Size is a main driver for hydration traits in cyano- and cephalolichens of boreal rainforest canopies

We measured the water holding capacity per area (WHCA; mg H2O cm−2), and thus the saturating rainfall (mm), for sympatric cyano- (Lobaria scrobiculata and Pseudocyphellaria crocata) and cephalolichens (Lobaria pulmonaria) along canopy height gradients in boreal rainforests, to quantify the importance of specimen size, photobiont type and branch height as WHCA drivers. Size increased WHCA by a factor of four. Cyanolichens had ≈1.5 times higher WHCA than cephalolichens. Finally, branch height significantly increased WHCA for the Lobaria species. Reported responses are consistent with higher optimal rainfall requirements for reproducing versus juvenile specimens, and for cyanolichens versus those with green algal photobionts. Increased WHCA with height in the canopy is consistent with acclimation to stronger evaporative demands. The results highlight the link between rainfall patterns and maximal sizes realized for a given lichen species and habitat, and extend our understanding of why the cyanolichen/green algal lichen-ratio increases in forests with increasing rainfall.