How Thermal Patterns Change During Dehydration in Non-Vascular Epiphytic Communities.

Lichens and bryophytes, as poikilohydric and poikilothermic organisms, reach equilibrium with their surroundings. However, non-vascular epiphytic communities contribute to ecosystem functions, such as water and energy balance, by interacting with the environment through water and heat exchange at the substrate-atmosphere interface. We hypothesized that variations in water content during dehydration cycles could alter thermal patterns, leading to greater thermal heterogeneity associated with increased life-form diversity. We captured infrared images of eight bark sample categories representing different epiphytic community compositions. Using structural equation modeling, we analyzed how epiphytic community composition influenced thermal patterns, both directly and indirectly, through water-related variables. Our findings indicate that foliose lichens and bryophytes exhibited similar water and thermal trends. Both life forms, characterized by higher water content (WC), negatively affected thermal variables. In contrast, crustose lichens had opposing effects on WC and thermal dynamics. From the saturation point, the average WC over five sessions remained above 50% in samples colonized solely by foliose lichens or bryophytes and nearly 80% in those with both. In contrast, samples dominated by crustose lichens had an average WC below 20%. Bark samples with higher bryophyte and foliose lichen cover retained water for longer, whereas those dominated by crustose lichens lost water more rapidly. Regarding temperature, bryophytes and foliose lichens started at approximately 12°C, with mean final temperatures of 13.7°C and 14.4°C, respectively. Crustose lichens had a higher mean initial temperature of 12.5°C and a final temperature of 16.65°C. These differences may be explained by morphological traits, such as the greater hydrophilic properties and higher surface-to-volume ratio of bryophytes and foliose lichens compared to the hydrophobic properties and lower surface-to-volume ratio of crustose lichens. This study underscores the importance of incorporating non-vascular epiphytic communities into ecological research aimed at elucidating the regulation of thermal and water dynamics at fine scale levels.