RADIATION AND CONVECTION IN CONIFERS

The transfer of energy to and from a conifer branch involves solar radiation, thermal radiation from the ground, atmosphere, and surroundings, thermal emission by the branch, and free convection in still air and forced convection in wind. It is necessary to know the actual surface area of the branch, the effective area for absorbing sunlight, the effective area for absorbing long wave thermal radiation and for emission, and the free and forced convection coefficients. These parameters are determined using silver castings of blue spruce and white fir branches suspended in an evacuated radiation chamber and in a wind tunnel. The actual surface area of a branch is determined by means of an electrolytic technique. Numerical examples are given for energy transfer in a natural environment for conifers and comparison is made to a broad deciduous type of leaf. The role of transpiration in the energy transfer process is discussed.