Abstract
Computer simulation was used to study factors affecting freeze protection of trees using tree wraps and microsprinkler irrigation. Simulation results suggest tree wraps provide 1-2°C more freeze protection when air temperature decreases linearly rather than exponentially with time towards a minimum value. Tree wraps provided greater freeze protection when air temperature decreased rapidly (0.75°/h) than slowly (0.5 or 0.25°/h). Thus, variation in rate and pattern of the air temperature decrease among freeze nights may be responsible for inconsistent levels of freeze protection observed with tree wraps. Changing irrigation water temperature from 12 to 7 or 17° produced changes in trunk temperature under radiative, but not advective, freeze conditions. Simulation positioning of the microsprinklers to maximize coverage of the wrap surface with water provided better freeze protection than positioning that resulted in increased water interception. Increasing the wind speed from 0 to 10 m s-1 reduced the temperature of an irrigated wrapped trunk by 5°. Without irrigation, the temperature of a wrapped trunk was largely unaffected by wind speed. Reducing the humidity from 80 to 20% had a negligible effect on trunk temperature of irrigated wrapped trees under radiative and advective freeze conditions.