Impact of major snig tracks on the productivity of wet eucalypt forest in Tasmania measured 17–23 years after harvesting

Abstract

Summary During ground-based harvesting operations the passage of machinery leads to the formation of a mosaic of major and minor snig tracks from tree stumps to the landing. The impact of heavy traffic can lead to significant changes in the underlying soil physical properties and potentially in long-term growth of trees on these tracks. This study examined the impact of major snig tracks on the productivity of wet eucalypt forest in Tasmania. The three stands studied were dominated by Eucalyptus obliqua that regenerated from clearfelling, slash burning and aerial sowing 17–23 y earlier. Accumulated tree growth and soil physical and chemical properties were measured in three zones: snig tracks, transitional zone (edge of snig tracks), and control. There was a dramatic decline of 52– 80% in the accumulated tree volume in snig track zones when compared to the control zones. This was accompanied by a significant increase in the soil bulk density of 20–23%, and measured changes in a number of soil properties including 22– 33% decrease in organic carbon, 28–32% decrease in total N, and 3–11% decrease in total P on the snig track zones. There was no significant difference in either the soil physical or chemical properties of the transitional zones compared to the control zones, but there was a significant increase in tree growth in the transitional zones, ranging from 30% to 100%. An increase in stand density was the major factor contributing to improved growth in transitional zones, with increases in average diameter and average height having minimal effect. After 17–23 y the increase in stand productivity in the transitional zone compensated for much of the productivity lost due to poor growth on the snig tracks. The overall negative impact of snig tracks on stand productivity was calculated to be of the order of 2–3%.