Winter conditions affect performance of garden lupine (Lupinus polyphyllus) and its impact on meadow vegetation during early stages of colonization

• Lupine affects the species composition of invaded site in early colonization stage • Snow poor winter conditions disadvantaged young lupines • Lupine neighbor affected leaf chlorophyll content two meadow species Mesocosms containing experimental meadow plant communities were subjected to differing winter conditions during two years by means of transfer to different overwintering locations. One is a mainland site where persistent snow cover commonly forms, protecting plants against freezing and fluctuating air temperatures. The other location is an off-coast site in the archipelago of SW Finland where the snow cover is ephemeral, and spring is early but cold. This site was chosen to approximately represent such winter conditions that are expected in mainland Finland as climate warming progresses. Invasion susceptibility was investigated by introducing an invasive legume Lupinus polyphyllus Lindl. (Fabaceae) into half of the mesocosms. Plant cover in summer was affected by the preceding winter conditions. Overwintering of juvenile lupines was less successful at the snow poor off-coast site compared to the snow rich mainland site in the first year reducing flowering and leaf production in the following summer. Judging by changes in cover, native meadow plants were generally resilient to snow poor winter conditions. Furthermore, the meadow plants were able to utilize an early and warm spring for abundant growth in the second year. Lupines suppressed the growth of three meadow species; Dianthus deltoides and Rumex acetosella showed marked decreases in cover during the lupines’ early colonization stages, and Trifolium arvense almost disappeared from lupine-inhabited mesocosms. Antennaria dioica , may have benefitted from the nitrogen fixing lupine and showed persistent increases in leaf chlorophyll content. The results show that the lupine causes changes in meadow vegetation already in early phases of colonization.