Evaluating six crop mixes used for game fields in southwest Sweden : biomass production, fallow deer preference and species diversity

Abstract: Game fields are one way to divert animals away from sensitive areas, create shelter and forage, and also to increase the biological diversity. In this study I investigated how the plant composition in six different crop mixes used for game fields affected the biomass production, biomass consumption and biological diversity at the Koberg estate in southwestern Sweden. Six experimental fields were used and each field contained six plots, approximately 1500 m2 each, that was sown with a different crop mix. The crop mixes ranged from a pure grass mix (A), 70 % grass and 30 % leguminous plants (B), 53 % grass, 21 % leguminous plants and 26 % other herbs (C), 100 % leguminous plants (D) to the most complex mixes constituting of 91 % leguminous plants and 9 % other herbs (E) and 87 % leguminous plants and 13 % other herbs (F). The fields were cut weekly during the summer in 2010, to estimate weekly biomass production. Also a seasonal biomass production was measured inside stationary exclosures, before and after harvest. Exclosures and GPS marked fallow deer (Dama dama) were used to estimate biomass consumption and preference. To estimate species diversity I used pitfall traps, beating nets and transects to collect arthropods. The seasonal biomass production without grazing showed that crop mix B, C, D, F produced better than A and E during summer 2010. There was no significant difference between the different crop mixes in weekly biomass production, however a significant difference was found between experimental fields. No significant differences were found in weekly biomass consumption, but crop mix A, D and F had been consumed the most. Two independent measures of the relative use of the six crop mixes showed a similar pattern (GPS locations and relative biomass loss) as crop mix A, E and F was used or grazed more than expected and crop mix B and C was avoided. Simpson´s and Shannon´s diversity index both indicated that crop mix D was the most diverse for carabids (Carabidae) and mirids (Hemiptera: Miridae), while crop mix E was the most diverse for spiders (Araneae). Sequential counting index showed that crop mix D was the most diverse for true flies (Diptera). However, I found no significant difference between the different crop mixes regarding abundances of bumblebees (Apidae) and butterflies (Lepidoptera).