Invasive earthworms influence on boreal forest plant communities both below- and aboveground

Sammanfattning

Invasive earthworms are changing ecosystems around the world. Through bioturbation and feeding behaviours non-native earthworms reconstruct soil structure, change its chemical properties and causes shifts in plant community compositions. The Scandinavian boreal forests have been free from burrowing earthworm since the last ice age, but, through anthropogenic activities, invasive earthworms are now spreading across the landscape. Still, few studies have explored the consequences of earthworm invasion in boreal forests. This report aims to study the effects of earthworm invasion on boreal forest plant communities above- and belowground. I have analysed aboveground vegetation composition and fine roots from ingrowth mesh bag from a mesocosm experiment where soil monoliths from twelve different boreal forests were treated with one of four different treatments, control low-and high densities of living earthworms and one treatment of dead earthworms. Fine root production, specific root length, root dry matter content, specific surface area and vegetation cover of different functional groups were analysed using linear mixed-effects models. No of the earthworm treatments differed from the control but the treatments differed from each other and a significant interaction between vegetation cover and fine root production where fine root production did not increase as much with vegetation cover in the high-density earthworm treatment than in the other treatments. The other roots traits showed no response to earthworm presence, and there were fewer graminoids in the high-density worm treatment than in the low- and dead-worm treatments but not compared to the control. As such, the results suggest complex, non-linear interactions not always in line with previous studies from other biomes, which shows that more information is needed on earthworm effects in boreal forests.