Technical Bulletins & Special Reports

Technical Bulletin No. 0887: Effects of Heavy Equipment on Physical Properties of Soils and on Long-Term Productivity: A Review of Literature and Current Research

Soil disturbance caused by heavy equipment used for harvesting or site preparation can have negative effects on soil properties and long-term forest site productivity. Soil compaction, churning, rutting, mixing, displacement, and removal are types of disturbance that can reduce tree root growth through their influence on soil physical, chemical, and biological properties. Removal or displacement of surface soil can also expose deeper subsoil, which may be less suitable for root growth due to its greater bulk density and soil strength.

Most information on the effects of soil disturbance on root growth is derived from studies of agricultural crops under carefully controlled laboratory and greenhouse conditions. In contrast, trees are long-lived and have great capacity to adapt to restrictive soil conditions through morphological and distributional changes in their root system. This adaptive capacity limits our ability to predict how trees will respond to soil compaction under field conditions. In most soils, compaction reduces subsequent root growth in direct proportion to the degree of compaction. The long-term significance of observed short-term reductions in growth will depend on whether reduced root growth is associated with a) an overall reduction in rootable soil volume and quality or b) simply a slower exploitation of the pre-disturbance rooting volume.

The likelihood or severity of growth impairment from soil disturbance is difficult to generalize because disturbance influences or interacts with other site-specific, growth-determining factors. In most situations, short-term growth of seedlings or saplings on skid trails is less than on adjacent non-skid trail areas; this may or may not reduce ultimate stand yield. Soil disturbance can also have unanticipated secondary effects on tree growth.