Bachelor's presentation, biology

Frida Gustafsson, 15 hp degree work:
Trends in birch seed abundance and its relation to larval abundance and temperature: a ten-year study from Swedish Lapland 

Boreal forest is the world’s largest terrestrial biome. Being one of the most ubiquitous and cold-tolerant tree species in Sweden, the mountain birch forms a unique deciduous treeline and marks the forest-tundra ecotone. Its reproduction and ability to spread is therefore important from both a societal and ecological perspective, locally as well as globally. Folivorous larvae reach outbreak levels in arctic and alpine areas approximately every 9-10 years and can severely defoliate birch trees. Cold winters kill the eggs of the folivorous insects. Global warming and changed interspecific interactions possibly present new challenges for mountain birch growth and reproductive success. The aim of this study was to investigate the trends in mountain birch seed abundance and how seed abundance is related to temperature and abundance of folivorous larvae. Further the aim was to investigate the effects of winter temperature on larval abundance. Seed rain was collected over a time period of ten years in Abisko by using seed traps set out from August to June. The seeds were manually sorted, and mountain birch seeds were counted. General linear models with Poisson distribution were made, using R, to investigate the significance and relationships between seed abundance and the drivers temperature, larval abundance and year. Models for larval abundance, with the drivers temperature and year, were also made. The results showed that seed abundance is neither increasing nor decreasing and that summer temperature and larval abundance do not significantly affect seed abundance. Contrarily, larval abundance increased both over time and with increasing winter temperature, possibly indicating that larval abundance and distribution will increase with the increasingly warmer climate. Yet whether this is an actual upgoing trend or if it is caused by the moth population cyclicity is unclear and must be studied for longer than ten years.