I recently spent some time on Quadra Island, B.C., on the east side of Vancouver Island, about half the way up. It's about 50 km long and 10-30 km wide. It seemed to me that the southern half of of the island is very poor in lichens (diversity, cover, biomass, etc.), while the northern part seems to have normal lichens for the PNW. Why are the lichens are so reduced in the southern part?
Both conifers and hardwoods have sparse lichens in the southern parts of the island. I would expect dense young stands to be nearly barren of lichens anywhere in the PNW, but even places with more open forest structure were strangely barren on Quadra Island. Crustose lichens appeared to be suppressed too. For example, you can find stabilized beach logs high on the shore tend to have hardly any Xylographa, Lecanora, or other expected species. Some trees are dense with monospecies stands of Ramalina farinacea but almost nothing else.
Air pollution? I saw no sign of industry nearby, but perhaps there was historic air pollution?
Forest management? Perhaps the whole southern part was clearcut over a short period of time, creating a deficit of nearby propagule sources. The northern part has more rocky knobs and outcrop areas that haven't been logged. Perhaps the logging was less thorough in the north.
I only spent a week there, so my observations may be off base. Maybe others can confirm or refute these impressions. Or maybe you have some clues to help solve the mystery.
