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The spatial relationships among vegetation phenology, plant community composition and environment at a High Arctic oasis Bean, David

Abstract

Environmental changes resulting from global warming are predicted to be most intense at high latitudes and this has considerable implications for the vegetation in the High Arctic. The relationships among plant community structure, diversity, phenology, and abiotic factors including snowmelt pattern, temperature, soil moisture and soil nutrients were studied at the Alexandra Fiord lowland (78° 53' N, 75° 55" W), a high arctic oasis on the east coast of Ellesmere Island. At each of 28 sampling points, vegetation was surveyed, soil was sampled, temperature was recorded by dataloggers and phenological observations were made on four dominant plant species throughout one growing season. Digital aerial photographs were used to study the pattern of snowmelt across the lowland. A geographic information system Was used to analyze the data from the discrete sampling points and relate them to the observed distribution of plant communities. Plant communities were analyzed using single linkage cluster analysis, principal components analysis and redundancy analysis including spatial information in the direct gradient analysis. Phenological development of Cassiope tetragona and Dryas integrifolia was strongly correlated to the temperature gradient across the lowland but Saxifraga oppositifolia and Salix arctica were not. The two former species flowered later in the season while the other two flowered shortly after snowmelt. The data were compared to an 8 year record of phenological observations at the site and Dryas was found to have a more pronounced response to temporal variability, whereas Cassiope had much more fixed timing for phenological development at a given place over time, while varying considerably across spatial gradients. Five major plant communities and two subtypes were defined. Moisture was found to be the most important environmental factor separating plant communities as is common these studies in the Arctic. Temperature was also an important factor in the indirect gradient analysis but this variable was highly spatially autocorrelated and much of the variation explained by temperature could be explained by spatial location information alone. The pattern of snowmelt did not vary at the same scale as the vegetation according to these results, and is thus not likely a major determinant of landscape-scale plant community distribution. The distribution seems more like a successional sequence resulting from differing times since the retreat of both Pleistocene and Little Ice Age glacier advances.

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