Lichens were studied in forested stands originating after stand-replacing fires 510, 140, 70 years ago (Teensma 1987) or after clearcuts 40 years ago. Howe (1978) found that northern aspects in old growth reference stands at the H.J.Andrews had greater lichen biomass than southern exposures, and that cyanolichen abundance was greatly limited beyond 150 m vertical distance above streams. In this study I sought to observe how the lichens of different forest age classes compared under optimal conditions and, therefore, chose northern aspects within riparian environments. I hypothesized that suboptimal conditions might mask differences in abundance and biomass among the younger age classes. To focus primary attention on differences among age classes, I tried to maintain as many other environmental variables as possible constant.
Three study stands were chosen to represent each age class. Stands were chosen according to the following criteria:
Biomass. Ten 2 m radius circular plots were chosen at random within each site. All lichen litterfall within each plot was gathered according to the protocol of McCune (1993a): Lichens were cleaned of debris, and sorted into bags according to three functional groups-- "cyanolichens","Alectoriod" lichens, and "other" lichens. "Cyanolichens" were defined as those macrolichens employing cyanobacteria as primary or secondary photobionts (mainly Lobaria, Nephroma, Pseudocyphellaria, Sticta, and Peltigera in the western Cascades.) "Alectoriod" lichens were defined as pendulous or tufted fruticose lichens in the genera Alectoria, Bryoria, and Usnea. "Other" lichens included all remaining lichens.
Lichenologists have been traditionally limited in their ability to undertake large scale ecological studies by the time required to rig and sample individual trees. In attempting to design a method to quantify standing lichen biomass without having to climb (and pillage the epophytes of) hundreds of trees, McCune (1993a) studied the relationship between lichen litterfall and standing crop. His litterfall pickup methodology was designed to capture the steady rain of lichens falling freely from the canopy or attached to small branches. He reports that the correlation between litterfall and standing biomass was highest (r2=0.87) when he discounted decomposing lichens and large, anomalous clusters of lichens attached to large limbs. As the latter occur only rarely in litterfall plots, he reasoned, collecting such clusters would have generated unnecessary statistical noise.
Employing McMune's guidelines, lichens were left uncollected if:
Species capture . Direct observation of the canopy by climbing suggested that biomass sampling plots detected the lichen species that constituted the vast majority of lichen biomass in the forest, but did not adequately detect rare lichens. In characterizing the species composition of stands for forest health/air quality monitoring, McCune and Dey (1992) found that most lichen species in a stand may be found within a 36.56 m (120 ft) radius sample plot (0.42 ha). Adapting this methodology, lichen species not already encountered in the biomass sample plots were collected from within a circle of 11.56 m radius around plot center. The ten combined species plots were equal in area to one 36.56 m circle.
Species collection were limited to epiphytic macrolichens. Terrestrial lichens, though important in the ecosystem, were avoided for two reasons. First, McCune's litterfall ratio did not adequately quantify their biomass or their biomass importance relative to other lichens; and second, neither litterfall plots nor species capture plots adequately sampled them, as they often grow on patchily distributed mineral soil, rocks, or coarse woody debris. Crustose lichens were avoided for the same reasons. Epiphytic macrolichens were defined as those growing higher than 2 m above the ground in order to exclude species found equally on tree bases and coarse woody debris or soil (e.g., Cladonia spp. and Peltigera spp.)
Lab Analysis. Lichens were oven dried at 60 degrees C for 24 hr according to the methodology of McCune (1993a). Functional group bags from each plot were then weighed to the nearest 0.01 g. Species biomass was assessed visually as a percent of the functional group biomass in each bag. Lichens were identified to the most specific taxonomic level possible using Goward et al. (1992), Brodo and Hawksworth (1977), Hale (1979) and herbarium specimens at Oregon State University (OSC). Nomenclature follows Egan (1987).
Identifications were verified by Dr. Bruce McCune.
