Chao Liu
Postdoctoral fellow
Department of Phytology
Laval University

Supervised by:

Line Rochefort (Regular member)

Research project description

Evaluation of the effect of global warming and Snow Geese herbivory on the structuration of bryophyte communities in the Canadian High Arctic

Introduction: The Greater Snow Goose is a medium-sized herbivore whose population size has increased markedly in the second half of the last century, mostly because of intensified foraging on agricultural lands in its wintering habitat. This population expansion has increased foraging pressure on their breeding habitat located in the Arctic, a biome apparently prone to strong herbivore control. In polygon fens of the Arctic, although geese do not feed on bryophytes, they disturb physically the moss carpet during the process of feeding on graminoid rhizomes, a foraging mode called grubbing. In this project, we explore how goose grazing influences the composition of bryophytes in arctic wetlands. Objectives: Bryophytes comprise an average of 30% of the vegetation cover and have a high species diversity across a broad range of tundra types, and their production accounts for a large proportion of net primary production in resource-limited regions. Despite the relative importance of bryophytes in the Arctic and Subarctic, few studies of herbivores on bryophytes are available for these regions. The aims of this project are: i) by investigating the composition of moss communities, we explore the effect of goose grazing on the species diversity of moss communities; ii) by monitoring the species diversity of moss communities at different spatial scales, we explore the effect of goose grazing on the slope of the species–area power function. Study sites: Located on northern Baffin Island in Nunavut, the 1600 km2 southwestern plain of Bylot Island (73°N, 80°W) .The average summer temperature is 4.5 °C and -32.8 °C in winter. The temperature of the region warmed by an average of 2.8 °C in spring and summer and 4.3 °C in autumn between 1976 and 2011. Snow cover is present from October to early June. From 1995 to 2019, the average amount of rain between June 1st to August 17th is 77.5 mm. Material and methods: Early during the 1994 growing season, 17 goose exclosures (4 x 4 m) made of 2.5-cm mesh chicken wire and covered with light nylon netting were set in the central area of as many polygon fens to initiate a study on the impact of snow goose grazing on its preferential food plants (essentially graminoid plants, see Gauthier et al. 2004). Exclosures were randomly located within 3 km from our main camp in one of the largest concentration of polygon fens in the island. The seven exclosures were surveyed 5 years and 11 years after they were erected. The experimental design is a complete random block with replication and measurements repeated in time. We surveyed the presence and absence of all species in each of 25 cells (2 x 2 cm) in a quadrat (10 x 10 cm) and sampled five quadrats inside and five quadrats outside the exclosures at both sampling periods. Expected results: Species diversity is much lower in goose exclosures treatments than outside the exclosures treatments. The slope of the species–area power function is much lower in goose exclosures treatments than outside the exclosures treatments (proving that snow geese is helpful to defuse the gametophyte of bryophytes). Positive interspecific spatial association is found in goose non-exclosure treatments. At small scale, interspecific spatial association is high and mainly negative because of competition among species. With the increase of scale, interspecific spatial association and the intensity of interspecific competition decreased, which could improve the survival conditions of the weak species. Thus, the species richness will increase.

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