Long-term fluctuations of a caribou population revealed by tree-ring data

Abstract

We used a dendroecological approach that involved examination of debarking lesions (trampling scars) produced by caribou (Rangifer tarandus) hooves on surficial roots and low branches of conifers to assess caribou activity in the summer range of the Rivière George caribou herd in northeastern Quebec-Labrador over the last 100 years. We deduced changes in caribou activity from the age-frequency distributions of trampling scars in three widely spaced (>100 km) old-growth conifer stands in the Rivière George area. We used the fluctuating patterns in age distributions, described by residuals of the log-linear regression, as an index of the number of trampling scars with time. This index indicated that caribou activity at the three sites followed a general decreasing trend from the turn of the last century to around 1950. There were two stages of rapid decline, around 1905-1915 and 1940, separated by a minor increase in the 1920-1930s. A sustained increase occurred from the 1950s to the 1980s. A comparison with survey and historical data for caribou suggested that these fluctuations in this common signal of activity at the three sites resulted mainly from fluctuations in caribou abundance that occurred throughout the 20th century in northeastern Quebec-Labrador. The increase in caribou activity during the 1920-1930s suggested by the frequency of trampling scars is not reported in the historical record. Caribou trampling scars on conifers may offer a new opportunity to assess large-scale spatial and temporal population trends of caribou in subarctic and boreal zones.