Decline of the globally rare old-growth specklebelly lichen, Pseudocyphellaria rainierensis, and its implications for temperate rainforest conservation

Epiphytic lichens are key components of temperate rainforests, where they contribute to forest hydrology, nutrient cycles, food webs, and overall biomass and biodiversity. Despite their ecological importance and sensitivity to environmental change few protections exist for lichen conservation and management. Pseudocyphellaria rainierensis, or old-growth specklebelly lichen, is considered an important indicator of high conservation value, temperate rainforest in the Pacific Northwest bioregion of North America. Concerns about continued habitat destruction and recent population losses due to wildfires prompted us to investigate the status of P. rainierensis. We gathered all known historical records of the species and conducted an extensive population assessment in Washington state. We revisited 31 of the 143 historical sites (22%) and did not recover P. rainierensis at 13 sites, indicating that populations declined by 41%. Our analysis of Forest Inventory and Analysis (FIA) data revealed the presence of P. rainierensis in eight of 664 forest plots surveyed over a 20-year period. During field surveys we discovered four new sites and a review of records from the community science database, iNaturalist, identified eight new sites. Our findings underscore the critical need to regularly monitor old-growth dependent lichen populations and plan for strategic surveys to identify potential new locations where these species may occur. Our study offers a model for successful monitoring of rare species through public-private partnerships and engagement with community science efforts. Using these methods, forest managers and policy makers can utilize the best available scientific information for making conservation decisions.