Energy Balance Relative to Percent Plant Cover in a Native Community

Abstract

Net radiation (Rn) and evapotranspiration (ET) were poorly correlated during both a "wet" and a "dry" period on native range near Sidney, Montana within each of five levels of vegetational cover. The ratio ET:Rn fluctuated greatly in all cases and was generally higher during the period of higher rainfall. During dry periods, substantial amounts of energy were dissipated as heat flux to the atmosphere. Maximum evaporation and/or transpiration from 0%, 25%, 50%, 75%, and 100% cover occurred for 12 days after rainfall and was, respectively, 0.7, 0.8, 1.1, 0.3, and 1.9 times the evaporation from a Class A evaporation pan. Total evapotranspiration for the season was 21% lower and dry matter production was 14% higher with 50% cover than with complete cover. Water use from 75% and 25% cover was similar to that from 50% cover, but forage yields were 5% and 14% less, respectively, than from complete cover.