BC’s Inland Rainforest – Conservation and Community
The role of overstory tree species in providing habitat for epiphytic cyanolichens
J. Campbell 1, G.E. Bradfield 2, C.E. Prescott 3, and A.L. Fredeen 4
Epiphytic cyanolichens are an important component of canopy systems in the British Columbian Inland Rainforest. Cyanolichen biomass has been has been conservatively estimated to represent 100 kg ha-1 to 350 kg ha-1. While these estimates are small relative to that of woody plants, all of this biomass is photosynthetic, which means that despite their small biomass, cyanolichens likely play a significant role in forest functioning. The large surface area and porous structure allow lichens to capturing nutrients that would not otherwise be retained. In addition, cyanolichens are capable of Nitrogen-fixation, thereby providing a source of fixed-nitrogen to generally N-limited forest ecosystems.
The presence of epiphytic cyanolichens in the Inland Rainforest depends on the temporal continuity and climatic stability provided by old-growth stands. However there are patterns in cyanolichen communities within individual stands that are apparently not explained by stand age or moisture regime. In an effort to both characterize these community patterns and to provide insight into the potential deterministic factors, we documented the macrolichen flora at 9 field sites within the Sub-boreal spruce biogeoclimatic zone. These 9 sites were spread across a climatic gradient from very wet sites in the SBSvk to drier sites in the SBSwk. Macrolichens were recorded on saplings (<10 cm DBH) growing beneath the canopy of 5 tree species; poplar, birch, subalpine fir, spruce and Douglas-fir. Light availability (using hemispherical photography), temperature, relative humidity, soil nutrient availability, soil pH, and bark pH were also recorded beneath each of the 5 tree species. Our results demonstrate that cyanolichens are both more abundant and more diverse on poplar than beneath any other tree species. Furthermore, cyanolichen are more diverse beneath poplar than all other tree species regardless of the subzone, indicating that the role of poplar trees in determining cyanolichen communities is as, or more important that moisture regime. The factors that contribute to this apparently facilitative role of poplar trees remain unknown. None of the measured environmental variables were well correlated with the observed patterns in cyanolichen diversity and were thus not likely to be deterministic factors. Similarly, although differences in diversity between species of host-tree (phorophyte) have previously been attributed to chemical or climatic factors associated with the bark surface on which the lichen is found, these factors are unlikely to explain the influence of a distant tree crown. It is, however, likely that chemical factors - such as nutrient availability - play a pivotal role in providing cyanolichen habitat beneath poplar trees but further research is required.
1 Faculty of Forestry, University of British Columbia, Vancouver, BC. V6T 1Z4. Email: email@example.com
2 Department of Botany, University of British Columbia, Vancouver, BC. V6T 1Z4
3 Faculty of Forestry, University of British Columbia, Vancouver, BC. V6T 1Z4
4 Ecosystem Science and Management, University of Northern British Columbia, Prince George, BC. V2N 4Z9
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