Estimating forest canopy effects on summer thermal cover for Cervidae (deer family)

Abstract

Operative temperatures of five members of the deer family under different forest canopies during summer were estimated. Sky view factors and effective leaf area indices were obtained from hemispherical photography. These were combined with radiation regime, ambient air temperature, wind speed, and other relevant factors to obtain operative temperature. Upper critical temperatures were significantly related to operative temperature in the open (r² = 0.65; p < 0.05). To assess the thermal cover value of different canopy closures, simultaneous operative-temperature values as a function of canopy closure were estimated by simulation. Operative temperature decreased sharply with increasing crown closure up to about 30% crown closure, and then more gradually. Crown-closure values providing thermal cover under different ambient temperatures are summarized for the five deer taxa. Crown-closure classes as commonly depicted on forest cover maps correctly rank the effectiveness in providing summer thermal cover (r² = 0.91; p < 0.05).