Biomass and distribution patterns of conifer twig microepiphytes in a Douglas fir forest

Abstract

Total cell volume estimates and species composition for twig microepiphytes are presented for four species of coniferous trees common in the Pacific Northwest. Fungal cell volumes per square centimetre were much greater on Pseudotsuga menziesii than on the other conifers sampled; population densities of algal cells were similar on all hosts. On P. menziesii, microbial populations build up as the twigs age, with total cell volumes at a maximum on 6- and 7-year-old twigs; thereafter total cell volumes decline as twig surface areas decline, although population densities remain high. When fungal cell volumes are expanded to tree and stand levels, estimates of 372 cm3/tree and 15 kg/ha are generated. These values are significant in comparison with estimated standing crops of epiphytic fungi on needles (30 kg/ha) and suggest that twig microepiphytes must be considered in any investigation on the role of epiphytes in nutrient cycling in coniferous forests.