Effects of land-use change and drought on decadal evapotranspiration and water balance of natural and managed forested wetlands along the southeastern US lower coastal plain
Forested wetlands are important in regulating regional hydrology and climate. However, long-term studies on the hydrologic impacts of converting natural forested wetlands to pine plantations are rare for the southern US. From 2005-2018, we quantified water cycling in two post-harvest and newly-planted loblolly pine (Pinus taeda) plantations (YP2-7, 2-7 yrs old; YP2-8, 2-8 yrs old), a rotation-age loblolly pine plantation (MP, 15-28 yrs old), and a natural bottomland hardwood forest (BHF, > 100 yrs old) along the lower coastal plain of North Carolina. We quantified the differences in inter-annual and seasonal water balance and trends of evapotranspiration (ET) using eddy covariance over 37 site-years and assessed key climatic and biological drivers of ET. We found that the rotation-age plantation (MP) had higher annual ET (933 +- 63 mm) than the younger plantations (776 +- 74 mm for YP2-7 and 638 +- 190 mm for YP2-8), and the BHF (743 +- 172 mm), owing to differences in stand age, canopy cover, and micrometeorology. Chronosequence analysis of the pine sites showed that ET increased with stand age up to 10 years, then gradually stabilized for the remainder of the rotation of 28 - 30 years. YP2-8 was sensitive to water availability, decreasing ET by 30 - 43 % during the extreme 2007 - 2008 drought, but reductions in ET at MP were only 8 - 11 %. Comparing to BHF, ditching with management enhanced drainage at YP2-7 and YP2-8, while drainage was lower at the mature pine site. This study provides insight into land use-hydrology-climate interactions that have important implications for forested wetland management in a time of rapidly changing environmental conditions of the LCP of the southern US.