Mass loss and nitrogen dynamics during the decomposition of a 15N-labeled N2-fixing epiphytic lichen, Lobaria oregana

We studied mass loss and nitrogen dynamics during fall and spring initiated decomposition of an N2-fixing epiphytic lichen, Lobaria oregana (Tuck.) Müll. Arg., using 15N. We developed a method of labeling lichens with 15N for use in a decomposition study that involved spraying lichen material with a nutrient solution containing 15N-enriched ammonium. Through the first 180 days of sampling, lichens placed in the field during the spring had a smaller decay constant (k = 1.24 year–1) than the lichens placed in the field during the fall (k = 3.1 year–1). However, both spring and fall lichen samples were decomposed beyond recognition after 1 year. Patterns in exogenous N uptake and N concentration did not differ by season. Both spring and fall lichens took up N from the surrounding environment during decay while simultaneously losing N to the environment. The N concentration in both sets of lichen additions increased during decay to a peak of around 2.8% N, equal to a C to N ratio of about 16, and then began to decrease. This indicates that early in decay, net N immobilization occurred in the remaining lichen, but this was followed by net N mineralization in later stages of decay.Key words: decomposition, nitrogen, Lobaria oregana, lichen, mineralization, immobilization.

Distribution of epiphytic macrolichens in relation to remnant trees in a multiple-age Douglas-fir forest

Alternatives to clear-cutting are being implemented to increase biodiversity of managed forests in the Pacific Northwest. Lichens are an integral component of old growth, but lichen biomass develops slowly in forests. We evaluated the long-term potential of live tree retention for lichen conservation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. We sampled lichen litterfall in a 2-ha stand that contained 200- to 600-year-old remnant trees scattered in a forest composed mostly of 100-year-old trees that established following fire. We used association, principal components, and regression analyses to relate lichen litterfall biomass to the proximity of remnant trees. Two epiphytic lichens were strongly associated with remnant trees: the foliose cyanolichen Lobaria oregana (Tuck.) Müll. Arg. and the fruticose green algal lichen Sphaerophorus globosus (Hudson) Vainio. Biomass of both species was highest near remnant trees, and biomass was slightly higher within groves of remnant trees than it was at the edges of these groves or near isolated trees. Lichens appear to have persisted on remnant trees through the last fire and are slowly recolonizing younger trees from this source of propagules. Retention of live trees, maintenance of hardwoods, and longer rotation periods have great potential to maintain old-growth-associated lichens in at least some managed forests.

Consumption and Decomposition of Lichen Litter in a Temperate Coniferous Rainforest

Nylon mesh litter–bags markedly reduced the rate of weight loss of lichen litter, as compared to unconfined (free) lichens, suggesting that herbivores and detritivores larger than the mesh size make a significant contribution to the disappearance of lichen litter. The half–life of free lichen litter was 1·5 months for Alectoria sarmentosa, 2·5 months for Hypogymnia inactiva, 3·5 months for Platismatia glauca, and 7 months for Lobaria oregana. The half–lives were 2·9 times longer for the same species in litter–bags. Because A. sarmentosa showed the greatest difference between free litter and litter–bags, we conclude that, of the four species studied, it had the highest rate of consumption by larger herbivores and detritivores.