COS 99-6 - Sounding the alarm: Rare lichens may be rapidly declining in the Pacific Northwest

Abstract: Lichens, critical members of terrestrial ecosystems globally, may be particularly sensitive to global change pressures because they respond to the environment at fine scales. Losses of lichen diversity and biomass will likely disrupt food webs and alter nutrient cycles. Because lichens do not have known adaptations to wildfire, altered fire regimes pose a particular risk to lichens. Wildfires may catalyze range shifts by settling the "climate debt" of lichen communities that are currently at the edge of their thermal limits. Government rarity rankings for lichens in the United State and Canada are generally based on the assumption that lichen populations observed in a single historical survey remain extant, but if wildfires and other global change pressures have caused widespread extirpations of lichen populations, extinction risks of numerous lichens species may be much greater than previously estimated. In this study, we use spatial analyses to estimate the proportion of rare lichen populations that have likely been extirpated because of recent wildfires in Oregon and Washington, USA. We also perform an analysis of long-term population trends in the old-growth-forest-associated lichen based on field observations and assessments of changes in habitat quality.

We found that as many as approximately one-third of rare lichen populations in Oregon and Washington, USA, may have experienced wildfires in the last 20 years. While exact extirpation rates cannot be calculated without field visits, as many as one quarter of known rare lichen populations may have been extirpated in these wildfires given that lichens rarely survive high severity fire. In our case study with a rare old growth forest lichen, we estimate 35-45% population declines across all previously known populations, largely because of wildfire, logging, and other forms of habitat degradation. Our findings highlight that rare lichen rankings in the Pacific Northwest, and likely globally, should be reevaluated in light of effects of widespread, recent wildfires and other global change pressures. Extinction risks for lichens may be greater than previously estimated, and major range contractions may have already occurred for some species. Extensive field monitoring will be critical for providing more specific data on the status of rare lichen species. There may be little time remaining to save some of the most vulnerable lichens in the Pacific Northwest.