Using silvicultural practices to regulate competition, resource availability, and growing conditions for Pinus palustris seedlings underplanted in Pinus taeda forests

In the southeastern United States, many forest managers are interested in restoring longleaf pine (Pinus palustris Mill.) to upland sites that currently support loblolly pine (Pinus taeda L.). We quantified the effects of four canopy treatments (uncut Control; MedBA, harvest to 9 [m.sup.2] x [ha.sup.-1]; LowBA, harvest to 5 [m.sup.2] x [ha.sup.-1]; and Clearcut) and three cultural treatments (NT, no treatment; H, herbicide release of longleaf pine seedlings; and H+F, herbicide release plus fertilization) on resource availability and growing conditions in relation to longleaf pine seedling response for 3 years. Harvesting treatments reduced competition from canopy trees but resulted in greater abundance of understory vegetation. Harvesting shifted the interception of light from the canopy to the subcanopy vegetation layer; however, total light availability at the forest floor increased with the intensity of canopy removal. Soil moisture was not affected by harvesting or by the cultural treatments. Foliar nutrient concentrations (N, P, and K) of longleaf pine seedlings generally increased with the intensity of the harvest treatment. Of the plant resources measured, we found that light was most strongly correlated with longleaf pine seedling growth and that incorporating the interception of light by subcanopy vegetation improved the relationship over that of canopy light transmittance alone. Key words: foliar nutrients, gap light index, longleaf pine restoration, resource availability, underplanting. Dans le sud-est des Etats-Unis, plusieurs amenagistes forestiers sont interesses a restaurer le pin des marais (Pinus palustris Mill.) sur des stations bien drainees presentement occupees par le pin a encens (Pinus taeda L.). Nous avons quantifie les effets de quatre traitements d'eclaircie du couvert dominant (temoin non traite; surface terriere residuelle de 9 [m.sup.2] x [ha.sup.- 1], MedBA; surface terriere residuelle de 5 [m.sup.2] x [ha.sup.-1], LowBA; et coupe a blanc) et de trois traitements culturaux (temoin non traite, TEM; application d'un herbicide autour des semis de pin des marais, H; et application d'un herbicide et d'une fertilisation, H+F) sur la disponibilite des ressources et sur les conditions de croissance en relation avec la reaction des semis de pin des marais pendant trois ans. Les traitements de coupe ont reduit la competition des arbres du couvert dominant, mais ont entrame une plus grande abondance de la vegetation sous couvert. La coupe a fait passer l'interception de la lumiere du couvert dominant a la strate de vegetation sous le couvert, mais la disponibilite totale de la lumiere au sol a augmente avec l'intensite de l'eclaircie du couvert dominant. L'humidite du sol n'a pas ete influencee par la coupe ou par les traitements culturaux. La concentration foliaire en nutriments (N, P et K) des semis de pin des marais a generalement augmente avec l'intensite des traitements de coupe. Parmi les ressources necessaires a la croissance des plantes que nous avons mesurees, la lumiere etait la plus etroitement correlee a la croissance des semis de pin des marais et cette relation etait amelioree en tenant compte de l'interception de la lumiere par la strate de vegetation sous le couvert dominant en plus de la transmission de la lumiere par le couvert dominant. [Traduit par la Redaction] Mots-cles: nutriments foliaires, coefficient de trouees lumineuses, restauration du pin des marais, disponibilite des ressources, plantation sous couvert.
Introduction In forested ecosystems, the combination of abiotic conditions and biotic interactions at the growing site largely controls the establishment success (i.e., growth and survival rates) of individual tree seedlings [...]