Productivity, crown architecture, and gas exchange of North Carolina and Oklahoma/Arkansas loblolly pine families growing on a droughty site in southeastern Oklahoma

Biomass production, crown architecture, leaf gas exchange, and specific gravity of North Carolina Coastal (NCC) and local Oklahoma/Arkansas (O/A) families of 15-year-old loblolly pine (Pinus taeda L.) were examined on an excessively droughty site in southeastern Oklahoma. The O/A family produced more branch and foliage biomass per hectare than the NCC family, but the two families produced equivalent amounts of stem biomass per hectare. The O/A family achieved its greater branch and foliage biomass production by virtue of supporting a higher number of live branches per tree. Photosynthetic capacity, needle stomatal conductance of water vapor, transpiration rates, and intrinsic water use efficiency, which were each measured periodically throughout the study, were similar for the two families, as were stand densities and survival. Specific gravity and DBH were similar for the two families, but trees of the NCC family were significantly taller than those of the O/A source. Given the comparable gas exchange characteristics and stem biomass production of the two families on this droughty site as well as the NCC familyʹs production of wood with fewer knots, we conclude that planting of the NCC family in favor of the local family on excessively drained soils in the northwestern portion of the loblolly pine range may be a justifiable management option.