Disturbance from the Initial Harvest Implementing Uneven-aged Silviculture in a Pine-hardwood Stand in Southwestern Mississippi’

Logging disturbance is important in uneven-aged stands because harvests are frequent, merchantable trees are retained, and regeneration may be present. Logging disturbance was monitored during the establishment of a study testing the application of uneven-aged silvicufture in an irregularly aged, pine-hardwood stand. Disturbances were: (1) seedbed conditions averaging 56, 16, 9, and 17 percent of the area in undisturbed litter. disturbed litter, mineral soil, and logging slash, respectively, (2) a 44 percent reduction in the number of submerchantable hardwood stems, and (3) mortality or severe damage of retained merchantable trees of 1 .O stem per adre for pines and 2.7 stems per acre for hardwoods. Pine regeneration 1 year after harvesting was significantly affected by the seedbed conditions exkting after the harvest. Exposed mineral soil and disturbed litter increased the number of seedlings, while the effects of fine logging slash were negative. INTRODUCTION Most knowledge about the uneven-aged silviculture of loblolly (Pinus taeda L.) and shortleaf (P. echinafa Mill.) pines was accumulated over a 50-year period at the Crossett Experimental Forest in southeastern Arkansas (Reynolds 1959, Reynolds and others 1984). Uneven-aged silviculture was used to rehabilitate understocked, cutover stands that already had somewhat of a reverse-J size-class distribution. Crossett guidelines call for aggressive competition control and periodic harvests to favor pine regeneration and provide acceptable growth and yield rates. Harvesting is one of the principal stand disturbances in uneven-aged stands, and it is the way that stocking of merchantable trees is regulated. Some of the impacts of harvesting benefit stand regeneration, such as creating favorable seedbed and environmental conditions and destroying some of the competing vegetation. However, other effects are harmful, such as damage to both regeneration and merchantable trees. To determine potential disturbance levels from logging uneven-aged stands, we monitored the conditions existing before and after the harvesting operation implementing a study testing uneven-aged silviculture in a pine-hardwood stand. METHODS Study Site The study was installed in a mature, second-growth pine-hardwood stand in the Homochitto National Forest in Franklin County, Mississippi. Soils in the study area are mapped as the Lorman series (Vertic Hapludalfs), which has a silty loam surface horizon and a clayey subsurface. The site is in the Southern Pine Hill physiographic district. Elevations ranged from 200 to 260 ft above sea level. Plots were located on the side slopes in an area of undulating topography, and slopes ranged from 8 to 15 percent. The basal area of merchantable (d.b.h. 23.6 inches) pines averaged 87 I? per acre before harvest, with two-thirds consisting of shortleaf pine and one-third loblolly pine. Basal areas averaged 32 ft2 per acre for merchantable hardwoods. Study Design and Treatment Implementation Eighteen square, 05acre plots were installed and surrounded by a 58.2-R isolation strip that received the same treatment. Treatments reduced merchantable basal area to two levels for pines (45 and 60 ff per acre) and three levels for hardwoods (0, 15, and 30 * per acre). Treatments were assigned in a completely random design with three replications for each pine-hardwood combination. The pine harvest was implemented using the basal-area maximum-diameter quotient technique of singletree selection (Baker and others 1998). Guidelines were for a maximum diameter of 24 inches and a quotient of 1.2 for l-inch d.b.h. classes. Guidelines for maximum diameter and quotient were followed as closely as feasible because the stand lacked a balanced reverse-J structure. Hardwood retention favored the larger and higher quality red and white oaks. The study area was harvested in dry weather during September and early October of 1990. Primary skidtrails were located along the crest of long, narrow ridges that extended through the study area, with secondary skidtrails extending downslope. Because plots were located on the side slopes, trees from one plot were not skidded through another, which isolated the harvesting impacts for individual plots. Loggers used two rubber-tired cable skidders with 120 horsepower engines. Logs were skidded tree-length with no special restrictions imposed. Harvested volume of merchantable pines averaged 998 V per acre and ranged from 0 to 2,400 t? per acre for individual plots. Harvested pine sawtimber averaged 4,140 board ft Doyle per acre. This was a relatively high volume because it was the initial application of uneven-aged silviculture. Harvested volumes in uneven-aged stands on good sites will typically range from 1,200 to 4,000 board ft Doyle per acre depending on the cutting-cycle length (Baker and others 1998). ’ Paper presented at the Tenth Biennial Southern Silvicultural Research Conference, Shreveport, LA, February 16-18, 1999. * Research Forester and Research Forester (deceased), USDA Forest Service, Southern Research Station, Monticello, AR 71656-3516, respectively.