The ability of plants to tolerate freezing limits their geographical distribution. Therefore, winter warming may shift a species’ occurrence northwards and/or to higher altitudes. The hemiparasitic Viscum album album (European mistletoe) has a more northern geographic distribution than the pine mistletoe (V. album austriacum) but host trees of both subspecies (deciduous trees and Scots pine, respectively) are abundant up to the arctic circle. We revealed that seeds of V. a. album tolerate lower temperatures than seeds of V. a. austriacum. The temperature at which 50% of seeds lost their ability to germinate (LT50) was -15◦C in V. a. austriacum and between -15◦C and -19◦C in V. a. album. The freezing tolerance of mistletoe seeds is relatively well coupled with the winter climate at the edge of their current geographic distribution. Therefore, the warming of winters may eliminate the abiotic barrier limiting mistletoes’ expansion, opening a window of opportunity for these parasites to increase their abundance and shift their distribution range towards higher latitudes and altitudes. This, in turn, may cause economic losses in forestry due to substantial reduction in tree growth.
The article was published owing to cooperation of researchers from Poland, Finland, Sweden, Spain and Switzerland in the framework of the International Centre for Research on Forest Ecosystems: Tikkanen O-P. et al. 2021. Freezing tolerance of seeds can explain differences in the distribution of two widespread mistletoe subspecies in Europe. Forest Ecology and Management, 482: 118806. DOI: 10.1016/j.foreco.2020.118806