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TitleWarming-induced shrub expansion and lichen decline in the western Canadian Arctic
AuthorFraser, R H; Lantz, T C; Olthof, I; Kokelj, S V; Sims, R A
SourceEcosystems vol. 17, no. 7, 2014 p. 1151-1168,
Alt SeriesEarth Sciences Sector, Contribution Series 20130344
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
AreaTuktoyaktuk Coastal Plain
Lat/Long WENS-134.5000 -128.5000 70.2500 68.7500
Subjectsenvironmental geology; Nature and Environment; LANDSAT imagery; remote sensing; vegetation; permafrost; climate, arctic; climate; climatic fluctuations
ProgramRemote Sensing Science, Methodology
Released2014 07 16
AbstractStrong evidence for a pan-Arctic expansion of upright shrubs comes from analysis of satellite imagery, historical photographs, vegetation plots, and growth rings. However, there are still uncertainties related to local-scale patterns of shrub growth, resulting interactions among vegetation functional groups, and the relative roles of disturbance and climate as drivers of observed change. Here, we present evidence that widespread and rapid shrub expansion and lichen declines over a 15,000 km2 area of the western Canadian Arctic have been driven by regional increases in temperature. Using 30 m resolution Landsat satellite imagery and high resolution repeat color-infrared aerial photographs, we show that 85% of the land surface has a positive 1985–2011 trend (P < 0.05) in NDVI, making this one of the most intensely greening regions in the Arctic. Strong positive trends (>0.03 NDVI/decade) occurred consistently across all landscape positions and most vegetation types. Comparison of 208, 1:2,000 scale vertical air photo pairs from 1980 and 2013 clearly shows that this greening was driven by increased canopy cover of erect dwarf and tall shrubs, with declines in terricolous lichen cover. Disturbances caused by wildfires, exploratory gas wells, and drained lakes all produced
strong, yet localized increases in NDVI due to shrub growth. Our analysis also shows that a 4\'02C winter temperature increase over the past 30 years, leading to warmer soils and enhanced nutrient mineralization provides the best explanation for observed vegetation change. These observations thus provide early corroboration for modeling studies predicting large-scale vegetation shifts in low-Arctic ecosystems from climate change.
Summary(Plain Language Summary, not published)
Several recent studies have presented evidence of shrub expansion in the low-Arctic. However, there are still uncertainties regarding the extent of these changes and the plant types involved. For example, some authors have suggested that shrub expansion may have caused declines in lichens important for caribou forage. Our study presents evidence of widespread shrub expansion and lichen declines over a 15000 km2 area within western NWT using satellite imagery from 1985-2011 and high resolution vertical aerial photographs from 1980 and 2013. Our analysis shows that the most likely driver for the majority of shrub changes is a 4°C winter temperature increase over the past 30 years, leading to warmer soils and enhanced supply of growth-limiting nutrients. Natural and human disturbances also stimulated increases in shrub cover, but these effects were limited spatially. Our observations are consistent with warming experiments showing reductions in lichen cover from shrub growth, and modeling studies predicting large-scale vegetation shifts in the low-Arctic from climate change.