Upon their arrival in spring,
Snow Geese feed on the underground parts of various tundra plants.
Later in the summer, during the brood-rearing period, goose families
prefer to feed in wetlands, where they can graze on fresh grasses
Over the last 30 years, the Greater Snow Goose has seen its population
explode. One of the most concerning consequence of such population
expansion is the destruction, by overgrazing, of the Arctic habitats
they use during the breeding season. Indeed, destruction of large
marshes areas by the Lesser Snow Goose has been observed in La
Pérouse Bay, on the West Coast of the Hudson Bay (Canada).
Such dramatic impacts are not observed on Bylot Island yet, but
in order to identify the first signs of detrimental effects, our
project closely monitors the Bylot Island wetlands productivity
(how much plant mass is produced) and the goose grazing impacts
in those wetlands.
To monitor wetlands productivity and goose
grazing impacts, 36 exclosures are built each summer in 3
wetland areas of the island (Qarlikturvik
Valley, nesting colony, Pointe Dufour). Exclosures are
fenced areas of 1 m per 1 m, built with chicken wire, to
keep geese from grazing the vegetation. At the end of each
summer, our team samples the vegetation inside and outside
the exclosures. The amount (in grams) of vegetation inside
the exclosure (ungrazed) gives a measure of the wetlands
productivity for the year. In comparison, the difference
between the amount of vegetation inside and outside the exclosure
(ungazed vs grazed) gives an indication of the proportion
of vegetation grazed by geese during the summer.
Wetlands productivity is evaluated by measuring
the amount of above-ground biomass (mass of vegetation growing
above the ground) in ungrazed areas. When evaluating this productivity
on Bylot Island, plants are divided in 3 large groups: Eriophorum
(Cottongrass, the preferred plant of geese), Dupontia
(tundragrass, another plant favoured by geese) and total graminoids
(the 2 previous groups plus all other grassy plants). Forbs are
also weighted, but they are not considered here because they only
account for a really small portion of wetlands productivity.
of each plant group varies from year to year, influenced
by fluctuating environmental conditions. From 1990 to 2007,
above-ground biomass of graminoids averaged 45 g/m²
(grams per square meter) in the Qarlikturvik Valley (main
brood-rearing area). With an average of 28 g/m², Dupontia
accounted for 62% of this biomass. It was followed by Eriophorum
which produced an average biomass of 14 g/m², accounting
for 31% of the total graminoids biomass.
Since 1990, the biomasses of total graminoids,
Eriophorum and Dupontia have shown increasing
trends in the Qarlikturvik Valley. Indeed, since 1998, the
plant productivity has been generally higher than the long
Considering the years 1998 to 2007, the average above-ground
biomass of graminoids was 54 g/m² in the Qarlikturvik Valley.
Since the nesting colony and Pointe Dufour were only monitored
since 1998, this value can serve to compare the productivity of
the Qarlikturvik Valley with those of the two other areas.
With a total above-ground biomass of graminoids averaging 32
g/m² (1998 to 2007), plant productivity in the main nesting
goose colony is lower than that observed in the Qarlikturvik Valley.
Dupontia accounts for a large part (56%) of this biomass,
with an average 18 g/m². It is followed by Eriophorum
(38%) which produces an average 12 g/m². There are no detectable
temporal trends with biomass at the nesting colony. It is however
noteworthy that 1999, 2001 and 2007 were years of high plant productivity
in the nesting colony.
From 1998 to 2006, Pointe Dufour (another brood-rearing site)
tended to show slightly lower plant productivity than the Qarlikturvik
Valley. Its average above-ground biomass for all graminoids is
50 g/m². In Pointe Dufour, Dupontia had an average
above-ground biomass of 23 g/m² and Eriophorum,
13 g/m². These two plant groups accounted for respectively
46% and 26% of the total above-ground biomass of graminoids. As
for biomass in the nesting colony, there are no temporal trends
with the biomass at Pointe Dufour.
Goose Grazing Impacts
On Bylot Island, goose grazing impact is calculated as the proportion
of above-ground plant mass grazed by Greater Snow Geese. This
impact varies from year to year and is influenced by the number
of Snow Geese breeding on the island. Considering our data from
1990 to 2007, Greater Snow Geese removed, on average, 35% of the
above-ground biomass in the wetlands of the Qarlikturvik Valley.
From 1998 to 2007, years that we can compare with our two other
monitoring sites, the impact was slightly reduced, with 30% of
the above-ground biomass being grazed. The year during which the
greater impact was noticed is 1993, when geese removed 60% of
the above-ground biomass in the Qarlikturvik Valley. This year
also corresponds to a peak in the Bylot Island Greater
Snow Goose population.
In the main nesting colony, geese remove, on average, 29% of
the total above-ground biomass (data from 1998 to 2007). This
is slightly lower than what was observed in the Qarlikturvik Valley
for the same period. At the nesting colony, 2000 was a year with
particularly low grazing impact.
At Pointe Dufour, the average grazing impact, calculated from
1998 to 2007, is lower to that observed in the two other sites,
with 25% of the graminoid biomass removed by geese.