The Importance of Epiphytic Lichens in Mineral Cycling

Mineral capital in epiphytic lichens varies considerably from forest to forest depending primarily on the biomass of lichens present and can be at least as high as 27 kg ha-1 for N, 3.6 kg ha-' for P, 9 kg ha -' for K, 9.4 kg ha-1 for Ca and 1.7 kg ha-1 for Mg. For three ecosystems, comparing Douglas fir, balsam fir and oak woodland, lichens seldom accounted for more than 10% of the annual, above-ground turnover of a mineral. Lichens were relatively more important in the cycling of N than of P and K and of least importance in the cycling of Ca and Mg. Quantities of minerals leached from lichens appear to be small compared to quantities released through bio- mass turnover. Lichens may influence entry of minerals into ecosystems through nitrogen fixation and interception of aerosols. Although atmospheric inputs may be sufficient to meet N, Ca and Mg requirements of epiphytic lichens, P and K appear to be obtained primarily as leachates from other canopy components. Minerals that have been taken up by lichens may sub- sequently reach the surrounding plant or animal communities via litterfall, leaching, bacterial incorporation or non-cellular particle formation.