ABOUT THE STUDY
In a large-scale field experiment with a total of 30 stands, divided into 15 pairs of Lodgepole pine (Pinus contorta) and Swedish pine (Pinus sylvestris) in central and northern Sweden, the researchers investigated the effects of Lodgepole pine plantations on the abundance and activity of forest ants, the density and species richness of other ant species and the abundance of the beetle Pella humeralis, which specialises in eating ants.
The experimental plantations were established in the late 1960s by the Swedish forest company SCA. The different stands were planted in pairs on the same calcareous ridge and have been managed as normal production forests. Other self-seeded tree species have not been actively cleared.
In total, more than 40,000 ants were collected, from 11 different species, the most common of which was the northern wood ant. Fifty-seven ant mounds were recorded, of which 20 in Lodgepole pine forest and 37 in Swedish pine forest. Where there were more ants, there were also more beetles of the specialised ant predator Pella humeralis, suggesting that this species is also negatively affected by the Lodgepole pine.
A total of 159 trees were observed for one minute each, when all ants moving up or down the trunk in search of food were recorded. The results were striking: a total of 123 ants were observed, of which only 14 were in Contorta forest and 109 in the native Swedish pine forest.
The study was funded by the Carl Tryggers Foundation and Formas.