Water use of short-rotation coppice American sycamore (Platanus occidentalis L.) for bioenergy during establishment on marginal land in the North Carolina Piedmont

Abstract

American sycamore (Platanus occidentalis L.) is a hardwood species that can be integrated into short-rotation coppice (SRC) production systems for bioenergy in the southeastern USA. Due to high growth rates and low input requirements, sycamore is regarded as a promising second-generation bioenergy woody crop suitable for degraded or marginal lands. However, little is known about sycamore water use for the conditions of North Carolina (NC), especially during the establishment year when trees are most sensitive to soil water deficits. We evaluated energy fluxes and actual crop evapotranspiration (ETc act) rates of sycamore SRC during the establishment year on marginal land in the Piedmont physiographic region of NC. Our overall goal was to better understand the factors controlling the evaporative demand of sycamore and its sensitivity to drought stress during establishment. Total ETc act was 482 mm, which was 95% of the total rainfall at the site. ETc act rates increased with precipitation and with tree development, reaching a maximum of 5.7 mm d−1. Although severe water stress was not observed during the study period, a moderate drought occurred from mid-August to mid-September, during which a 13-day drying cycle caused ETc act rates to decrease by 30%. The sycamore SRC transitioned from an “energy-limited” to a “water-limited” ETc act regime when water content in the upper 5 cm of soil was about 0.10 m3 m−3, indicating that the sycamore field relied on water available within the upper soil layers. Measurements suggested that trees may not yet have developed a root system sufficient to sustain transpiration during dry spells and that water use of the sycamore field was highly coupled to precipitation during the establishment year.