Canopy Lichens with Blue-Green Algae: A Nitrogen Source in a Colombian Rain Forest

Lichens containing blue—green algae are abundant (13,600/ha; total biomass 5.7 kg/ha) in a Colombian montane rain forest. These noncrustose lichens grow mainly on 3—12 cm diam twigs and small branches, 12—25 m high at the top of the crowns of canopy and subcanopy trees. They are rare below 4 m. Eighty—six % of the lichens contain Nostoc and, based on published laboratory nitrogen—fixation studies of lichenized Nostoc, these lichens fix an estimated 1.5—8 kg N/ha°yr, equivalent to the estimated range of total nitrogen input in precipitation. This lichen phenomenon is probably widespread in rain forests of the American tropics. These results reemphasize the importance of the epiphyte community in the canopy layer of the rain forest ecosystem.