Wheel traffic influence on poplar regeneration and grass yield

All transport in forest stands occurs on the ground that at the same time is used as a growth substrate, not only for timber production but for grass as well in several Argentine production systems. Heavy traffic will damage the ground vegetation, affect tree roots and compact the soil to a degree where the tree roots have difficulty in regenerating in the damaged zone. The main objective of this research was to evaluate changes in soil compaction, introduced by traffic, during harvesting operations in a timber forest where grass production is also used for cattle feeding. Four experimental variables were measured: changes in bulk density in the profile, changes in penetration resistance, grassland yield and forest plantation regeneration after harvesting traffic. The work was performed in the south of the Rolling Pampa region, Argentina. The soil was a fine clayey, illitic, thermic Typic Argiudoll. Treatments consisted of four different traffic intensities, due to different passes of a tractor pulling a trailer on the inter-row area of the plantation, during harvesting operations. Increasing the number of traffic passes, increased the depth at which differences in cone penetration resistance values began to be significantly higher. The increments in bulk density values after traffic were not so evident as those in penetration resistance values, but the same tendencies were shown. The least traffic intensity, corresponding to only one pass, resulted in a reduction of grass yield (40-3%) in comparison with the control (no traffic) treatment, although there was no effect on tree regeneration. Traffic within the plantation impacted principally on tree shoot mortality, with a maximum of 51.5%, measured 1 year after traffic, recorded in the ten pass treatment. Grassland production within the plantation, after harvesting operations, was directly associated with forest regrowth. (C) 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.