The influence of wind and light exposure on the extent of lichen coverage in an alpine environment

Lichens are important components of arctic and alpine ecosystems. Their abundance and diversity are high despite the harsh conditions, yet little is known about the microclimates that favour lichen growth. Using a 2 x 2 factorial design, we classified rock faces at the high alpine Barcroft Field Station in the White Mountains of California into high and low wind exposure and high and low light exposure categories. We then measured the extent of coverage of two alpine crustose lichen species, Caloplaca ignea and Pleosidium flavum, on the rock faces. The data show that lichen coverage is greatest on rock faces that are protected from wind but exposed to light (median = 60 m2, range = 1.8 - 647.1 m2), and lowest on faces that are exposed to wind but protected from light (median = 7.4 m2, range = 0.15 - 142.5 m2). The lack of success in high wind conditions may be due to desiccation-induced inhibition of photosynthesis, leading to reduced carbon balance in wind-exposed lichens. By characterizing favourable microclimates, this study provides observational data that help to establish the environmental dependence of photosynthesis and respiration in cold climate lichens. This is particularly important for informing estimates of ecosystem-level carbon balance in regions like the boreal, where lichens represent 50-90% of vegetation cover.