Research Proposal
Photo taken along the Dalton Highway looking toward the Brook Range, 2011
Evaluating Shrub Expansion and its Impact on Surface Albedo During the Last Decade in the North Slope, Alaska
Over the last 30 years the Arctic has warmed about 2°C per decade (ACIA, 2004). This warming has produced a series of environmental changes (Hinzman et al., 2005) including a shift in land surface vegetation (Stow et al., 2004). Recent warming at northern high latitudes - amplified by a reduction in the extent of sea ice - is causing tundra permafrost to thaw, potentially allowing the release of large volumes of methane and carbon dioxide into the atmosphere. Higher concentrations of greenhouse gases have a positive feedback on the Earth’s surface temperate.
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​ Arctic vegetation is rapidly changing toward a more shrubbery tundra as evidenced by many lines of work as a result of polar amplification in the higher latitude (Stow et al., 2004; Hudson & Henry, 2009). Predictions for 2100 indicate that increase in biomass will cause a decrease in summer albedo and enlargement of the snow free period by ~50days (Euskirchen, 2009). These changes are important positive feedbacks to climate warming because more solar radiation is absorbed by the surface promoting warming of the ground (Chapin et al., 2000).
​Present studies on shrub expansion at this time are either limited in spatial scale (i.e., Tape et al., 2006), in temporal scales (i.e., Beck et al., 2011) or used vegetation indices, such as the NDVI, as proxy for plant growth (i.e., Myneni et al., 1997, Jia et al., 2003). However, NDVI maps derived from spaceborne remote sensing sensors do not adequately represent shrub cover characteristics across the arctic tundra biome (Selkowitz, 2010) because they frequently display nonlinear relationships with canopy attributes and should be used only as an estimate for canopy light absorption instead of as a proxy for features of canopy architecture (Rees et al., 1998).
An alternative approach for mapping fractional cover with high temporal resolution is by exploiting data from the MISR instrument using Bootstrap Forest model with robust calibration data. A similar method called has been recently used by Beck et al 2011 to estimate fractional cover in tundra using Landsat imagery with some success. However, due to the Landsat’s 16-day revisit cycle, they used imagery from three years to provide full, nearly cloud-free coverage of the North Slope of Alaska. With MISR, that issue is solved because it has high temporal resolution and its coarse moderate resolution is most suitable for large-scale mapping. On the other hand, mapping rapid changes in surface albedo can be achieved by using the MODIS surface albedo product which offers high temporal resolution, excellent for capturing rapid changes during the shoulder season when fast changes on snow cover happen (Wang et al., 2012). The aim is to generate yearly fractional cover maps to better understand the relationship between increase shrub cover and snow patterns which is an important component in large-scale climate processes.
Photo taken south of the Brook Range, interior Alaska 2011
ACIA. (2004). Arctic Climate Impact Assessment. Cambridge University Press, Cambridge.
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Beck P., Horning N., Goetz S., Loranty M., & Tape K. (2011). Shrub cover on the North Slope of Alaska: a circa 2000 baseline map. Arctic, Antarctica and Alpine Research. 43(3):355-363.
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Chapin F. S. III., Eugster W., McFadden J. P., Lynch A. H., Walter D. A. (2000a). Summer Differences among Arctic Ecosystems in Regional Climate Forcing. J. Climate, 13: 20022010.
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Euskirchen E. S., McGuire A. D., Chapin F. S. III, Yi S., & Thompson C. C. (2009). Changes in Vegetation in Northern Alaska under Scenarios of Climate Change, 2003-2100:
Implications for Climate Feedbacks. Ecological Applications, 19(4): 1022-1043.
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Hudson J. M. G., & Henry G. H. R. (2009). Increased Plant Biomass in a High Arctic Heath Community from 1981 to 2008. Ecology, 90(10): 2657-2663.
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Jia G., Epstein H., & Walker D. (2003). Greening of Arctic Alaska, 1981–2001. Geophysical Research Letters, Vol. 30 No. 20: 2067.
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Myneni R., Keeling C., Tucker C., Asrar G., & Nemaniet R. (1997). Increased Plant Growth in the Northern High Latitudes from 1981 to 1991. Nature, 38: 698–702.
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Rees, W.G., Golubeva, E.I., and Williams, M., (1998). Are vegetation indices useful in the. Arctic?, Polar Record, 34, 333–336.
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Selkowitz D. (2010). A Comparison of Multi-spectral, Multi-angular, and Multi-temporal Remote Sensing Datasets for Fractional Shrub Canopy Mapping in Arctic Alaska. Remote Sensing of Environment, 114: 1338–1352.
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Stow D., Hope A., McGuire D., McGuire D., Verbyla D., Gamon J., Huemrich F., …& Myneni R. (2004). Remote Sensing of Vegetation and Land-Cover Change in Arctic Tundra
Ecosystems. Remote Sensing of Environment, 89: 281–308.
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Tape K., Sturm M., & Racine C. (2006). The Evidence for Shrub Expansion in Northern Alaska and the Pan-Arctic. Global Change Biology, 12: 686-702.
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