Effects of environmental factors and management practices on microclimate, winter physiology, and frost resistance in trees

Abstract

Freezing stress is one of the most important limiting factors determining the ecological distribution and production of tree species. Assessment of frost risk is, therefore, critical for forestry, fruit production, and horticulture. Frost risk is substantial when hazard (i.e., exposure to damaging freezing temperatures) intersects with vulnerability (i.e., frost sensitivity). Based on a large number of studies on frost resistance and frost occurrence, we highlight the complex interactive roles of environmental conditions, carbohydrates, and water status in frost risk development. To supersede the classical empirical relations used to model frost hardiness, we propose an integrated ecophysiologically-based framework of frost risk assessment. This framework details the individual or interactive roles of these factors, and how they are distributed in time and space at the individual-tree level (within-crown and across organs). Based on this general framework, we are able to highlight factors by which different environmental conditions (e.g., temperature, light, flood, and drought), and management practices (pruning, thinning, girdling, sheltering, water aspersion, irrigation, and fertilization) influence frost sensitivity and frost exposure of trees.

Keywords: anthropogenic impact; carbon balance; environmental factors; frost resistance; microclimate; risk assessment; stress interaction; water status.

FIGURE 1

Strategies developed by trees to avoid or tolerate freezing stress and ice formation (adapted from Levitt, 1980).

FIGURE 2

Conceptual framework of processes involved in frost resistance development in trees. The microclimate (Frame A) results from interactions between the climate and spatial structure of tree canopies. Trees experiencing freezing events integrate ecophysiological and internal processes throughout the entire year (Frame B). Among these biophysical factors, the balance of total non-structural carbohydrates (e.g., sugars and starch reserves; Frame C) results from various source-sink interactions during the year. Water content (Frame D), is regulated by input-output fluxes, which may lead to embolism. Non-structural carbohydrates, water content, and previous year damage affect frost resistance (Frame E) and survival (Frame F). These interactions are modulated by either natural events (numbered 1–7) or anthropogenic events (numbered 8–13).