Climatic changes and caribou abundance in northern Québec over the last century

The temperature increase observed in the Northern hemisphere during the first half of this century was also detectable in Québec; it affected both summer and winter. In northern Québec, warmer summers stimulated growth and favored range expansion of trees and shurbs. Based on black spruce krumm¬ holz height and water level in lakes, the warmer period was also characterized by greater snowfall and deeper snow cover. This period of deep snow coincided with apparent caribou scarcity. Three hypotheses were explored to relate increased temperature with caribou decline: 1) destruction of winter habitat due to high frequency of forest fires, 2) increased energy cost to obtain forage in deep snow and 3) delayed melting of snow on calving grounds that shortened the time to raise calves. The combined effect of the 3 mechanism could explain caribou scarcity, particularly for the Rivière George herd whose calving ground becomes snow free in late June. Ways to test the third hypothesis are proposed.


Introduction
Various factors have caused continuous changes of earth's climate over geological time (Harrington 1987).The temperature increase obeserved in the Northern Hemisphere during the first half of the 20th century was associated with reduced volcanic activities (Harrington 1987).Vegetation of northern Québec reacted to warm summers during this period: growth of black spruce (Picea mariana) was better than during the preceding 5 centuries (Payette et al. 1985), and green alder (Alms crispa), tamarack  (Meldgaard 1986).In northern Québec, mean snow depth may have increased by 20 cm during this period (Payette et al. 1985).
Even if quantitative information remains unavailable for most of the period, caribou numbers have fluctuated drastically over the last 100 years.They were seemingly plentiful at the turn of the century but became suddenly scarce until 1950-1960(Audet 1979)).During the following decades, the Rivière George herd increased at an annual rate exceeding 10 percent (Messier et al. 1988), to reach 682 000 (S.E.= 145000; n=81) individuals in 1988 (Crête et al. 1989).Calf production has diminished by 20 percent since 1984 (Messier et al. 1988) and the herd may be leveling off or decreasing (Crête et al. 1989;Hearn et al. in press.).The Rivière aux Feuilles herd, the other herd calving on the Québec tundra, was made up of more than 100 000 individuals in 1986 (Crête et al. 1987); animals are in excellent condition (unpubl.), but the population dynamics of this herd remain unknown.Comparable fluctuations in caribou numbers with peak density by 1900 and in recent decades were also reported for Greenland (Meldgaard 1986).We examined climatic changes over the last 100 years in relation to fluctuation of caribou abundance.
We tried to find relationships between temperature warming and caribou scarcity.We investigated the following hypotheses: 1) the incidence of forest fire was higher during the first half of the century, particularly in the north of the boreal forest so that caribou prime winter habitat became limited; 2) snow cover was deeper during this period and incidence of winter rain was higher so that forage was more difficult to obtain; 3) deeper snow cover delayed snow melt in spring so that emergence of green vegetation came later on calving grounds.

Study area and methods
The calving ground of the Rivère George herd is located east of Kuujjuaq on a tundra plateau which ranges in altitude between 500-750 m.
(Fig. 1.).Before the mid-seventies, the herd used to spend the snow-free period in the vicinity of the calving area and migrate south and   and Kuujjuaq (1947Kuujjuaq ( -1986) (Fig. 1).
Monthly temperature averages and total snowfall and rainfall served as input data.The year was divided into periods, November -April and   there than further west due to greater precipitations and numerous fire breaks (Foster 1983).

Increased difficulty of obtaining winter forage
Cost of locomotion increases exponentially with snow depth in cervids (Mattfeld 1973;Fancy 1986) as is the energy spent by caribou digging in the snow to reach forage (Fancy 1986).In particular, the presence of ice crust may be very detrimental.Increased snow depth during the first half of the century certainly inflated the annual energy budget of caribou.No massive caribou die-off was reported during winter in northern Québec for this period, but it could have gone unnoticed in this vast and unaccessible area.Caribou of the Rivière George herd, particularly lactating females, actually enter the winter with limited fat reserve (Huot 1989) due to poor summer range (unpubl.);however they do not exhaust their fat store in winter because of a good winter range (Huot 1989).Increased energy demand for winter foraging would be actually detrimental to the herd productivity.

Effect of delayed snow melting on calving grounds
Actually, caribou from northern Québec appear to find enough energy in their forage during winter, wich however is deficient in protein (Huot 1989).Forage rich in protein is necessary to complete gestation and to nurse calves in cervids (Smith et al. 1975;Sadleir 1980) < 20 in 1984< 20 in , 1986< 20 in and 1987< 20 in respectively (Crête et al. 1987;;Vandal and Couturier 1988).At the Rivière aux Feuilles calving ground, snow covered 34 percent of the ground on June 3, 1986 (Crête et al. 1987).In general, snow melts more rapidly on the Ungava peninsula than along the Rivière George as illustrated satellite images taken in late June 1985 and 1986 (Fig. 3).Greater snowfall in the past could have resulted in complete snow cover on the Rivière George calving area until late June and early July, which would leave too short a period for females to successfully complete an annual cycle there.

(
Larix laricina) and white spruce (Picea glauca) exhibited range expansion at the tree line (Gil-Rangifer, Special Issue No. 3, 1990: 159-165 bert and Payette 1982; Morin and Payette 1984; Payette and Filion 1985).Such vegetation response must mainly have depended on longer and warmer growing seasons, but temperatute records in southern Québec since 1876 indicate that the warming trend also occured in winter.Warm winters during the first half of the century in Greenland were apparently caused by a displacement of the polar front; they were characterized by greater snowfall and rainfall

Fig.
Fig. It Location of the 3 weather stations from which meteorogical data were analysed, distribution of the tundra in northern Québec and calving grounds used in 1986 by the Rivière aux Feuilles caribou herd (west) and the Rivière George herd (east).

Fig. 3 .
Fig. 3. Distribution of the remaining snow cover in northern Québec on June 18, 1985 and June 26, 1986 according to visual interpretation of NOAA/AVHRR satellite image (St-Pierre et al. 1987).

Table 1
(Vandal and Couturier 1988)1984t matrix computed with annual winter and summer average temperatures between 3 weather station inQuébec, 1946Québec,  -1948Québec,   to 1986.All coefficients significant (P<0.02).anumber of years comparedMay -October.In addition NOAA/AVHRR satellite images were used to examine snow cover disappearance between 1980 and 1986 over northern Québec(St-Pierre et al. 1987).In 1984 and 1986, vertical aerial photographswere used to determine percent snow cover during calving(Crête et al. 1987); in 1987, visual estimation was made from an aircraft flying 200-300 m above the ground(Vandal and Couturier 1988).

1871 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 YEAR
ville and Kuujjuaq (Table1).The strength of the relationship was greater for Kuujjuaq and Schefferville that are relatively close, than for Québec City and 2 other areas; the relationship between the 3 weather stations was slightly closer for summer than winter temperature.On the other hand, no significant (P>0.1)relationship was found for winter snowfall or rainfall between Québec City and Schefferville or Kuujjuaq.We concluded that the temperature trend in northern Québec during the last century could be extrapolated from Québec City, but not precipitation trends.