Effect of Canopy Competition on Tree Growth and Development in Pine Hardwood Mixtures

Abstract

Mixed species forests may benefit from the reduction in intraspecific competition, although the benefit of species mixing has been shown to vary depending on mixture composition and environmental conditions. This study sought to test the effect of species composition in mixed forest stands on canopy development and growth of loblolly pine (Pinus taeda), cherrybark oak (Quercus pagoda), and sweetgum (Liquidambar styraciflua). Even-aged, grid planted monoculture and mixed species forest plots were established with hardwood monoculture plots at a 741 Trees Per Hectare (TPH), and pine monoculture and mixed species plots established at 1482 TPH. Diameter at Breast Height (DBH), total height, height to live crown, ratio of live crown, leaf area index, and competition index were measured to assess tree growth and development. Sweetgum height increased in mixture with loblolly pine independent of competition, while loblolly pine diameter growth was reduced by competition with sweetgum. Cherrybark oak experienced a reduction in live crown ratio as a response to competition in mixture with loblolly pine, although neither species differed to their respective monocultures in radial or height growth. The difference between sweetgum-pine mixture and oak-pine mixture highlights the importance of mixture composition on individual tree growth and development.