Changes in species abundance after seven years of elevated atmospheric CO 2 and warming in a Subarctic birch forest understorey, as modified by rodent and moth outbreaks

• Published in: PeerJ
• Main Authors: Svensson, Brita M., Carlsson, Bengt Å., Melillo, Jerry M.
• Other Authors: Swedish Environmental Protection Agency
• Format: Article in Journal/Newspaper
• Language: English
• Published: PeerJ 2018
• Subjects: General Agricultural and Biological Sciences; General Biochemistry, Genetics and Molecular Biology; General Medicine; General Neuroscience; Empetrum nigrum; Subarctic
• Online Access: http://dx.doi.org/10.7717/peerj.4843; https://peerj.com/articles/4843.pdf; https://peerj.com/articles/4843.xml; https://peerj.com/articles/4843.html

A seven-year long, two-factorial experiment using elevated temperatures (5 °C) and CO 2 (concentration doubled compared to ambient conditions) designed to test the effects of global climate change on plant community composition was set up in a Subarctic ecosystem in northernmost Sweden. Using point-frequency analyses in permanent plots, an increased abundance of the deciduous Vaccinium myrtillus , the evergreens V. vitis-idaea and Empetrum nigrum ssp. hermaphroditum and the grass Avenella flexuosa was found in plots with elevated temperatures. We also observed a possibly transient community shift in the warmed plots, from the vegetation being dominated by the deciduous V. myrtillus to the evergreen V. vitis-idaea . This happened as a combined effect of V. myrtillus being heavily grazed during two events of herbivore attack—one vole outbreak ( Clethrionomys rufocanus ) followed by a more severe moth ( Epirrita autumnata ) outbreak that lasted for two growing seasons—producing a window of opportunity for V. vitis-idaea to utilize the extra light available as the abundance of V. myrtillus decreased, while at the same time benefitting from the increased growth in the warmed plots . Even though the effect of the herbivore attacks did not differ between treatments they may have obscured any additional treatment effects. This long-term study highlights that also the effects of stochastic herbivory events need to be accounted for when predicting future plant community changes.