| Summary: | The purpose of the present study was to demonstrate possible effects on Collembola populations by changes in tree composition in natural birch forest in coastal North Norway. In the study area (Dønnes, Nordland County) parts of the natural mixed birch forest has been replanted with Norway spruce and Sitka spruce. Soil samples were collected in June and October 2004. A total of 52 species of Collembola were found (36 in birch, 32 Sitka, 34 Norway spruce). Eighteen species were common to all three sites, while birch had 12 unique species. Nine species from the coniferous plantations were not seen in birch, while Norway spruce and Sitka had only minor differences. The most abundant species were Mesaphorura macrochaeta, Isotomiella minor, Parisotoma notabilis and Megalothorax miniumus which made up 55% of all individuals found. Total abundance averaged on 91,000 (Sitka), 53,000 (Norway spruce) and 32,000 (birch) inds./m², with spring densities 40-80% higher than in autumn. The planting of Sitka/Norway spruce changed species composition but gave no significant reduction in species number, while population densities increased considerably.
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