Growth performance of Cladina stellaris following caribou disturbance in subarctic Quebec1

Abstract: Cladina stellaris is a dominant lichen species of old-growth lichen-spruce woodlands in subarctic Québec, where the continuous lichen carpet persists for several decades in the absence of disturbance. The lichen carpet is, however, vulnerable to caribou (Rangifer tarandus) disturbance under dry site conditions. Through grazing and trampling, large herds of migratory caribou reduce C. stellaris abundance and modify ground vegetation composition. Here, we have evaluated the age and growth performance of C. stellaris in relation to the recent activity of the George River Caribou Herd (GRCH). We measured the age, length, and growth rate of C. stellaris podetia in and near caribou trails in 15 lichen-spruce woodlands across the summer habitat. The age of lichens, used to evaluate the initial period of lichen recruitment following the decline of the GRCH, indicated that lichen recovery began in the early 1990s in heavily disturbed sites, whereas comparisons between the age structure of border and trail lichens also suggested that the southern part of the calving ground was still heavily used in the early 1990s. Length and growth rate of C. stellaris thallus were closely associated with severity of caribou disturbance, as inferred from the residual ground cover of terrestrial lichens. Growth performance of C. stellaris during the initial stage of lichen recovery varied according to the spatial use of the summer habitat by caribou, with better performance at the edge of the summer and winter habitats and reduced performance in the extensively used calving ground. The analysis of growth performance of C. stellaris provides new insights on lichen-spruce stand recovery associated with caribou disturbance.

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