Clearcutting upland forest alters transpiration of residual trees in the riparian buffer zone

Our objectives are (1) to compare tree sap flux density (Js in g cm−2 d−1) and stomatal conductance (Gs in mmol m−2 s−1) across five dominant species, red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera), loblolly pine (Pinus taeda), and oak species (Quercus spp.), (2) to quantity riparian buffer stand transpiration (Es in mm d−1), and (3) to link riparian buffer Es of residual trees to stream discharge. In June 2010, the above species were instrumented with sap flow sensors in a pair (HF1 and HF2) of 12 hectare gauged watersheds. HF1 was clearcut, leaving a 15.2-m riparian buffer around the stream, and HF2 was the reference. Trees were harvested in the riparian buffer reducing HF1 riparian buffer basal area by 27%. The riparian buffer growing season net radiation increased from 11.9 W m−2 preharvest to an average of 24.3 W m−2 postharvest. HF1 stream growing season discharge increased dramatically (150%) from the preharvest to postharvest period. HF1 2010 preharvest growing season soil moisture was 22.5%. HF1 postharvest growing season soil moisture was 28.5% in 2011, 26.5% in 2012, and 27.2% in 2013. HF2 canopy cover, energy input, and soil moisture showed little change over the same period. From preharvest to postharvest, mean daily growing season Js of trees in HF1 increased in all species. A reduction in HF1 Gs was less evident over the study vapour pressure deficit range in loblolly pine, red maple, and tulip poplar than in oak and sweetgum during the postharvest period. HF1 residual trees in the riparian buffer used 43% more water in growing season postharvest (314 mm) than growing preharvest (220 mm) period. This resulted in an 8% reduction in stream discharge because of an increase in riparian buffer Es. Although clearcutting increased stream discharge, we conclude that the increase in transpiration by the residual trees in the riparian buffer will, at least, partially mitigate the hydrologic effects of forest removal through increased transpiration. Copyright © 2015 John Wiley & Sons, Ltd.