Distribution and abundance of terrestrial and arboreal lichens in the old-growth coniferous forests of the western Cascades of Oregon, with special reference to nitrogen-fixing species

Lichens are a conspicuous component of moist coastalforests west of the crest of the Cascade Mountains fromnorthern California to southern Alaska , a region referred to here as the Pacific Northwest or PNW. Lichens are of interest in this region not only because of their abundance, estimated to be up to one to two metric tons per hectare in mature forests (Edwards et al. 1960; Pike 1971; Pike et al. 1972), but also because several common species fix atmospheric nitrogen (Pike 1973; Pike et al. 1976).
In general, lichens are composed of two organisms-- the mycobiont (a fungus) and the phycobiont (an alca) -- which live together in a symbiotic relationship. Some lichens have three symbionts: fungus; green alga; and blue-green alga. Lichens may be referred to as cyanophiles if they contain a blue-green alga or as non-cyanophiles if they contain only a green alga.
If the phycobiont is a blue-green alga of the genus Nostoc, then the lichen may be assumed to possess the ability to fix atmospheric nitrogen (Millbank and Kershaw 1970). Several lichen species containing blue-green phycobionts other than Nostoc have also been demonstrated to fix nitrogen. The nitrogen is fixed by the primary phycobiont if the Nostococcurs in a continuous layer throughout the lichen thallus(plant body) or by the secondary phycobiont if the Nostoc is concentrated in internal or external cephalodia (nodes).
Since nitrogen is commonly a limiting nutrient inforest communities, management of nitrogen input will be an important tool in forest practices of the future. In addition to, or possibly instead of, applying
industrially-fixed nitrogen, it may be desirable to manage the nitrogen input biologically. Cyanophilous lichens appear to play an important role in the nitrogen cycle at the ecosystem level in the Douglas fir
(Pseudotsuga menziesii (Mirb.) Franco) region (Pike et al. 19727Pike 1978).
An understanding of the abundance and distribution of lichens is essential to determine the role of lichens inany given ecosystem, to gain a perspective on their management potential, and to identify their relationship to vascular plant distributions. Several studies of lichen distribution in the PNW have been published: on the scale of individual trees, lichen distributions have been studied on old--growth Douglas fir in the Andrew's Experimental Forest in the western Cascades of Oregon (Pike et al. 1972, 1975, 1977); on the scale of closely adjacent stands, Pike (1971) studied epiphytic lichens in an oak forest in the Willamette Valley of Oregon and Pechanec and Franklin (1968) conducted a study of the epiphytic lichens in stands of red alder (Alnus rubra Bong.) at Cascade Head on the north-central Oregon coast; and on the scale of stands within a broad region are two studies of epiphytic lichens on the Olympic Peninsula in Washington (Brown et al.1956; Hoffman and Kazmierski 1969) and Szczawinski's (1953) study of lichens living on bark and decaying wood substrates inthe Douglas fir forests of Vancouver Island in Canada. None of these studies have made cross-stand comparisons of total lichen but instead have compared quantities of lichens present on specific portions of host trees (e.g. lower trunk, upper trunk, and branches).
The present distributional study was performed on a scale of forest stands and involves both epiphytic and ground-dwelling lichens. Although age of the stand is clearly an important factor in determining the distribution of lichens, that factor is not considered here and quantitative observations were limited to a set of mature forest stands. This study wasundertaken on the H.J. Andrews Experimental Forest near BlueRiver, Oregon (hereafter referred to as the AEF) as part of a research program attempting to determine the significance of these lichens in the nitrogen cycle of the Douglas fir forests.
The objectives of this study were:
1) to determine what species of cyanophiles occur in AEF
2) to determine the habitat and substrate requirements of these lichens
3) to determine the quantitative distribution of the cyanophiles in the AEF
4) to determine whether lichens are index species to vegetational zones and/or community types
5) to determine which environmental factor(s) are important in the distribution of the lichen flora
6) to determine the biomass and potential for nitrogen fixation by lichens in the AEF
Both cyanophiles and non-cvancmhiles were sampled in this
dy with emohasis on the cyanophiles. The non-cyanophilousspecies were studied in the hope that they would prove useful as predictors of the distributions of cyanophilous species.The sampling was performed in a variety of communities and habitats found within the AEF.
The cyanophilous and non-cyanophilous lichens include both terrestrial and arboreal species. The biomass of terrestrial lichens can be sampled directly, but the complexities
of sampling arboreal species make direct measurements impractical when sampling several stands of trees. Since there is a considerable "rain" of lichen material from the canopy onto theforest floor, the presence of lichens in the canopy can be deduced from an examination of the litter. Furthermore, it is reasonable to assume that even though turnover rates for lichens both in the canopy and in the litter may vary from stand to stand, the abundance of epiphytic litter on the forest floor reflects the abundance of lichens in the canopy.
Although epiphytic lichens have different patterns of dispersion over portions of host trees from one stand to another, sampling of the epiphytic litter gives an integrated picture of biomass and species content of the lichen flora for the whole canopy.
These biomass data for each site were compared and correlated with a wide variety of environmental factors to detect patterns which might help explain the observed lichen distributions. The data gathered in this study were supplemented by environmental data gathered on the AEF by the United States Forest Service and the International Biological Program.This data base provided considerable resources on soils, meteorology, fire history, community types, and the compositionof vascular plant flora.
Analysis of the distributional data suggested that the heavy condensation and reduced evaporation in the valley bottoms creates moister conditions for the canopy lichens thanat. adjacent higher elevations. The relationships of these conditions to lichen distributions were explored by sampling Iichens and measuring candensation drip and evaporation along a transect traversing the Lookout Creek Valley in the AEF.