Lianas are abundant and influential in tropical forests but decline sharply in cooler regions. This pattern has been attributed to their hydraulic structure consisting of a few large vessels, which are vulnerable to freeze–thaw embolisms. Although this hypothesis carries significant implications under global warming, the actual hydraulic functioning of lianas in cooler regions remains poorly understood.

We examined vessel anatomy, seasonal patterns of stem hydraulic conductivity (K_s) and sap flux, and xylem pressure profiles in early spring for nine tree and four liana species in a cool-temperate deciduous forest. We hypothesised that lianas would possess larger vessels and experience a more pronounced decline in Ks during winter, resulting in stagnation of K_s and sap flux during part of the growing season.

 Based on their responses to freeze-induced hydraulic damage, species were classified into three categories: resistant (three tree species), refill using positive xylem pressure (four tree and two liana species), and reconstruct with newly produced vessels (two tree and two liana species).

 Compared with tree branches of similar diameter and age, liana branches had substantially wider vessels and, on average, ten times greater K_s, supporting six times greater leaf area. While they experienced a nearly complete loss of K_s during winter, refill species restored conductivity before budbreak and reconstruct species recovered later, similar to the pattern observed in trees. The seasonal sap flux patterns (i.e. the relative transpiration activity in spring, summer and autumn) were largely species-specific, with no consistent trend unique to lianas. The time course and magnitude of positive xylem pressure in refill lianas fell within the range observed in trees and were sufficient to transport water to the upper canopy.

Cool-temperate lianas maintained hydraulic function as effectively as trees due to shared recovery mechanisms following declines under subfreezing temperatures. Additional factors beyond vessel vulnerability to freeze-thaw embolism are therefore likely to contribute to the latitudinal distribution patterns of lianas. A more comprehensive understanding of these factors may be key to predicting future changes in the dominance and ecological influence of lianas in temperate forest dynamics.