Vertical distribution, nitrogen content, and natural 15n and 13c abundance of epiphytic macrolichen functional groups and soil in sub-boreal spruce forests of central British Columbia.

Forest canopy research in old growth sub-boreal spruce (SBS) forests of British Columbia's (BC) central interior plateau forests has revealed rich epiphytic lichen communities that represent a critical interface between the atmosphere and the soil. Cyanolichens can contribute nitrogen (N) to forests by fixing atmospheric N₂ gas into available, reduced forms such as ammonium (NH₄⁺). Variations in the ratios of the natural abundance of the stable isotopes of N (i.e. ¹⁴N:¹⁵N) in forest ecosystem components represent an important in situ method to estimate N inputs from biological N₂-fixation. I used this method to evaluate the importance of epiphytic cyanolichens to N inputs in sub-boreal forest ecosystems of central interior BC. Four old growth sub-boreal forest sites were chosen based on cyanolichen abundance and diversity – two High Cyano sites and two Low Cyano sites. Interior hybrid spruce (Picea glauca x engelmannii) and subalpine fir (Abies lasiocarpa) trees were randomly selected at the High and Low Cyano sites and access into canopies achieved through a single-rope technique. Vertical distributions of lichen biomasses were quantified and a vertical niche of foliose chlorolichens was observed in the canopy where cyanolichens were deficient. Lichen functional groups, conifer needle, and soil samples were obtained and their ¹⁵N:¹⁴N, %N, ¹³C:¹²C, %C contents measured using a continuous flow gas isotope ratio mass spectrometer. Comparisons of stable isotope ratios between High and Low Cyano sites were made. Sub-boreal forest epiphytes and foliage had isotopically lighter N (i.e. more ¹⁴N) at sites with high cyanolichen abundance, indicative of greater inputs of biologically fixed-N.