Abstract: Spatial and Temporal Patterns of Net Carbon Exchange in the Polar Semi-Desert Vegetation Community on Melville Island, NU (2015 Joint Assembly)

Spatial and Temporal Patterns of Net Carbon Exchange in the Polar Semi-Desert Vegetation Community on Melville Island, NU

Emma Buckley¹, Neal A Scott¹ and Paul Treitz², (1)Queen's University, Kingston, ON, Canada, (2)Queen's University, Geography and Planning, Kingston, ON, Canada

Contact First Author: Emma Buckley; emma.buckley@queensu.ca

Previously Published Material: Preliminary results presented as a poster at the 2014 Arctic Change conference.

Abstract ID#: 35068

English Abstract:

While studies across latitudinal gradients in mesic tundra have shown decreasing levels of net ecosystem exchange (NEE) of carbon dioxide at more northern sites, little work has explored the factors regulating NEE in the polar semi desert, a vegetation community which is widely distributed across the High Arctic.

In 2013, we deployed eight ADC Automated Carbon Exchange (ACE) systems to quantify the contribution of the polar semi-desert plant community to the landscape-scale NEE. As polar semi-desert plant cover varies at relatively small spatial scales, the chambers were distributed between vegetated areas (18-51% cover) and bare soil. Measurements were made every 30 minutes from late May to late July. Air temperature, soil temperature, and soil moisture measurements were collected in conjunction with NEE readings. In July 2013, Normalized Difference Vegetation Index (NDVI) data were collected to quantify variability in vegetation cover within the polar semi-desert. NDVI varied from -0.12 to 0.31, with the highest values occurring at vegetated sites and low values occurring on bare soil. Percent vegetation cover and NDVI correlated well at peak biomass (R² = 0.96).

NEE is driven by variability in several biophysical factors, and the factor that best predicts NEE varies throughout the season. In the early season, respiration drives NEE, and air temperature is the strongest predictor (R² = 0.23 to 0.55). During the warmer part of the season, photosynthesis is the dominant component of NEE, and photosynthetically active radiation (PAR) becomes the best predictor. Our results suggest a threshold temperature above which photosynthesis dominates NEE in polar semi-desert plant communities. Longer growing seasons, if associated with higher temperatures, would enhance NEE. NEE correlated positively with vegetation cover (R² = 0.96) later in the season. These relationships may be useful for quantifying NEE in polar semi-deserts using remotely-sensed data.

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