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Remote Sens. 2018, 10(11), 1686; https://doi.org/10.3390/rs10111686

Vegetation Indices Do Not Capture Forest Cover Variation in Upland Siberian Larch Forests

1
Department of Geography, Colgate University, Hamilton, NY 13346, USA
2
Northeast Science Station, Pacific Institute for Geography, Far East Branch, Russian Academy of Sciences, Cherskiy 678830, Russia
3
Department of Forestry, Forest and Wildlife Research Center, Mississippi State University, Starkville, MS 39759, USA
4
Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ 86011, USA
5
Woods Hole Research Center, Falmouth, MA 02540, USA
*
Author to whom correspondence should be addressed.
Received: 21 September 2018 / Revised: 22 October 2018 / Accepted: 23 October 2018 / Published: 25 October 2018
(This article belongs to the Special Issue Optical Remote Sensing of Boreal Forests)
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Abstract

Boreal forests are changing in response to climate, with potentially important feedbacks to regional and global climate through altered carbon cycle and albedo dynamics. These feedback processes will be affected by vegetation changes, and feedback strengths will largely rely on the spatial extent and timing of vegetation change. Satellite remote sensing is widely used to monitor vegetation dynamics, and vegetation indices (VIs) are frequently used to characterize spatial and temporal trends in vegetation productivity. In this study we combine field observations of larch forest cover across a 25 km2 upland landscape in northeastern Siberia with high-resolution satellite observations to determine how the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) are related to forest cover. Across 46 forest stands ranging from 0% to 90% larch canopy cover, we find either no change, or declines in NDVI and EVI derived from PlanetScope CubeSat and Landsat data with increasing forest cover. In conjunction with field observations of NDVI, these results indicate that understory vegetation likely exerts a strong influence on vegetation indices in these ecosystems. This suggests that positive decadal trends in NDVI in Siberian larch forests may correspond primarily to increases in understory productivity, or even to declines in forest cover. Consequently, positive NDVI trends may be associated with declines in terrestrial carbon storage and increases in albedo, rather than increases in carbon storage and decreases in albedo that are commonly assumed. Moreover, it is also likely that important ecological changes such as large changes in forest density or variable forest regrowth after fire are not captured by long-term NDVI trends. View Full-Text
Keywords: boreal forest; NDVI; phenology; greening; Arctic; Siberia; larch; CubeSat boreal forest; NDVI; phenology; greening; Arctic; Siberia; larch; CubeSat
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Loranty, M.M.; Davydov, S.P.; Kropp, H.; Alexander, H.D.; Mack, M.C.; Natali, S.M.; Zimov, N.S. Vegetation Indices Do Not Capture Forest Cover Variation in Upland Siberian Larch Forests. Remote Sens. 2018, 10, 1686.

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