Regenerating uneven-aged stands of loblolly and shortleaf pines: the current state of knowledge

Periodic regeneration is crucial to creating or sustaining uneven-aged (UEA) stands of loblolly (Pinus taeda L.) and shortleaf (P. echinata Mill.) pines. Although both species are shade intolerant, they have silvical characteristics that are conducive to natural regeneration in UEA stands. Their seed production is fairly consistent and good, and the wind-disseminated seeds are well dispersed throughout the stand. The disturbed seedbed resulting from periodic logging is favorable to germination, and established seedlings can recover from a fair degree of logging damage. Seedlings are moderately shade tolerant when young, and they respond well when released from either competing understory vegetation or overtopping trees. The key to successful regeneration in UEA pine stands involves regulating the stocking and structure of the merchantable portion of the stand with careful logging and periodically controlling nonpine vegetation, typically with selective broadcast herbicides(1). Current after-cut guidelines call for basal areas of 10 to 14 m(2)/ha, maximum diameters of 35 to 55 cm, and a q factor in the vicinity of 1.2 for 2.5 cm DBH classes. Applying these guidelines results in a stand with an irregular canopy containing multidimensional gaps. Stand basal area is not allowed to exceed 17 m(2)/ha during the cutting cycle because regeneration would be adversely affected by shading and root competition. Pines over 40 cm in DBH have been found to be favorable to regeneration because of increased seed production and reduced logging traffic needed to remove harvested trees. Regeneration is most difficult to secure on good sites because of intensive nonpine competition, but selective herbicides are available that will release pine regeneration from competing nonpine vegetation. Due to the increased interest in UEA silviculture, we present an overview in this paper of more than 50 years of research and experience in regenerating these two important species in UEA stands principally using single-tree selection. (C) 2000 Elsevier Science B.V. All rights reserved.