Understory Transpiration Rates Following Stand Density Reduction in a Coast Redwood Forest

Abstract

In forests where the overstory canopy has been disturbed, evapotranspiration (ET) by the understory may be the main flux of water back to the atmosphere. The ability to take field measurements of water use by understory plants, therefore, is vital for a complete ecosystem water budget. However, little research has been apportioned to directly measuring understory water use, and the technology to do so is thus limited. Portable ET chambers have been used to measure ET rates in agricultural fields, grasslands, and deserts, but not in a forest understory. Thus, a portable rapid chamber which can be easily deployed and collect quick ET measurements of single plants was developed for measuring understory plant water use in logged watersheds in coastal California. Mean understory ET rate was highest in the watershed with the lowest residual basal area ( = 87  56 mm/day) and lowest in the control watershed ( = 31  19 mm/day). Multiple regression modeling indicates that the difference in ET rate between watersheds is caused by freed soil water as a result of overstory tree removal. These results imply that understory water use is likely significant in harvested watersheds, and should be quantified at the landscape scale.