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Satellite-Based Evidence for Shrub and Graminoid Tundra Expansion in Northern Quebec from 1986-2010Global 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) Landsat time series in a latitudinal transect across the boreal forest-tundra biome boundary in northern Quebec province, Canada. This region has experienced rapid warming during both winter and summer months during the last forty 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 Normalized Difference Vegetation Index (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 Landsat data were restricted to peak-summer conditions. The average NDVI trend (0.007/yr) corresponds to a leaf-area index (LAI) increase of ~0.6 based on the regional relationship between LAI and NDVI from the Moderate Resolution Spectroradiometer (MODIS). 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 Landsat-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 time scales, the response in tundra and forest ecosystems to recent warming was not uniform.
Document ID
20120010311
Document Type
Preprint (Draft being sent to journal)
Authors
McManus, K. M. (Stanford Univ. Stanford, CA, United States)
Morton, D. C. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Masek, J. G. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Wang, D. (Maryland Univ. College Park, MD, United States)
Sexton, J. O. (Maryland Univ. College Park, MD, United States)
Nagol, J. (Maryland Univ. College Park, MD, United States)
Ropars, P. (Laval Univ. Sainte-Foye, Quebec, Canada)
Boudreau, S. (Laval Univ. Sainte-Foye, Quebec, Canada)
Date Acquired
August 26, 2013
Publication Date
January 1, 2012
Subject Category
Earth Resources and Remote Sensing
Report/Patent Number
GSFC.JA.6432.2012
GSFC.JA.00241.2012
Distribution Limits
Public
Copyright
Public Use Permitted.

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