Estimating lichen biomass and caribou grazing on the wintering grounds of northern Quebec: An application of fire history and Landsat data

1. Landsat Thematic Mapper (TM) remote sensing imagery, previously published fire history data (Payette et al. 1989), and field observations were used to examine the influence of caribou grazing in part of their lichen-dominated wintering grounds in northern Quebec, Canada. Lichen biomass and percentage ground cover were measured in 1989 and 1992 over a large area (88 150 km(2)) stratified into five postfire successional stages. 2. Lichen-dominated vegetation covered 55%, moss- or shrub-dominated vegetation 25%, and water bodies 20% of the study area. Lichen biomass increased with postfire stand age, from 530 kg ha(-1) in young stands (<30 years) to 8010 kg ha(-1) in old stands (>90 years). The cumulative amount of lichen cover removed by caribou before 1989 averaged 10% over the study area; by 1992 this value had risen to 21%. Between 1989 and 1992, ground cover of lichens decreased from 55 to 42%. Lichen removal was concentrated in stands >50 years old, where it occurred at a rate of about 5% per year. No significant change in lichen cover was observed in younger stands. 3. The number of caribou grazing in the study area between 1989 and 1992 exceeded the carrying capacity estimated from the annual increment in lichen biomass (approximate to 1% year(-1)); lichens were reduced by both consumption and collateral damage. Lichen cover can be progressively reduced by winter grazing of caribou in large lichen-dominated continental areas in much the same way as in insular ranges. 4. The combination of remote sensed and fire history data may be a helpful tool for managing large herds of wild caribou.