Background/Question/Methods Evaluating the conservation value of ecological communities is critical for forest management but can be challenging because it is difficult to survey all taxonomic groups. Lichens have long been used as indicators of late successional habitats with particularly high conservation value because lichens are ubiquitous, sensitive to fine-scale environmental variation, and some species require old substrates. However, the efficacy of such lichen indicator systems has rarely been tested across broad geographic regions, and their reliability has not been established with well-replicated quantitative research. In this study, we develop a continuous lichen conservation index representing epiphytic macrolichen species affinities for late successional forests in the Pacific Northwest, USA. This index classifies species based on expert field experience and is similar to the coefficient of conservatism that is widely used for evaluating vascular plant communities in the central and eastern USA. We then use a large forest survey dataset from the Cascade Range of Oregon and Washington, USA, to test whether the community-level lichen conservation index is related to forest stand age. Results/Conclusions We find that the lichen conservation index has a positive, linear relationship with forest stand age when averaged at the community level. Our continuous ranking system appears to have substantial advantages over existing old forest lichen indicator systems that classify species as either old growth forest indicators or not. Our findings highlight that lichen communities can be useful indicators of late successional habitats of conservation concern, and that indicator systems based on expert experience can have strong biological relevance.