Application of Gps Technology to Monitor Traffic Intensity and Soil Impacts in a Forest Harvest Operation’

A study was initiated in the Winter of 1998 to examine the utility of employing Global Positioning Systems (GPS) to monitor harvest traffic throughout a loblolly pine plantation and utilize traffic intensity information to assess impacts of select soil physical properties. Traffic maps prepared from GPS positional data indicated the highest concentration of traffic intensities occurred in the landings and skid trails (11 or more) while approximately 94 percent of the site was subjected to 10 or less passes. Estimates of bulk density and gravimetric water content did not approach levels in any traffic intensity class considered to be restrictive to root penetration for either surface or subsurface layers. Soil strength levels for each traffic intensity dass in the surface layer did not indicate the presence of an impenetrable layer but subsoil modification may be necessary to provide a proper environment for regeneration. INTRODUCTION Mechanized forest harvest operations can alter soil physical properties which have the potential to influence subsequent management prescriptions and future forest productivity and soil sustainability. In the past, critical information on trafficking damage has relied on the tabulation of subjective surface disturbance classes. the measurement of changes in soil physical properties or a combination of the two methods. Both methods are hampered by the significant amount of time and labor required to implement them and the lack of accu:acy required to truly estimate soii disturbance and soil compac!ion. Global Positioning Systems (GPS) have been employed recently in numerous forestry activities including utilization in thinning& tracking movements of site preparation equipment, and locating soil disturbances related to harvest activities (McMahon 1997; Stjernberg 1997; Thor and others 1997). Recent studies have evaluated GPS systems and data to depict traffic maps of intensities, or the number of traffic passes to which a ground area of specific dimension has been subjected, and their distribution (McDonald and others 1998b; 1998c; McMahon 1997). Knowledge of the location of traffic intensities and their geographic distribution in a harvested landscape has the potential to provide a means of evaluating soil physical response to trafficking (Carter and McDonald 1998). Linking traffic damage to soil response may provide a framework for future decision making in application of site preparation and prediction of regeneration po ten t ia l . OBJECTIVE The study was conducted in a loblolly pine plantation in the Piedmont region of Alabama with the following objectives: (I) the evaluation of GPS technology to monitor trafficking patterns and intensities, (2) measurement of the response of select soil physical properties to trafficking, and (3) correlatiQn of soil changes to harvest traffic intensities. MATERIALS A N D METHODS Site Characteristics The study site was located in a 20-year-old loblolly pine (Pinus taeda L.) plantation, approximately 25.4 hectares in size, in Lee County, Alabama. Tree basal area was estimated to be 120 f? per acre of loblolly pine and 20 fY of hardwood with an expected yield of 90 green tons per acre. Soils within the harvest tract were primarily classified as clayey, kaolinitic, thermic members of the Typic Rhodudults (U.S. Department of Agriculture, Soil Conservation Service 1975). Two slope phases of the Gwinnett series were present within the portions of the harvest tract under evaluat ion. Harvest and Global Positioning Systems The harvest system configuration consisted of a single feller buncher (liydroax 5 11 E), two grapple skidders (Timberjack 460D and 450C) pulling to two separate decks, and two loaders (Prentice 270) located at each deck and equipped wi th an in tegra ted delimber/slasher. Product ion averaged approximately seven to eight loads per day. Global Positioning System data wascollected by means of two.types of GPS receivers: a Trimble ProXR and Trimble GeoExplorer. The final GPS and harvest system configuration consisted of the GeoExplorer mounted on the feller-buncher and two ProXrs mounted on each skidder. Data were collected in 2-sec&nd increments throtighout the harvest day, differentially corrected in the iaboratory, and exported to a GIS based system for editing. Detailed information on the transformation of vector based data into raster based maps used in this study has been previously pub l ished (McDonald and o thers 1998a) . Soil Physical Properties The impact of traffic intensity on soil response was assessed by evaluating soil physical properties at select point locations corresponding to a specific traffic intensity. The relationship between soil physical response and traffic intensity was determined by fixing a ground position by GPS, matching coordinates to traffic maps and by collecting soil samples from these locations. A grid approximately 60 x 73 m in size (-0.4 ha) was established and soil physical data collected in situ or by removal of soil cores at each point. Soil strength was measured on a 3x 6-m grid and soil bulk density and gravimetric water content evaluated on a 6x 6m grid basis. Soil penetrometer data was collected by a Rimik CP20 recording cone penetrometer to a depth of ’ Paper presented at the Tenth Biennial Southern Silvicultural Research Conference, Shreveport, LA, February 16-18, 1999. ’ Research Soil Scientist and Research Engineer, USDA Forest Service. Southern Research Station, Auburn. AL 36849; and Research Supervisor, Mead Coated Board, Phenix City. AL 36868, respectively.