Sycamore and sweetgum plantation productivity on former agricultural land in South Carolina
Former agricultural lands in the southern US comprise a significant land base to support short rotation woody crop (SRWC) plantations. This study presents the seven-year response of productivity and biomass allocation in operational-scale, first rotation sycamore (Plantanus occidentalis L.) and sweetgum (Liquidambar styraciflua L.) plantations that were established on drained Ultisols which were historically planted in cotton and soybeans. Three plantation systems, sycamore open drainage, sycamore plus water management, and sweetgum open drainage were established on replicate 3.5–5.5 ha catchments. Height, diameter, and mortality were measured annually. Allometric equations, based on three, five, and seven year-old trees, were used to estimate aboveground biomass. Below-ground biomass was measured in year-five. Water management did not affect sycamore productivity, probably a result of a 5 year drought. The sycamore plantations were more productive after seven growing seasons than the sweetgum. Sycamore were twice the height (11.6 vs. 5.5 m); fifty percent larger in diameter (10.9 vs. 7.0 cm); and accrued more than twice the biomass (38–42 vs. 17 Mgha-1)of the sweetgum. Sweetgum plantation productivity was constrained by localized areas of high mortality (up to 88%) and vegetative competition. Mean annual height increment has not culminated for either species. Diameter growth slowed in the sycamore during growing seasons five through seven, but was still increasing in the sweetgum. Both species had similar partitioning of above-ground (60% of total) and below-ground biomass (40% of total).