Vole–vegetation interactions in an experimental, enemy free taiga floor system

Authors

  • Üllar Rammul,

  • Tarja Oksanen,

  • Lauri Oksanen,

  • Jouko Lehtelä,

  • Risto Virtanen,

  • Johan Olofsson,

  • Joachim Strengbom,

  • Ivi Rammul,

  • Lars Ericson


Ü. Rammul, J. Lehtelä, R. Virtanen, Dept of Biology, Univ. of Oulu, Box 3000, FI-900 14 Univ. of Oulu, Finland. Present address for ÜR: Dept of Gene Technology, Tallinn Univ. of Technology, Akadeemia tee 15, EE-12618, Tallinn, Estonia. – T. Oksanen (tarja.oksanen@emg.umu.se), L. Oksanen, J. Olofsson, J. Strengbom and L. Ericson, Dept of Ecology and Environmental Science, Umeå Univ., SE-901 87 Umeå, Sweden. Present address for LO: Dept of Biology, Univ. of Turku, FI-200 14 Turku, Finland. Present address for JS: Evolutionary Biology Centre, Plant Ecology, Uppsala Univ., Villavägen 14, SE-752 36 Uppsala, Sweden. – I. Rammul, Pirita Business Highschool, Metsavahi tee 19, EE-11911 Tallinn, Estonia.

Abstract

Vole–vegetation interactions in a predation-free taiga environment of northern Fennoscandia were studied by transferring vegetation from natural Microtus habitats into a greenhouse, where three habitat islands of about 30 m2 were created. The ‘islands’ were subjected to simulated summer conditions and a paired female field vole, Microtusagrestis, was introduced to each ‘island’. The development of the female and her young was followed by recurrent live trapping. The development of the vegetation was followed by recurrent marking and censusing of plant shoots at intervals of five days. In the next growing season, two ‘islands’ were subjected to a new grazing treatment to study the impacts of repeated grazing on the vegetation and on the growth and reproduction of voles. Plant biomasses were harvested at the end of each trial. In all trials, the biomasses of graminoids and non-toxic herbs other than ferns, fireweeds and rosaceous plants were profoundly decimated. Even the biomass of a toxic herb Aconitum lycoctonum decreased largely at pace with the palatable herbs. The least preferred plant categories maintained their biomasses at control levels. Their neutral collective response was created by opposite species-level trends. Species typical for moist and nutrient-rich forests suffered from vole grazing, whereas the biomass of species adapted to disturbed habitats increased.

In spite of the dramatic changes in the vegetation, the introduced female voles survived throughout the trials and reproduced normally. The young of their first litters survived well and reached the final weights typical for individuals starting to winter as immatures. We conclude that most of the plant biomass found on productive boreal forest floors is potential food for field voles and remains palatable for them even when subjected to recurrent, severe grazing. If nothing else than summer resources were limiting the growth of the field vole populations, the plants currently dominating moist and nutrient-rich taiga floors could not survive in this habitat.

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