Long-Term Development of Regeneration Under Longleaf Pine Seedtree and Shelterwood Stands

Well-stocked mature longleaf pine (Pinus palust r is Mill . ) s tands were cut tofive res idual basal areas in 1957, namely 9,18,2 7.36, and 45 ft’ per ac, to observe the effect of s tand densi ty on seed product ion and seedl ing establ ishment . Seedl ings, mainly from the 195.5 or 1961 seed crops, were establ ished in treated stands. Al l pines on net 0.9 ac plots were remeasured in I991 to determine rhe effect of res idual pine den@ on development of the regenerat ion. Even the l ightest residual overstory converted the structure of 29to ?Syr-old ingrowth in to rhe reverse-Jdiameter class dis tr ibut ion characteris t ic of uneven-aged stands. Four or s ix residual trees , now compris ing 7 co IO ft’ basal area (ba)lac, reduced ingrowth basal area to about half that of same-aged stands releasedfrom overstory competi t ion. Merchantable volume of ingrowth under these low residual densi t ies averaged 40% of that in released stands. Mean annual per ac volume increment of ingrowth averaged 21 to 22 fi” under the 9 fedens@ but did not exceed 7fti under any residual densi ty above this . The potent ia l impact of signi f icant growth reduct ions should be taken into account when considering uneven-aged management methods for longleaf pine. South. J. Appi. For. 17( I ):IO-IS. L ongleaf pine (Pinuspalustris Mill .) is generally considered the most intolerant of the southern pines (Baker 1949). It is notoriously intolerant of competition from any source, espycially overtopping trees including parent pines. Longleaf pine regeneration in old-growth forests was largely confined to openings where it was free to develop (Wahlenberg 1946), and some seedlings could reach a fire-resistant size in a relatively short time. The early growth of seedlings under a pine canopy, if they survive, is very slow (Boyer 1975, Maple 1977), even under a light overstory. Growth rapidly declines as overstory density increases. About 70% of the growth reduction observed under an overstory of 90 ft* ba/ac was reached under 30 ft* (Boyer 1963). Thecompeti t ive influenceof individual seed trees or forest wal ls on longleaf pine seedlings decreases with distance, but may extend 50 ft or more from the base of parent trees into an opening, well beyond the influenceof thecrown (Smith 1955, Walker and Davis 1956, Boyer 1963). This suggests competi t ion for moisture and nutr ients . The competi t ion zone seems to extend farther from the parent tree on poor than on good si tes . As an early successional species, maintained through periodic fire, longleaf pine has appeared best adapted to management in even-aged stands. Alternatives to traditional evenaged management are now being promoted for this species. They include uneven-aged management, such as group selection, and also variations on even-aged management that 10 SJAF 17(l) I993 include retention of a few or many residual trees through all or most of a second rotation, resulting in a stand comprised of two distinct age classes. Such alternatives to conventional even-aged management wil l maintain a relat ively continuous cover of mature trees and are expected to improve and extend habitat for the red-cockaded woodpecker and other fauna and flora associated with these condit ions. The potential impact of residual t rees on the development, structure, and yield of the replacement stand is not known due to the lack of information on the long-term growth response of longleaf pine regeneration retained under a parent dverstory. Such information is needed in order to adequately evaluate the consequences of management systems that lead to stands consist ing of two or more age classes. An opportunity to gain some timely information on the question of s tand development under residual longleaf pines was available on the Escambia Experimental Forest’ in southwest Alabama. There, a study was begun in 1957 to determine the effect of longleaf pine s tand densi ty on seed production and seedling establishment. Longleaf pine regeneration was established shortly before or soon after parent stands were thinned to prescribed densi t ies . Two addit ional s tudies, superimposed on parts of the original s tudy, provided some information on development of the regeneration. I Maintained by the Southern Forest Experiment Station, USDA Forest Service. i n c o o p e r a t i o n w i t h t h e T . R . M i l l e r M i l l C o m p a n y .