Autumn cold acclimation of shoots does not explain the northern distribution limit of three southern exotic tree species in Finland

Frost hardiness (FH) is one of the key traits that limits distribution tree species in north. Different and ecotypes respond differently to drivers frost hardening may therefore have different survival capacities, especially their northern range. Several southern such as pedunculate oak (Quercus robur L.), Norway maple (Acer platanoides mountain elm (Ulmus glabra Hudson) natural limit Southern Finland. Here, we examined whether insufficient autumn northwards these three species. To end, monitored phenological events exotic Central Finland, further north from range species, for sake comparison, native silver birch (Betula pendula Roth.). In all a timely growth cessation was observed. The water content stem decreased, its dry mass increased rapidly August before onset hardening, after which no major changes were observed two traits. early phase there differences leaf colouring between four values electrical impedance parameters changed during with clear turning point first night frosts at end September. Depending on phase, high temperature exotherm (HTE) -3 °C -10 °C, but HTE did not indicate hardening. started beginning September proceeded equal rates, more rapid later than other damaging assessed by controlled freezing tests became wider increasing FH. occurrence rate low (LTE) varied LTE around -35 last sampling December (no birch). We conclude took place manner so each, sufficient survive experimental site Further studies are needed examine also tolerate temporarily occurring extreme winter conditions temperatures below short-term variations spring.