Satellite‐based evidence for shrub and graminoid tundra expansion in northern Quebec from 1986 to 2010

• Published in: Global Change Biology
• Main Authors: McManus, kelly M., Morton, Douglas C., Masek, Jeffrey G., Wang, Dongdong, Sexton, Joseph O., Nagol, Jyoteshwar R., Ropars, Pascale, Boudreau, Stéphane
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Tundra
• Online Access: http://dx.doi.org/10.1111/j.1365-2486.2012.02708.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2486.2012.02708.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2486.2012.02708.x

Abstract Global vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming. Local plot and air‐photo studies have documented recent changes in high‐latitude vegetation composition and structure, consistent with warming trends. To bridge these two scales of inference, we analyzed a 24‐year (1986–2010) L andsat time series in a latitudinal transect across the boreal forest‐tundra biome boundary in northern Q uebec province, C anada. This region has experienced rapid warming during both winter and summer months during the last 40 years. Using a per‐pixel (30 m) trend analysis, 30% of the observable (cloud‐free) land area experienced a significant ( P < 0.05) positive trend in the N ormalized D ifference V egetation I ndex ( NDVI ). However, greening trends were not evenly split among cover types. Low shrub and graminoid tundra contributed preferentially to the greening trend, while forested areas were less likely to show significant trends in NDVI . These trends reflect increasing leaf area, rather than an increase in growing season length, because L andsat data were restricted to peak‐summer conditions. The average NDVI trend (0.007 yr −1 ) corresponds to a leaf‐area index ( LAI ) increase of ~0.6 based on the regional relationship between LAI and NDVI from the M oderate R esolution S pectroradiometer. Across the entire transect, the area‐averaged LAI increase was ~0.2 during 1986–2010. A higher area‐averaged LAI change (~0.3) within the shrub‐tundra portion of the transect represents a 20–60% relative increase in LAI during the last two decades. Our L andsat‐based analysis subdivides the overall high‐latitude greening trend into changes in peak‐summer greenness by cover type. Different responses within and among shrub, graminoid, and tree‐dominated cover types in this study indicate important fine‐scale heterogeneity in vegetation growth. Although our findings are consistent with community shifts in low‐biomass vegetation types over multi‐decadal ...