December 19, 2006

A Christmas Caribou Story

Filed under: Adaptation, Animals

Santa has his sleigh pulled and magically flown each year by Rudolph and his reindeer buddies, but Santa could just as easily select the local caribou for the same job. Given that global warming is expected to impact high latitude locations of the Northern Hemisphere more than the rest of the world, one might fairly asked how the herds of animals of Santa’s world are coping with the elevated carbon dioxide levels.

If you Google “Global Warming and Reindeer”, you will be led to 180,000 sites, but if you Google “Global Warming and Caribou”, you will find an astounding 230,000 sites. You will read that these animals cannot tolerate warmer temperatures that impact the calving season, you will discover that their food sources are in disarray, you will even read that recent heavy snows have crippled the herds, and the heavy snow is related to global warming causing more evaporation worldwide (“Good-bye to Rudolph” is a repeated theme, and sure to resonate with children). If you saw the Gore film, you will certainly recall the attention paid to polar bears drowning as they become trapped on small blocks of ice … the animals of the polar and tundra areas seem doomed, all because we will not “do something” about emissions of greenhouse gases.

In seeking good news for the holiday season, we found an interesting article in the recent issue of Arctic, Antarctic, and Alpine Research dealing with caribou herds of the Northwest Territories of Canada. A team of high-latitude specialists from the University of British Columbia and the Western Territories’ Department of Environment and Natural Resources studied the size of the herds through time, and incredibly came up with a method to estimate herd size over the timescale of centuries.

Zalatan et al. begin their article noting that “Barren-ground caribou (Rangifer tarandus groenlandicus) tend to undergo relatively regular changes in population size over decadal time scales.” It seems right away as if caribou herds grow and shrink in numbers quite naturally, but surely the herds have suffered during the last 100 years of greenhouse gas buildup? They also note that “Caribou abundance among different herds has been shown to be in synchrony at continental scales” and changes in climate can certainly impact the herds at continental scales. So if we only knew the sizes of the herds through time, we could detect how changes in climate impact the caribou.

Well, the evolving science of dendroecology has provided such a method to describe changes in caribou abundance over many decades. The trick is to look at the trees, particularly “the scars left by caribou hooves on the top of surficial roots or low branches of spruce trees during their spring and summer migrations.” More specifically, they note that “The scars are formed when part of the bark is removed due to trampling, which causes cambium death and stops radial growth in that section of the root. A scar lobe forms around the damaged cambial tissue in subsequent years.” Similar to counting back tree rings to find individual years in the past, the scar formation can be accurately determined using the same approach. Zalatan et al. conclude “This method has made it possible to reconstruct caribou population activity and provides the longest proxy record for changes in caribou herd size.”

The sampling of the spruce roots took place in the forest-tundra near Yellowknife and the Great Slave Lake. They used “local knowledge” by working with elders of the local Dogrib peoples, and from what they learned, they selected fifteen study sites across the treeline that were frequented by caribou. They broke the sites up into a northwest group and a southeast group, and they note that the “scar frequencies for both groups of sites showed the same patterns of major increases and decreases.”

In describing the variations in herd size over the past century, and the team concludes that “All sites showed low numbers until the 1920s, again from 1955 to 1970 and in 2000.” We speculate that the drop in 2000 was related to heavy snow or more likely, the immediate response of Gore’s defeat in that year. However, the “scars showed an increase in caribou numbers during the 1940s until the mid-1950s, and from 1980 to 2000.” Imagine that, the caribou herds increased “from 1980 to 2000” and during the time the great global warming scare picked up all of its momentum.

Zalatan et al. show that “Both groups of sites showed similar patterns in scar frequency, indicating that the different herds within the sampling area experienced similar changes in abundance over time. Given the scale of these synchronous changes in caribou abundance, it is likely they are linked to changes and variability in large-scale climate, such as the Arctic Oscillation.” They never mention global warming, we cannot help but notice absolutely no trend in herd size over 100 years, and any downturn in 2000 was equaled or eclipsed back in 1920.

The first author’s name, Zalatan, sounds to us like some mystical performer in Las Vegas, and true to the rule to always leave the audience wanting more and more, they conclude “We investigate the link between the abundance patterns and climate in a future study.” World Climate Report will be there when the next Zalatan piece hits the big stage!

Reference:

Zalatan, R., A. Gunn, G. H. R. Henry, 2006. Long-term Abundance Patterns of Barren-ground Caribou Using Trampling Scars on Roots of Picea mariana in the Northwest Territories, Canada. Arctic, Antarctic, and Alpine Research, 38, 624–630.




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