Vegetation Greening Trends at Two Sites in the Canadian Arctic: 1984–2015

Paul Treitz,Rebecca Edwards

doi:10.1657/aaar0016-075

Abstract

ABSTRACTThis study examined vegetation greening at two arctic sites: the Apex River Watershed (ARW), Baffin Island, Nunavut (a Low Arctic site) and the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut (a High Arctic site). The vegetation at both study sites was characterized using a supervised land-cover classification approach using high spatial resolution satellite remote sensing data (i.e., IKONOS [4 m] and WorldView-2 [2 m]). Meanwhile, Normalized Difference Vegetation Index (NDVI) data spanning the past 30 years were derived from intermediate spatial resolution data (i.e., Landsat TM/ETM/OLI [30 m]). The land-cover classifications were used to partition the Landsat NDVI time series by vegetation type. Climate variables (i.e., temperature, precipitation, and growing season length [GSL]) were examined to explore potential relationships of NDVI to climate warming trends. The results of the land-cover classifications demonstrated inherent trends of vegetation types along elevation and moisture gradients. The NDVI time series for the CBAWO (1985–2015) demonstrated an overall significant increase in greening, specifically in the dry and mesic vegetation types. Conversely, similar greening (overall or by vegetation type) was not observed for the ARW (1984–2015). Based on climate data from the nearest permanent weather station (Mould Bay, Nunavut), the overall increase in NDVI at the CBAWO was largely attributed to a significant increase in July temperatures and GSL.

Highlights

Global air surface temperatures have increased over the past several decades with the most rapid warming occurring in the Arctic (ACIA, 2004; Barber et al, 2008; AMAP, 2011; IPCC, 2013)
Winter temperatures and snowmelt timing have been found to correlate with vegetation growth the following summer (Myers-Smith et al, 2011).The results reported here suggest that compared to the Apex River Watershed (ARW), there was proportionately more greening at the Cape Bounty Arctic Watershed Observatory (CBAWO), which can be attributed, in part, to higher summer temperatures (Fig. 6, part b) and an increased growing season length (GSL) (Fig. 7, part b)
The Normalized Difference Vegetation Index (NDVI) time series for both sites were coupled with high resolution land-cover classifications in order to identify specific vegetation types and quantify their response to climate

Summary

Introduction

Global air surface temperatures have increased over the past several decades with the most rapid warming occurring in the Arctic (ACIA, 2004; Barber et al, 2008; AMAP, 2011; IPCC, 2013). The satellite record has revealed that vegetation biomass and productivity in tundra ecosystems have already begun to change, resulting in a spatially variable trend of “Arctic greening” that is coincident with changes in surface temperatures (ACIA, 2004; Stow et al, 2004; Jia et al, 2009; Zeng et al, 2011; IPCC, 2013; Xu et al, 2013; Pearson et al, 2013; Fraser et al, 2011, 2014; Guay et al, 2014; Meyers-Smith et al, 2015; Moffat et al, 2016; Ju and Masek, 2016). Whether this is a temporary phenomenon, or an indication of a more systemic response to warming is yet to be determined (Phoenix and Bjerke, 2016)

Methods

Results

Discussion

Conclusion