Intraspecific Differences in Spectral Reflectance Curves as Indicators of Reduced Vitality in High-Arctic Plants

Bogdan Zagajewski,Andrzej Kłos,Samantha Lavender,Edwin Raczko,Hans Tømmervik,Dariusz Ziółkowski,Anna Jarocińska,Zbigniew Bochenek,Jarle Bjerke

doi:10.3390/rs9121289

Abstract

Remote sensing is a suitable candidate for monitoring rapid changes in Polar regions, offering high-resolution spectral, spatial and radiometric data. This paper focuses on the spectral properties of dominant plant species acquired during the first week of August 2015. Twenty-eight plots were selected, which could easily be identified in the field as well as on RapidEye satellite imagery. Spectral measurements of individual species were acquired, and heavy metal contamination stress factors were measured contemporaneously. As a result, a unique spectral library of dominant plant species, heavy metal concentrations and damage ratios were achieved with an indication that species-specific changes due to environmental conditions can best be differentiated in the 1401–2400 nm spectral region. Two key arctic tundra species, Cassiope tetragona and Dryas octopetala, exhibited significant differences in this spectral region that were linked to a changing health status. Relationships between field and satellite measurements were comparable, e.g., the Red Edge Normalized Difference Vegetation Index (RENDVI) showed a strong and significant relationship (R2 = 0.82; p = 0.036) for the species Dryas octopetala. Cadmium and Lead were below detection levels while manganese, copper and zinc acquired near Longyearbyen were at concentrations comparable to other places in Svalbard. There were high levels of nickel near Longyearbyen (0.014 mg/g), while it was low (0.004 mg/g) elsewhere.

Highlights

Arctic temperatures have increased, stimulating plant growth; a trend widely referred to as “the greening of the Arctic” [1,2,3]
Four different species were analyzed within seven measurement sites on Svalbard and the study verified that, using remote sensing methods and statistical analyses, polar plant species can be distinguished on the basis of their spectral properties
The spectral ranges were identified through statistical analysis of species’ spectral reflectance curves acquired for different measurement areas. Such information was complemented by remote sensing vegetation indices showing that all index values were in optimal ranges; according to the literature

Summary

Introduction

Arctic temperatures have increased, stimulating plant growth; a trend widely referred to as “the greening of the Arctic” [1,2,3]. Many northern latitudes have experienced suppressed growth known as browning. Summer droughts and wildfires are the main drivers of this browning trend [4,5]. In maritime regions other climatic and biotic drivers stress vegetation, e.g., frost drought [6] and ice-induced anoxia (plant damage following encasement in ground-ice). Plant damage from a changing winter climate is increasing in frequency [7,8], as winters are warming more than summers [9]. Environmental pollution is affecting plant vitality in northern ecosystems [10,11,12], which may make plants more vulnerable to climatic change

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