Response of the two rare arable weed species Lithospermum arvense and Scandix pecten-veneris to climate change conditions

Rare weeds are currently under pressure due to intensifying arable management practices, and as a consequence of climate change, these practices will likely become even more intensive, together with a greater uniformity of land use. As a result, ecological stresses will increase for most species of rare weeds, in some cases leading to their further decline or even extinction. Moreover, climate change will alter the suitability of the environment for many plants, since average temperatures are predicted to increase and precipitation extremes to become more common. For most arable weed species it is unclear, whether the anticipated changes in environmental conditions are disadvantageous or beneficial. Little is known about specific biological responses of rare weeds to climate changes, and this study attempts to close some of these knowledge gaps. Here, the rare arable weed Lithospermum arvense and the endangered arable species Scandix pecten-veneris were investigated with regard to the effects of higher temperature and different crop densities on flowering time, shoot development, plant height, dry mass and seed production. Semi-field experiments were conducted with winter wheat crop for 3 years, involving 48 climate cages, in which every second was a variant of warmer temperature and contrasting crop density. We observed that S. pecten-veneris flowered earlier under warmer conditions and had fewer seeds and less biomass in the dense wheat crop compared to control conditions, while L. arvense grew taller, it produced fewer seeds in the high density crop. We suggest that such data concerning the biological responses of weeds can improve the precision of bioclimatic distribution models. Finally, we discuss strategies, such as relocation or non-intrusive management practices, for preventing further disappearances of rare arable weeds. Our results should be of considerable interest for the fields of plant ecology, biodiversity research and conservation.