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.) pin es. Although both species are shade intolerant, they have silvical characte ristics that are conducive to natural regeneration in UEA stands. Their see d production is fairly consistent and good, and the wind-disseminated seeds are well dispersed throughout the stand. The disturbed seedbed resulting f rom 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 successfu l regeneration in UEA pine stands involves regulating the stocking and stru cture of the merchantable portion of the stand with careful logging and per iodically controlling nonpine vegetation, typically with selective broadcas t 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 vicini ty of 1.2 for 2.5 cm DBH classes. Applying these guidelines results in a st and with an irregular canopy containing multidimensional gaps. Stand basal area is not allowed to exceed 17 m(2)/ha during the cutting cycle because r egeneration would be adversely affected by shading and root competition. Pi nes over 40 cm in DBH have been found to be favorable to regeneration becau se of increased seed production and reduced logging traffic needed to remov e harvested trees. Regeneration is most difficult to secure on good sites b ecause of intensive nonpine competition, but selective herbicides are avail able 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 regenerat ing these two important species in UEA stands principally using single-tree selection. (C) 2000 Elsevier Science B.V. All rights reserved.