Stem Sinuosity, Tree Size, and Pest Injury of Machine-Planted Loblolly Pine with Bent versus Straight Taproots

Abstract

Twenty-four machine-planted stands of loblolly pine (Pinus taeda L.) of ages 3 to 10 yr were sampled near Athens, GA, to compare stem sinuosity, tree size, and pest injury of trees with bent versus straight taproots. Based on a 0- to 8-point index, the average level of stem sinuosity was medium (x̄ = 2.6; n = 1,327 trees). Trees of high or low stem sinuosity index were identified near each of ten points per site, and one was selected to best represent each level (n = 240 pairs). Seventy-two pairs were excavated, and of these, 62 and 82 trees had bent and straight taproots, respectively. Levels of stem sinuosity were medium or high for 77% of trees with bent taproots, while they were low for 71% of trees with straight taproots (chi-square P = 0.001). Trees with bent taproots were 7% to 9% smaller in stem diameter and height, while their stem sinuosity index was over twice that of trees with straight taproots (P ≤ 0.01). Taproot azimuth did not differ significantly (P > 0.20) from planting row azimuth, indicating that bent taproots from machine planting remained confined to the planting slit. Although biological mechanisms were not identified, results indicate a potentially problematic association between bent taproots and reduced stem quality of loblolly pine.