A method using indicator plants to map local climatic variation in the Kangerlussuaq/Scoresby Sund area, East Greenland

Abstract Aim To describe a method for mapping local climatic variation using plants as temperature indicators. Location The study area is situated on the northern side near the mouth of the fiord Kangerlussuaq/Scoresby Sund, East Greenland (70–71°N). The study area consists of three subareas, divided into 136 1 × 1 km study units. It was selected because of its very strong climatic gradient as shown by data from four meteorological stations in the area, with mean July temperatures ranging from 2.7 to 9.3 °C. Methods The method is based on the fact that most vascular plant species occurring in the Arctic have circumpolar distribution patterns obviously limited by temperatures to a varying extent. By comparing the circumpolar distribution maps with summer temperatures, species are grouped according to minimum temperature demands and assigned indicator values. In the field, frequency and abundance of all indicator species and the occurrence of habitats are recorded in all study units. Indicator values and abundance data are entered into a formula of Index of Thermophily, and the resulting values are modified according to deviating habitat diversity and cover of unproductive areas. Index values are supposed to reflect local climatic conditions, and the results are tested by comparing with temperatures measured in the field. Results A total of 147 taxa, 139 of these being vascular plants, were defined in six categories of temperature indicators. The Index of Thermophily values calculated for the 136 study units show a complex pattern and a strong positive relationship with the temperatures measured during 1991 and 1993, with r 2 values of 0.82 and 0.92, respectively. The unmodified Index version gave slightly lower correlations. A very strong gradient is demonstrated from the extremely cold coastal community of Uunarteq/Kap Tobin to more protected sites only 20 km inland, where a similar climate is found at 1100 m altitude. Favourable slopes also produce a favourable climate at altitudes of 700 m. The warmest sites are the south‐facing slopes of five deep river gorges, all with similar Index values and the occurrence of Salix shrubs. The results are used to make a local bioclimatic map, including allowances for topographic features and detailed knowledge on the occurrence of concentrations of thermophilous plants. Here fourteen climate classes are mapped in detail, and these mapping units can be correlated to four of five subzones present in the Arctic on a circumpolar scale. The correlation with these subzones shows that the study area has the strongest horizontal climate gradient recorded from the Arctic. Main conclusions The strong positive correlation between the calculated Index of Thermophily values and measured temperatures indicate that the present method is successful in mapping local bioclimatic heterogeneity in the Arctic.