Prolonged hydration severely limits CO2 diffusion to the photobiont and, therefore, photosynthesis of lichens (Lange et al. 1993, 2000; Zotz et al. 1998). In contrast, many bryophytes can thrive under continuously wet conditions (Proctor 2000). Thus, bryophyte biomass is generally highest in rainforests, cyanolichens reach their greatest abundance in moist forests with a summer dry season, and chlorolichens are often the only epiphytes in dry forests.