 |
 |
 |
          |
 |
Index > Ecological Monitoring > Plant Monitoring > Productivity and Grazing Impacts |  |
 |
Animal Species | Plant Monitoring | Climate Impact on the Ecosystem | Carbon Cycle
plant monitoring
Wetlands
Introduction
Wetlands
As we mentioned, Bylot Island has habitats of rare plant productivity for an Arctic ecosystem and this exceptional productivity attracts and sustains tons of thousands of breeding migratory bird species, including the Greater Snow Goose.
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 and sedges.
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.
Results
Wetlands Productivity
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.
The 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 term average.
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.
