| Summary: | The purpose of the study was to increase the understanding of the distribution of pine stem rust (Cronartium pini) in young pine (Pinus sylvestris) forests in the northern parts of Sweden. In addition, this study also investigates how the density of cow-wheat (Melampyrum spp.), altitude and proportion of deciduous trees in a stand affects the relative frequency of pine stem rust. The results showed a difference in the distribution of pine stem rust between investigated regions, with Norrbotten county having the largest occurrence with an average relative frequency of 6,9 % and Västernorrland/Jämtland county having the lowest with an average of 0,5 %. Furthermore, results showed that investigated areas with a high frequency of cow-wheat had the highest frequency of pine stem rust in almost all parts of data. The result is most likely due to cow-wheat being important host plants for pine stem rust. Weak correlations were found between altitude and pine stem rust as well as between proportion of deciduous trees and pine stem rust. The weak correlations indicates that there are more factors affecting the occurrence of pine stem rust. However, in following studies of collected data all investigated factors needs to be compared to determine their importance and how they interact with each other. Additionally, comparing the two variants of pine stem rust are essential to increase the understanding of their differences.
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