Laboratory and Field Assessment of the Frost Resistance of Sosnowsky’s Hogweed

The frost resistance of Sosnowsky’s hogweed plants ( Heracleum sosnowsky Manden.) has been evaluated under laboratory and field conditions. The death of seedlings and adult plants observed within a temperature range from –6 to –12°C indicates low frost tolerance of the species. A snow cover provides a stable soil temperature (no less than –3°С) at the depth of renewal bud location and, therefore, provides the sustainability of meristematic potential in cenopopulations of H. sosnowsky. A shifting of freezing temperature for a H. sosnowsky meristem from –12°С (autumn) to –5 to –7°С (spring) is probably caused by the lack of a true dormancy stage and by changes in the content of cryoprotectors. Plant seeds also demonstrate reduced frost resistance after stratification (overwintering) and increased tissue water content. Field studies were carried out with assistance of volunteers within the framework of the “Moroz” (“Frost”) project arranged within the borders of the invasion habitat of the species in European Russia and based on the principles of citizen science. The results of the study show that the destruction of Sosnowsky’s hogweed plants after the snow cover removal depends only on weather conditions. Thus, elimination of H. sosnovsky stands by freezing can be recommended only for regions where average long-term minimum temperatures in January and February do not exceed –25°C; this method can be relevant for territories where the use of chemical herbicides is limited or prohibited.