Using rope techniques for access, we surveyed epiphytes on five Sitka spruce trees up to 92 m tall in an old-growth redwood forest. We quantified epiphyte diversity by sampling 5% of each tree's surface area of axes (branches >5 cm diameter) and branchlets (branches <5 cm diameter, including foliage). Epiphyte communities included 57 macrolichen, 15 crustose lichen, 17 bryophyte, and two fern species. The five most abundant species—Isothecium myosuroides, Polypodium scouleri, Polypodium glycyrrhiza, Lobaria pulmonaria, and Frullania nisquallensis—contributed 42.1, 13.3, 8.4, 6.7, and 4.7% of the total epiphyte biomass, respectively. There was an average of 36.2 kg of bryophytes, 9.9 kg of lichens, 12.7 kg of ferns, and 131 kg of associated dead organic matter per tree. Axes supported 83% of the biomass and 98% of the dead organic matter. At the whole-tree level, bryophyte biomass was 11.3 times higher and lichen biomass was 2.5 times lower on axes than branchlets. Ferns were restricted to axes. Ordination analysis revealed one dominant gradient in epiphyte composition that was positively correlated with height and lichen diversity, and negatively correlated with bryophyte diversity. Chlorolichens dominated the exposed portion of the gradient with equivalent amounts of cyanolichens and bryophytes. Mosses dominated the intermediate portion of the gradient with equivalent amounts of liverworts, cyanolichens, and chlorolichens. There was very little lichen cover in the sheltered portion of the gradient, which was dominated by bryophytes. Extensive bryophyte mats with large quantities of dead organic matter promote biological diversity on Sitka spruce in redwood forest canopies by storing water and serving as habitats for desiccation-sensitive organisms.
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Vol. 106 • No. 2