A comparison of Lobaria pulmonaria population structure between subalpine fir (Abies lasiocarpa) and mountain alder (Alnus incana) host-tree species in British Columbia’s inland temperate rainforest

Abstract

In a study using dated branch segments, we determined the size class distribution and reproductive status of Lobaria pulmonaria (L.) Hoffm. growing on subalpine fir (Abies lasiocarpa Nutt.) and mountain alder (Alnus incana (L.) Moench) alongside small streams in British Columbia’s inland temperate rainforest (ITR). The number of thalli per branch segment did not significantly differ between Abies and Alnus, although mean L. pulmonaria biomass on entire branches was 71.03 g on fir and 12.31 g on alder. Branch diameter was a significant predictor for reproductive status of thalli on fir, whereas branch age was a better predictor for thalli on mountain alder. The presence of sorediate and (or) isidiate individuals on branch segments <10 years old suggests a rapid generation time for L. pulmonaria in the ITR. Annual growth rates of L. pulmonaria thalli reached up to 1.16 cm2·cm−2·yr−1 on branch segments less than 15 years in age. Specific thallus mass (STM) was significantly higher for thalli on alder. STM was strongly dependent on thallus size on both host-tree species, with values from above 10 mg.cm−2 in large thalli (>100 cm2), to <3 mg.cm−2 in small thalli (<0.1 cm2). These differences between host-tree species can be interpreted in context of both adjacent canopy structure and the differences in tree growth form between these two host-tree species, both of which factors lead to greater light availability at the surface of mountain alder branches. The fast growth rates and short generation time observed in L. pulmonaria thalli growing on both alder and fir highlights the favorable conditions riparian habitats create for lichen growth in British Columbia’s ITR.