examination of the components of individual tree crowns (Pike et al. 1977), an analysis of the distribution of epiphytes within a watershed (Howe 1978), an experiment on cyanolichen growth rates in the canopy (Sillett 1994), and comparisons between old-growth and younger forests (McCune 1993a; Neitlich 1993). These last two studies demonstrated that both biomass and diversity of canopy epiphytes, especially cyanolichens and bryophytes, increase with increasing stand age. McCune (1993a) noticed that Douglas fir canopy epiphytes could be classified into functional groups based on both their ecological roles and their patterns of vertical distribution during forest succession. Bryophytes and cyanolichens, or nitrogen-fixing lichens, were only prevalent in oldgrowth forests, where they occupied the lower and middle portions of tree crowns, respectively. Alectorioid lichens, or forage lichens, and other nonnitrogen fixing lichens (hereafter "other" lichens) were prevalent in younger forests as well as oldg owth forests, where they occupied the upper portion of tree crowns. The old-growth forests studied by Denison, Pike, McCune, and Neitlich were all between 400 and 500 years old and located within the H. J. Andrews Experimental Forest. Aside from Sillett (1994), there are few if any, published studies of canopy epiphytes from old-growth Douglas fir forests located outside of this single watershed in western Oregon. In the Pacific Northwest, management for timber production has converted large areas of old-growth 0007-2745/95/301-312$1.35/0 This content downloaded from 157.55. 39.144 on Wed, 21 Sep 2016 05:38:03 UTC All use subject to http://about.jstor. org/terms 302 THE BRYOLOGIST [VOL. 98 TABLE 1. Descriptions of four approximately 700-year-old Douglas fir trees selected for epiphyte sampling in western Oregon. The dagger (t) indicates that tree 3 had recently lost at least 10 m of its top. Both the average and maximum diameters of the 0.5 m axis segments sampled in each tree are listed. Total sampling length is the estimated length of all living branch axes with diameters greater than 7 cm. All measurements are in m. Trunk Number Average Maximum Total Area of Total diameter of living axis axis sampling Sampling Tree forest height at 1.5 m branches diameter diameter length intensity 1 interior 66 2.1 106 0.12 0.29 103 0.243 2 interior 68 2.8 70 0.20 0.37 120 0.108 3 edge 55t 2.4 69 0.11 0.20 165 0.152 4 edge 66 2.0 106 0.10 0.19 93 0.118 forest into a mosaic of remnant forest patches surrounded by clearcuts and regenerating vegetation. The area of interior forest has been dramatically reduced while edge habitats have been proliferated (Spies et al. 1994). Edges of old-growth forests bordering clearcuts are characterized by drier microclimates and higher rates of large tree mortality compared to the forest interior (Chen et al. 1992, 1993). Very little is known about the impacts of these changes on epiphytes, although several endemic epiphyte species appear to be closely associated with old-growth Douglas fir forests (USDA 1994; Neitlich 1993). This study is the first to investigate canopy epiphytes in a Douglas fir forest well over 500 years old. Branches were sampled in large trees growing in the forest interior and on the edge of a clearcut. Epiphyte litterfall was also sampled in these two areas of the forest. There were four principle objectives: 1) analysis of within-tree structure of branch epiphyte assemblages, 2) elucidation of major compositional gradients in epiphyte assemblages, 3) floristic comparison of epiphytes between 700-yearold and 450-year-old Douglas fir canopies, and 4) a comparison between epiphytes of a forest interior and a clearcut edge.