Short Rotation Forestry in Loblolly Pines

Alan P. Bruce, James River Corporation, Pennington, Alabama

The use of trade, firm, or corporation names in this paper is for the information and convenience of the reader. Such use does not constitute official endorsement or approval by the U.S. Department of Agriculture of any product or service to the exclusion of any other that may be available.

ABSTRACT

The potential for developing and expanding SRIC (short rotation intensive culture) forestry in the South (southern United States) is greater than ever before. Increased demand for wood across the South makes the high cost of SRIC forestry more favorable to wood products companies. Technological developments in herbicides, genetics and mechanical treatments are making SRIC forestry more biologically and economically feasible. James River Corporation is currently practicing SRIC forestry on both their pine and hardwood timberlands in the South. Loblolly pine and eastern cottonwood are James River's primary SRIC species. Sycamore and sweetgum are being managed on a project basis.

INTRODUCTION

Short rotation intensive culture (SRIC) forestry is being conducted in a limited manner across the South. Traditionally, SRIC forestry has focused on hardwood species such as eastern cottonwood, American Sycamore, sweetgum and exotic species. Several factors have limited SRIC forestry in the South including: 1) the high cost of silviculture; 2) inconsistent results due to complex species-site relationships; and 3) the relative abundance of natural hardwood fiber.

Pine plantation forestry is a significant practice across the South. Approximately 12 million ha (16 percent) of southern forests are pine plantation type (Kelly 1994). The intensity of silviculture and the length of rotations in southern pine plantations varies widely. Conventional plantation silviculture, as generally practiced over much of the past 30 years, will not be characterized as SRIC in this paper. The potential for SRIC pine has increased dramatically in the past few years with the development of cost effective herbicides and plows. These technologies could make 12 to 16 year, high yield pine rotations feasible.

SRIC PINE ON JAMES RIVER TIMBERLANDS

Background

James River currently owns about 40,000 ha of predominately pine timberlands. This timberland base is the primary softwood supply source for James River's Naheola pulp and paper mill, located in west-central Alabama. Almost all of this timberland is located within 60 km of the mill.

James River is managing multiple rotation lengths at varying intensities which are site specific. For the past five years, SRIC pine plantations have been established on James River's higher quality sites. These sites are suitable for SRIC due to gentle terrain and high growth potential.

SRIC treatments

A typical SRIC establishment site is a recently clear-cut, 25-year-old, pine plantation. The SRIC prescription begins with harvesting as all stumps are cut as low as possible. Following the harvest, a broadcast burn is conducted to reduce logging slash and enhance plowing operations.

A Savannah Forestry combination plow is then pulled across the site on three m intervals. The plow is pulled with a 150 kW crawler tractor equipped with a V-shear blade. The V-shear blade is used to push large debris to either side and clip residual sub-merchantable trees. It is not used for shearing stumps off at ground level. The blade is generally run in a slightly raised position and does clip the tops of taller stumps.

The Savannah Forestry combination plow cultivates, fractures, subsoils and beds. This plow has a coulter, blade plow, subsoiler tine, and stump-jump bedding discs. The coulter cuts debris and splits stumps associated with an uncleared site. The blade plow which follows behind the coulter cultivates 15 cm deep, undercutting hardwood root stocks and stumps.

The subsoiler follows the blade plow and fractures the soil 60 to 70 cm deep. Four independent stump jumping bedding discs follow the subsoiler. These discs cultivate a bed 2.4 m wide. These discs are hydraulically actuated at 42 to 56 kg cm^-2 psi. As a disc hits a stump the hydraulic cylinder on the jump arm allows the disc to give way and roll over the top of the stump. The remaining three discs remain in the ground cultivating.

Figure 1. Illustration of a Savannah Forestry Equipment, Inc., Combination Plow used by James River Corporation in Alabama

Figure 2. Illustration of a soil profile after plowing with the Savannah Combination Plow

Plowing is normally done between June and November. The following January through March, bareroot, second generation, loblolly pine seedlings are planted. Shortly after planting in April, a grass control herbicide is broadcast, or directed in 1.5 m bands, over the pine seedlings. Some soils are fertilized with a 50 cm banded application as early in the spring as trafficability allows.

Results

Long-term results from James River's SRIC silviculture are unknown. The oldest trees under the SRIC regimen completed their fifth growing season in 1993. The short-term results appear dramatic with a significant growth response.

Herbaceous weed control appears to be the most growth enhancing SRIC treatment applied across James River's sites. From hilly, sandy loam sites to flatwoods, silty clay sites, herbaceous weed control consistently appears to significantly increase seedling growth. Table 1 shows the early growth response of seedlings to herbaceous weed control on James River research plots.

Three-in-one combination plowing appears to enhance growth on most James River sites, however, at varying degrees. Tree growth response to combination plowing appears to be soil texture related on James River sites. Compacted sandy loams to sandy loam clays seem to benefit the most from plowing. Table 2 shows the growth response to three-in-one combination plowing on a loam topsoil-clay subsoil site. This site was treated with hexazinone herbicide which provided herbaceous weed control to both the treated and untreated areas. Note that after three growing seasons the plowed area trees contain more than twice the volume of unplowed area trees.

¹Diameter is measured at ground line.

Table 3 shows the results of combination plowing versus no plowing and conventional bedding. Plastic, silty clays respond significantly to combination plowing, but not significantly more than from conventional bedding. James River research indicates that the difference between the deep fracture of subsoiling versus conventional bedding on silty clays is not significant on seedling growth.

^aAll three treatments included shear and rake site preparation and herbaceous weed control applied shortly after planting in 1991. This search is located on Wilcox silty clay.

CONCLUSIONS

Reports from scientists (Busby 1992) familiar with early herbaceous weed control experiments indicate a potential of a three-year reduction in rotation length when this SRIC treatment is conducted. With the additional treatment of deep soil fracture through combination plowing, rotation length could be shorter. As such, James River believes 12 to 14 year, high yield, SRIC pine rotations are quite feasible.

LITERATURE CITED

1. Busby, Ronald L. 1992. An economic evaluation of the use of Oust for herbaceous weed control in loblolly pine plantations. Southern Journal of Applied Forestry 16(1): 40-47.
2. Kelly, John 1994. Telephone conversation regarding acreage of pine plantation type forests in southern United States. John Kelley, Forest Inventory and Analysis Group, USFS, Starkville, MS.

File posted on March 5, 1996; Date Modified: February 21, 1999