E-mail : claude.morneau@mrn.gouv.qc.ca

Dendroecological analysis of caribou activity and vegetation disturbance in northeastern Québec
Supervisor : Serge Payette

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The George River caribou herd grew from 12 to 17% a year over a 30-year period (1954-1984) before stabilizing at around 700,000 individuals. We studied the influence of caribou browsing and trampling on vegetation of calving grounds and summer ranges over the last several decades. Mapping of spruce lichen-spruce woodland and lichen mats was conducted in 1992 and 1993 using aerial transects in order to determine three zones of different groundcover degradation. A severely degraded zone, characterized by the absence of the lichen carpet and presence of bare soil at nearly all of the sites, extends over approximately 40,000 km² of the tundra region in northeastern Québec-Labrador. The degree of degradation of the ground cover diminishes progressively through a transition  zone of around 40,000 km². This third zone is dominated by less-disturbed Cladina stellaris cover within the forested sectors along the border of the summer range. Dead vegetation in spruce lichen woodlands within the severely degraded zone and the transition zone indicates that vegetation changes are of recent origin (~10 to 15 years) and correspond to the degradation of a well developed C. stellaris mat. A new dendroecological approach was used to evaluate the frequency of summertime caribou traffic in lichen woodlands by determining the age structure of trampling scars. These scars form on superficial roots and low-lying branches of conifer trees when they are damaged by caribou hooves. Scar data were used to reconstruct changes in the summer range activity of the George River caribou herd. The spatiotemporal patterns of caribou activity were reconstructed a chronology of trampling scar age structure from 33 old-growth (> 150 years) lichen woodlands. The main changes in caribou activity are strongly related to the demographic trends of the herd, as determined by aerial surveys. Our results suggest that the growth of the herd slowed considerably around 1980 and then declined slightly between 1988 and 1992. These trends were not detected in the aerial surveys. The reconstruction of the recent activity patterns and the analysis of the conditions of the groundcover indicate that the main vegetation changes in the study area occurred during the 1980s, and correspond to a marked increase in caribou activity between 1982 and 1985 in the severely degraded vegetation zone. Changes in caribou activity since the end of the 19th century were also evaluated. The age structure of trampling scars show synchronous activity at three lichen woodland sites located 100 km from each other. This common signal, which extends across the sites, suggests two periods of rapid caribou decline (1905-1915 and 1935-1945) interrupted by a period of population growth during the 1920s and early 1930s. This pattern of caribou activity is more complex than that derived from historical records, which did not show caribou growth during the 1920-1930s. Low caribou activity during the last 100 years occurred in the 1940-1950s. In conclusion, spatiotemporal variations of caribou populations can be reconstructed with the aid of trampling scars on conifer roots and branches. This method allows the reconstruction of caribou activity over a period that extends well before that of the first caribou inventories.


Publications

Payette, S., Boudreau, S., Morneau, C., Pitre, N., 2004. Long-term interactions between migratory caribou, wildfires and Nunavik hunters inferred from tree rings. Ambio, 33: 482-486.


Boudreau, S., Payette, S., Morneau, C., Couturier, S., 2003. Recent decline of the George River caribou herd as revealed by tree-ring analysis. Arctic, Antarctic, and Alpine Research, 35: 187-195.


Morneau, C., Payette, S., 2000. Long-term fluctuations of a caribou population revealed by tree-ring data. Canadian Journal of Zoology, 78: 1784-1790.

Morneau, C., Payette, S., 1998. A dendroecological method to evaluate past caribou (Rangifer tarandus L.) activity. Écoscience 5: 64-76.