Quantifying changes in annual lichen volume for woodland caribou in Newfoundland using Landsat time series

Terrestrial and arboreal lichen are the primary winter food source of the threatened boreal ecotype of woodland caribou ( Rangifer tarandus caribou ). Despite its essential role, lichen biomass, a key factor of caribou habitat suitability, remains poorly quantified in forested landscapes, limiting effective habitat management and recovery planning. Our objective was to estimate lichen volume across two Newfoundland (Canada) boreal caribou herd ranges (Gros Morne and Gaff Topsails) using vegetation-specific models that integrate 1984–2022 Landsat Best Available Pixel composites with annual vegetation classifications from the National Terrestrial Ecosystem Monitoring System. Field data from 66 plots informed zero-inflated gamma models for coniferous forests, wetlands, barren land and shrublands. Predictors included spectral reflectance, vegetation indices, and vegetation type interactions. Model predictions closely matched observed lichen volume (pooled R 2 = 0.77, RMSE = 8.58 dm 3 m −2 ). Spatial outputs revealed widespread low lichen volume, with the highest volume in coniferous forests. Temporal trends showed a general increase in lichen volume since the early 1990s, with faster recovery across Gros Morne—potentially aided by the protected national park—compared to the more disturbed Gaff Topsails, where historical disturbances could have slowed early recovery. Estimated lichen biomass showed that patches reaching ∼3000 kg·ha −1 —a level typical of stands preferentially used by caribou in winter—were rare but widely distributed across the landscape. These vegetation-stratified, long-term estimates of lichen volume provide a key tool for assessing habitat suitability and guiding conservation strategies aimed at supporting woodland caribou recovery across Newfoundland.