| Summary: | Since the mid-1950s, studies have frequently been conducted on couplings between geometrid moth outbreaks and mountain birch, though not nearly as much focus has been on connections between geometrid moth outbreaks and ground cover. Previous studies have shown that major outbreaks of Epirrita autumnata occur in 9 – 10-year cycles (Karlsson et al., 2004). Sometimes also the Operophtera brumata are present in outbreaks in Abisko (Bylund, oral comment). Not until the larvae have finished feeding on the mountain birch, do they move on to the ground cover (Bylund, oral comment). Historically notorious outbreaks of geometrid moths occurred 1954 – 1955 (the most comprehensive outbreak on record), 1963, 1973 – 1974, 1984, 2003 – 2004 (with some registered repercussions in 2005) and 2012 – 2014. The study was aimed at finding methods to describe how geometrid moth larvae affect the mountain birch forest as an ecosystem. Like many previous studies, the study treated the regions around Abisko, Vadvetjåkka and Kopparåsen/Katterjåkk (northern Sweden), which all lie in the subalpine mountain birch belt. In accordance with the Swedish Environmental Protection Agency (Swe. Naturvårdsverket), mountain birch forests were defined as regions where the mountain birch constitutes at least 50% of the surface (Naturvårdsverket, 2012). The study made use of a combination of (i) low-resolution satellite data of vegetation indices (NDVI provided by MODIS), (ii) photographs (taken from both the air and the ground level) and (iii) interviews. The interviewed individuals were people which possess highly relevant information and which together contributed with a wide knowledge of moth outbreaks in the birch forests around Abisko. The study separated spring season NDVI values from summer (high) season NDVI values. For the high season, seasonal average NDVI values were calculated for each year by taking the mean of the four values provided by MODIS for every summer. In contrast to the treatment of the high season values, the annual spring ...
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