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 pub lished fire history data (Payette et al. 1989), and field observations were used to examine the influence of caribou grazing in part of thei r lichen-dominated wintering grounds in northern Quebec, Canada. Liche n biomass and percentage ground cover were measured in 1989 and 1992 o ver a large area (88 150 km(2)) stratified into five postfire successi onal stages. 2. Lichen-dominated vegetation covered 55%, moss- or shru b-dominated vegetation 25%, and water bodies 20% of the study area. Li chen 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 a veraged 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 o ccurred at a rate of about 5% per year. No significant change in liche n cover was observed in younger stands. 3. The number of caribou grazi ng in the study area between 1989 and 1992 exceeded the carrying capac ity estimated from the annual increment in lichen biomass (approximate to 1% year(-1)); lichens were reduced by both consumption and collate ral damage. Lichen cover can be progressively reduced by winter grazin g of caribou in large lichen-dominated continental areas in much the s ame 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 wi ld caribou.