PS 33-11 - Growth and biomass allocation during early loblolly pine development as influenced by fertilization and herbicide

Wednesday, August 14, 2019
Exhibit Hall, Kentucky International Convention Center
Gabriel W.D. Ferreira, Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, Benjamin Rau, New England Water Science Center, USGS, Northborough, MA and Doug P. Aubrey, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA
Background/Question/Methods: Silviculture practices influence tree development, although the growth response and biomass allocation in intensively managed forests might change throughout stand development. We designed an experiment to evaluate the influence of nitrogen (N) and herbicide application on the growth and above- and below-ground biomass allocation in young Pinus taeda plantations in southeastern US. Five treatments with eight replications each were tested: no herbicide and no fertilization input (control); only herbicide input; herbicide and half of operational N fertilization rate; operational herbicide and fertilization (commercial rates); and increased stand density (60 % higher) with operational herbicide and fertilization rates. Allometric equations generated from destructive harvests were applied to annual diameter measurements to estimate plot-level biomass and allocation across the first five years of stand development.

Results/Conclusions: Control trees exhibited 1.8- and 2.7-fold smaller diameter and height, respectively, than trees from the other treatments, and yielded the lowest biomass. Differences in biomass allocation were prominent after the third growing season. Overall, the increased density treatment yielded the greatest biomass; the half-N and the operational treatments did not differ but yielded higher biomass than herbicide application only. All treatments but the control showed above:below ground ratios > 2. During the two first years, needles accounted for 30 – 40 % of total biomass, but decreased to less than 20 %. The proportion of coarse-roots remained stable (~ 40 %). Stem and branch biomass increased with stand development and were responsible for ~ 35 and 15 % of total biomass, respectively. Proportionally, control trees tended to allocate more biomass to roots and needles than trees from other treatments. Our results indicate that controlling competing vegetation is critical during early stand development and that N amendments may not be necessary in the earliest growing stages as organic mineralizable-N may satisfy tree demand. Increased stand density might be an alternative to increase production while not sacrificing individual quality. Adjustments in the current N management may maintain productivity while reducing ecological risks.