The effects of spacing and thinning on stand and tree characteristics of 38-year-old Loblolly Pine

The effects of early and continuous density control on the characteristics of mature loblolly pine (Pinus taeda L.) were measured at age 38 and analyz ed. Trees in plots planted at spacings of 1.8x1.8, 2.4x2.4, 2.7x2.7, 3.0x3. 0, and 3.7x3.7 m were either left unthinned or thinned every 5 years beginn ing at age 18, to residual basal areas of 27.5, 23.0, 18.4, and 13.8 m(2) h a(-1). Toes thinned from plot buffer zones at age 38 were selected to repre sent a final harvest cross-section of each treatment for evaluation of hole form, component biomass, and crown architecture. Volume and biomass of cut trees from all thinnings were included with the age 38 data fur stand leve l yield comparisons. Results show thinning effects were generally more pron ounced than spacing effects. Trees of the same diameter at breast height an d total height from heavily thinned stands had more cylindrical lower boles , more upper stem taper, longer crowns with more and larger branches, more total foliage, and hence more biomass than trees from unthinned or lightly thinned stands. All levels of thinning increased the yield of the stand in terms of foliage and branch biomass, while only light or moderate thinning increased bole biomass and volume yields. The magnitude of these difference s are presented. (C) 2000 Elsevier Science B.V. All rights reserved.