Forage frost protection potential of conifer silvopastures

In temperate climates, forages are frequently held in a near dormant state at both ends of the growing season due to episodic radiation frost. During these periods, air temperature is frequently adequate for forage growth to supply feed for grazing animals. The effect of thermal radiation from conifer tree canopies on forage canopy temperature was evaluated for a silvopasture with variable tree density. A long-wave radiation-sensitive sensor for measuring temperature at the forage canopy level was designed, tested, and used to approximate night time forage canopy temperature during the autumn of 1999 and 2000 and spring of 2000. Temperature from the designed sensor correlated linearly with forage canopy temperature measured with an infrared thermometer with a slope of 1.0, a 0.9 °C offset, and an r2 of 0.999. The response of sensor temperature to night sky shading by trees was also linear. Under 77% tree cover sensor temperature remained within half a degree of air temperature, however, under 7% cover averaged 10.4 °C below air temperature during radiation frost events. The results of this study indicate that a well designed silvopasture can potentially extend the grazing season period on both ends in regions were radiation frosts are prevalent.