This report provides a brief review of key findings related to frost resistance in alpine woody plant species, summarizes data on their frost resistance, highlights the importance of freeze avoidance mechanisms, and indicates areas of future research. Freezing temperatures are possible throughout the whole growing period in the alpine life zone. Frost severity, comprised of both intensity and duration, becomes greater with increasing elevation and, there is also a greater probability, that small statured woody plants, may be insulated by snow cover. Several frost survival mechanisms have evolved in woody alpine plants in response to these environmental conditions. Examples of tolerance to extracellular freezing and freeze dehydration, life cycles that allow species to escape frost, and freeze avoidance mechanisms can all be found. Despite their specific adaption to the alpine environment, frost damage can occur in spring, while all alpine woody plants have a low risk of frost damage in winter. Experimental evidence indicates that premature deacclimation in Pinus cembra in the spring, and a limited ability of many species of alpine woody shrubs to rapidly reacclimate when they lose snow cover, resulting in reduced levels of frost resistance in the spring, may be particularly critical under the projected changes in climate. In this review, frost resistance and specific frost survival mechanisms of different organs (leaves, stems, vegetative and reproductive over-wintering buds, flowers and fruits) and tissues are compared. The seasonal dynamics of frost resistance of leaves of trees, as opposed to woody shrubs, is also discussed. The ability of some tissues and organs to avoid freezing by supercooling, as visualized by high resolution infrared thermography, are also provided. Collectively, the report provides a review of the complex and diverse ways that woody plants survive in the frost dominated environment of the alpine life zone.

We studied ice propagation in stems and leaves of various angiosperm deciduous and evergreen trees and shrubs and gymnosperms by differential thermal analysis (DTA) of thermal images captured with a digital infrared camera. This so-called infrared DTA (IDTA) technique should elucidate the smallest freezing exotherms in plant tissues. After intrinsic ice nucleation in the stem, ice spread into the leaves. On the leaf lamina, it was possible to differentiate between initial freezing in the veins and subsequent freezing in the mesophyll. The spread of ice followed the venation and could usually be tracked to third-order lateral veins. The exception was in mature leaves of Buxus sempervirens L., where large ice lenses formed in the central mesophyll lacunas. Longitudinal ice propagation within veins was faster (0.3–4.7 cm s⁻¹) than measured in earlier studies (0.25–2.7 cm s⁻¹). Peculiar leaf freezing patterns indicated that lateral ice propagation in the vascular bundles may take significantly longer than longitudinal ice propagation. Within the vascular bundle, the exact sites of initial vein freezing could not be resolved. However, the observed freezing patterns combined with chemical theory and anatomical structures suggest that initial freezing most probably occurs within the xylem vessels and tracheids. Ice barriers appeared to be present in leaf laminas of Cinnamomum camphora (L.) J. Presl., resulting in freezing of small mesophyll compartments produced by sclerenchymatic bundle sheath extensions. The IDTA was demonstrated to be a highly efficient method for resolving peculiarities of ice propagation at the plant tissue level.