Effect of Six Site-preparation Treatments on Piedmont

The impact of weed control and fertili7Mion on incnajed tree growth is positive and significant but the effects on wood pmper6es are not well known. lncrernent axes mn, coUac@d from lobldly pine (pinus faeda L) trees growing on an existing site-preparation experiment in the lower Piedmont of Georgia at age 15. The levels of site praparation were: ldearcut only; P-chainsaw, 3-shear and chop; 4-shear. chop. and herbidde; 5-shear, rootrake. bum, and disk; 6-shear, rootrake. bum, disk, fertilize, and herbidde. TWO. 0.472 in. inclement CW?S wera aMacted at dk.h. from 36 trees representative of each slte-praparation treatment Wood basal-am-a growth increased signiticantly with increased sitepreparation treatment. The site-preparation treatments did not affect length of juvenility whiti averaged 10 years for all treatments. Average increment core specific gravity was not sfgni6cantly reduced with increased site preparation compared to the cuntrol treas. The diameter of the juvenile wood core. however. increased with increased site-preparation treabnant lNTROOUCTlON The pressure to produce wood fiber is leading to intensively managed plantations, which generally accelerate the early growth of the trees and reduce rotation length to maximize return on investments. The wood industry is now using intensive cultural treatments such as intensive site preparation, competition control, and fertilization to increase fiber production of southern pine. The impact of these intensive silvicultural treatments on increased growth is positive and significant, but their effect on wood properties is not well known. A site-preparation study established in 1982 to evaluate and understand the benefits of various site-preparation treatments on pine survival and growth provided the opportunity to examine the effects of various site-preparation treatments on wood properties. Increment cores, 0.472 in. in diameter, were collected from 1 S-year loblolly pine (Pinus faeta L.) established using six levels of site preparation. The increment cores were analyzed to determine the effect of site preparation treatment on annual earlywood and tatewood production, date of transition from juvenile to mature wood, and wood specific gravity. LITERATURE REVIEW In the Southeast a typical loblolly pine plantation can pmduce 50 to 110 @ of wood per acre per year. However, research (Borders and Bailey 1997) has shown that with intensive management practices, such as complete competition control, multiple fertilizations, and genetically improved stock, these growth rates can be increased to 250 to 350 ft! per acre per year. These growth rates compare well with the fastest growing loblolly pine anywhere in the world. A radial cross-section of a pine stem contains three zones of wood: l-core or crown-formed wood, which is produced by immature cambiim in the vigorous crown and has anatomical, chemical, and physical properties that differ from that of mature wood; 2-transition wood, a zone where wood properties are changing rapidly before wood reaches maturity; and 3-mature wood (Clark and Saucier 1989). Juvenile wood is characterized as having lower specific gravity, shorter tracheids, thinner tracheid walls, larger lumens, lower percent latewood, and lower alpha cellulose content than that of mature wood. In the longitudinal direction there is a core of crown-formed wood sunounding the pith from butt to tip of stem surrounded by a band of transition wood from butt to base of live active crown surrounded by a wide outer band of mature wood (Bendtsen and SentI 1986). Both crown-formed and transition wood is commonly referred to as juvenile wood. The definition of southern pine wood quality depends on the product for which the wood is used. High specific gravity is almost always considered a desirable wood quality trait. High specific gravity is positively correlated with wood strength and stiffness. Wood from young fast-growing pine plantations often has physical and mechanical properties that make it less desirable than older, slower grown wood for structural lumber because of large volumes of low specific gravity, juvenile wood (Bendtsen 1986, Bendtsen and Senff 1986, Bendtsen and others 1988, Biblis 1990, McAister and Clark 1991, Pearson and Gilmore 1971). Wood and fiber properties that affect paper making include specific gravity, cellulose percent and other chemical constituents, fiber length, and microfibril angle (Erickson and Arima 1974, Megrow 1985. Schmidtling and Amburgey 1977, Zobel and Blair 1976). Paper from juvenile wood will have good tensile, burst, fold and sheet smoothness but tower tear and opacity than paper made from mature wood pulp (Zobel and Blair 1976). Higher specific gravity mature wood pulp will result in higher pulp yield and is generally associated with longer fibers with increased tear for liner-board and kraft sack papers. The number of years a tree produces juvenile wood at a fixed height level (juvenile period) does not diier between slash and loblolly pine when the species are planted at the same location but does vary with geographic location (Clark and Saucier 1989). The length of the juvenile period of slash and loblolly pine in the Southeast decreases geographically from north to south. In loblolly and slash pine, the period of juvenile wood formation decreases from 10 to 14 years in the Piedmont to 6 to 8 years in the Gulf and Atlantic Coastal Plain. In a study by Cregg and others (1988) it was observed that the transition from earlywood to latewood occurred 1 month earlier in a year of low rainfall and high ’ Paper presented at the Tenth Biennial Southern Siivicultural Research C%NIference, Shreveport, LA. February 16-18. 1999. ’ Research Wood Sc&tist and Research Ecologist. USDA Forest SetiCe. Southern Research Station. Athens, GA 30602. respectively. spring evaporate demand than in a year of low evaporate demand and high rainfalt. Whether an early transition to btewood leads to an annual ring with a high percent of latewood, and thus high specific gravity, depends on the growing conditions that occur after the transition to l&wood production. Based on Moehdng and Ralston’s (1967) work it appears the moisture supply and pan evaporation in the months of July, August, September, and October control the amount of latewood that is produced. The use of herbiis to reduce competing vegetation in a pine plantation will increase soil moisture and nutrients available for pine growth. Thus, competition controls could significantly influence the proportion of earlywood and latewood tracheids produced. Fertilization at stand establishment with no competition control will stimulate competition growth and thus could reduce soil moisture available for latewood growth. The objective of this study was to determine the effect of increasing intensity of site preparation from no treatment, shear and chop with and without herbicide to shear, rootrake, bum, and disk with and without herbicide and fertilization on annual growth of earlywood, latewood, and wood specific gravity of loblolly pine in the lower Piedmont of Georgia. PROCEDURES The tobloliy pine plantation sampled was hand planted with improved toblolly pine seedlings in early 1982 at a spacing of 6by 1 Oft (Edwards 1994). The original stand of toblolly pine and mixed hardwoods on the study tract was harvested in 1981. The 84-acre study tract is located in the tower Piedmont of Georgia, at the Hitchiti Experimental Forest and has an average site index of 80 at base age 50 years. Six site-preparation treatments were evaluated in the study and are listed in order of increasing intensity: