Interaction among Machine Traffic, Soil Physical Properties and Loblolly Pine Root Proliferation in a Piedmont Soil

The impact of forwarder traffic on soil physical properties was evaluated on a Gwinnett sandy loam, a commonly found soil of the Piedmont. Soil strength and saturated hydraulic conductivity were significantly altered by forwarder traffic, but reductions in air-filled porosity also occurred. Bulk density did not increase significantly in trafficked treatments. The greatest impacts to soil physical properties occurred in the surface layer. Loblolly pine root proliferation increased in both trafficked and untrafficked treatments but differed in the soil depth at which this occurred. Further investigations are necessary to understand the response of roots to machine traffic. INTRODUCTION The impact of forest machinery on harvested sites traditionally has been gauged by changes in soil physical properties including bulk density, soil strength, macroporosity, saturated hydraulic conductivity, and water infiltration (Gent and Ballard 1984, Greaten and Sands 1980, Lenhard 1986, Reisinger and others 1988, Wronski 1984). Soil physical properties are negatively impacted during trafficking; the results can persist for many years and limit tree productivity (Greaten and Sands 1980, Tuttle and others 1988). Low productivity of selected pine species is correlated with impaired root growth and devejopment in compacted soils. Compaction restricts the volume of soil that can be exploited for available moisture and nutrients (Mitchell and others 1982, Sands and Bowen 1978, Tuttle and others 1988). The relationship among machinery, root systems, and soil physical properties has been extensively investigated in agricultural systems and linked to numerical values of soil physical properties that are considered to be root limiting (Unger and Kaspar 1994). An understanding of this relationship for tree species is limited, and future productivity would be aided by an understanding of soil physical changes and their role in root growth. The objective of the study was an evaluation of the impact of forwarder traffic on selected soil physical properties of a Piedmont soil, and determination of a response by loblolly pine roots to forwarder traffic.