The globally threatened epiphytic cyanolichenErioderma pedicellatumdepends on a rare combination of habitat factors

Abstract

Lichen extinction occurs at rapid rates as a result of human activity, although species could potentially be rescued by conservation management based on ecophysiological knowledge. The boreal old forest cyanolichen Erioderma pedicellatum currently occurs in few sites worldwide. To protect it from extinction, it is essential to learn more about it. The last remaining good European site is a canyon with a waterfall, in a low-rainfall region of Norway. Here, a spatially restricted population of 1500–2000 thalli dominates the epiphytic vegetation of a small number of Picea abies canopies. We were able to document that 1) E. pedicellatum grew on thin branches with higher bark pH than is normal for P. abies in a canyon that provided an unusual combination of very high light, high air humidity, and cool temperatures in the growing season. However, the species did not inhabit the main waterfall spray zone. 2) Erioderma pedicellatum had a high light saturation point, high CO2 uptake at high light (≥ 600 μmol m−2 s−1) and cool temperatures (5–20 °C), and experienced strong suprasaturation depression of photosynthesis when fully hydrated. 3) It showed good tolerance of desiccation and high light; it was slightly more tolerant than the morphologically similar, but more common cyanolichen Pectenia plumbea. 4) The European population in its sunny habitat had higher water holding capacity than previously recorded in slightly shaded rainforest populations in Newfoundland, consistent with acclimation to compensate for high evaporative demands. Understanding the ecological niche and responses to critical environmental factors is essential for action plans to avoid extinction of E. pedicellatum. Methods used in this study could also be applicable for ecological understanding of other threatened lichen species.

Factors influencing the distributions of two endangered lichens in Nova Scotia, Canada

“…Both lichens showed a positive logistic relationship with the number of rainy days; this confirms the theory that frequent inputs of liquid water (as rain or fog) are especially important for cyanolichens (Gauslaa 2014). Other recent work confirmed this experimentally, demonstrating that significant inputs of liquid water (≥1.7 mm, Gauslaa and Arsenault 2020), or fine water droplets such as those generated in proximity to waterfalls (Nilsson et al 2022), are required for E. pedicellatum to maintain full thallus hydration. Erioderma mollisimum showed a stronger association with high mean annual rainfall than E. pedicellatum, but moderate mean annual snowfall was exclusively associated with Erioderma pedicellatum.…”

“…Acer rubrum and Abies balsamea are both adapted to growing in acidic environments (i.e., peatlands) but are known for having less acidic bark than most co-occurring tree species (COSEWIC 2002); this buffering capacity of the bark would further delay any negative impacts on lichens beyond the point at which soil buffer capacities become exceeded (sensu Gilbert 1970). Recent measurements in forested wetlands of southwest Nova Scotia have confirmed that, at least with Acer rubrum bark, some buffering ability is likely still present, with pH values of 4-5 (Haughian, unpublished data), and research from other regions has shown a consistent association between Erioderma occupancy and high bark pH, even within a host tree (Nilsson et al 2022). On the other hand, the inputs of acid pollution that were incorporated into the acid threshold exceedance estimates originated from raster layers with a grid cell size of 35 × 35 km (Carou et al 2008), leading to a considerable homogenization over such a small area as Nova Scotia.…”

“…Old forested wetlands that host Erioderma species also tend to have a more open forest canopy than upland forests in Nova Scotia, leading to increased light (Cameron and Neily 2008; Power et al 2018). Recent research has shown that Erioderma pedicellatum has a relatively high light saturation point, reflecting an adaptation to more exposed habitats (Nilsson et al 2022). Given the wide ecological amplitude of the host trees for Erioderma species, the presence of a host tree alone would have been a poor predictor of habitat suitability.…”

Habitat associations of red-listed epiphytic lichens in Finland

“…Thus, the occurrence of many lichens, as indicated by our results, may be dependent on intermediate conditions where both humidity and light availability are at least moderate (Gauslaa et al 2006). Our data suggests that some species prefer an unusual combination of high humidity and high light availability (see also Nilsson et al 2022). Our results highlight that dense forests are inhospitable to many red-listed lichens (see also Gauslaa et al 2006;Gauslaa et al 2007;Klein et al 2020;Nirhamo et al 2021).…”