Feasibility of hyperspectral vegetation indices for the detection of chlorophyll concentration in three high Arctic plants: Salix polaris, Bistorta vivipara, and Dryas octopetala

Remote sensing, which is based on a reflected electromagnetic spectrum, offers a wide range of research methods. It allows for the identification of plant properties, e.g., chlorophyll, but a registered signal not only comes from green parts but also from dry shoots, soil, and other objects located next to the plants. It is, thus, important to identify the most applicable remote-acquired indices for chlorophyll detection in polar regions, which play a primary role in global monitoring systems but consist of areas with high and low accessibility. This study focuses on an analysis of in situ-acquired hyperspectral properties, which was verified by simultaneously measuring the chlorophyll concentration in three representative arctic plant species, i.e., the prostrate deciduous shrub <em>Salix polaris</em>, the herb <em>Bistorta vivipara</em>, and the prostrate semievergreen shrub <em>Dryas octopetala</em>. This study was conducted at the high Arctic archipelago of Svalbard, Norway. Of the 23 analyzed candidate vegetation and chlorophyll indices, the following showed the best statistical correlations with the optical measurements of chlorophyll concentration: Vogelmann red edge index 1, 2, 3 (VOG 1, 2, 3), Zarco-Tejada and Miller index (ZMI), modified normalized difference vegetation index 705 (mNDVI 705), modified normalized difference index (mND), red edge normalized difference vegetation index (NDVI 705), and Gitelson and Merzlyak index 2 (GM 2). An assessment of the results from this analysis indicates that <em>S. polaris</em> and <em>B. vivipara</em> were in good health, while the health status of <em>D. octopetala</em> was reduced. This is consistent with other studies from the same area. There were also differences between study sites, probably as a result of local variation in environmental conditions. All these indices may be extracted from future satellite missions like EnMAP (Environmental Mapping and Analysis Program) and FLEX (Fluorescence Explorer), thus, enabling the efficient monitoring of vegetation condition in vast and inaccessible polar areas.

Constraints on dendrochronological dating of Salix polaris from central Spitsbergen ( Short communication )

Application of tundra shrubs in dendrochronological studies is recently increasing. However their growth rings are characterized by high irregularity which cause a com-mon tree-ring dating problems. The goal of the study is to demonstrate a dendro-chronological potential of common tundra species Salix polaris from central Spitsbergen (Ebbadalen, Petuniabukta) while (i) presenting its radial growth pattern and irregularities and (ii) discussing on its example a common problems of Arctic shrubs radial growth cross-dating. The results revealed that in average 25% of growth ring measured per single shrub was irregular and therefore might be problematic to detect and cross-date. It was found that even on a short distance (i.e., along a main root axis) cambial activity is not equal and missing and partially missing rings occurred alternately in a longitudinal profile. Common growth irregularities, such as missing and wedging rings, must be taken into account while measuring and cross-dating such a difficult dendrochrono-logical woody material as shown on the example of a Salix polaris dwarf shrub. The study revealed a high importance of serial sectioning and intra-plant cross-dating in dendrochronological studies of tundra shrubs.