ENERGY PARTITIONING INFLUENCED BY TREE SPACING

An energy partitioning experiment was set-up within an experimental ag roforest site at Cloich forest, near Edinburgh. Measurements of turbul ent heat fluxes were made - during non stress conditions - both direct ly by eddy-covariance techniques and in the case of latent heat flux i ndirectly through closure of the energy budget equation. These measure ments were made simultaneously in the thinned plots (one plot at a tim e) and a reference plot to eliminate differences due to external atmos pheric conditions. Observed values of Bowen ratio ranged from I to 3.5 , with significantly lower values in the thinned plots compared with t hose measured in the reference plot. On separation of the Bowen ratio into its two components, it was found that sensible heat flux remained constant between plots. The latent heat flux, however, increased as t he tree density was reduced. A simple model of the evaporation from th e forest plots based on the Penman-Monteith equation and incorporating an under-storey component was developed and was able to accurately re plicate the observed results.