The Energy Budget within and above an Oak Forest in a Temperate-Humid Climate

Measurements of the energy budget components were made below and above an oak forest about 10 m tall with LAI about 2.5 over the summer (June-October) of 2007 in the Okmulgee area in eastern OK. These measurements were part of an extensive classic experiment in OK to evaluate the importance of energy and turbulent transfer processes in large vegetation systems on the regional weather dynamics that occur in that part of United States. Flux towers were used to measure the radiation, sensible, and latent heat fluxes. Estimated normalized difference vegetation index (NDVI) averaged about 0.6 and did not show much change for the forest canopy density during the period of the study. Bowen ratio values ranged from 0.1 to 0.5 with net radiation ranging from 300 to 700 W m-2 above the canopy and from 50 to 100 W m-2 below the canopy. The 30-minute measurements of the energy budget closure were slightly better than 75%. Total daily evaporation averaged about 4 mm and 1 mm above and below the canopy, respectively, as the soil volumetric water content ranged from 0.2 to 0.45 m3 m-3. The near potential evaporation values were the result of the pervasive wet summer conditions caused by the many days of persistent rain events that occurred during the period of the study. The wind speed, sensible and latent fluxes inside the canopy were about 30%, 16% and 20%, respectively, of their above-canopy values, with only slight variations in the vertical for the humidity and air temperature. The analysis of the weather variables and the energy budget in this study suggests the low LAI of the forest can sustain a strong coupling between the dynamic turbulent transfer processes above and below the forest canopy.