Cumulative management impacts on soil physical properties and early growthof Pinus radiata

Effects of Pinus radiata D. Don plantation management on soil physical prop erties and second rotation (2R) tree growth were quantified for a site cons idered by managers as resistant to compaction. Measurements commenced prior to clearfall and were repeated following harvest and again at 2 and 4 year s after second rotation establishment. Effects of earlier thinning on soil physical properties detected prior to clearfall were found to influence the degree of soil change caused during clearfall. Bulk density and soil stren gth measurements showed that harvesting caused Light to moderate compaction of almost 80% of the study area. Moderate compaction over 25% of the area was associated with visible rutting (RUTS class) whilst a lower level of co mpaction occurred over 54% of the area where visual evidence was minimal (L OW class). Subsoiling of planting lines for second rotation establishment c aused a major reduction in penetration soil strength to 0.45 m depth. This effect was still pronounced at 4 years of age. Outside subsoiled areas it w as still possible to detect statistically significant compaction in the RUT S class at 2 years of age but not in the LOW class. By 4 years of age, comp action in the RUTS class had declined relative to the LOW class and was no longer detectable in comparison with pre-harvest values. Tree growth at age 2 years was not significantly different between the two dominant disturban ce classes although there was slight evidence of a compaction effect. By ag e 4 years there were no differences in height or volume index between the t wo disturbance classes. A slash residue-piled-and-burnt site preparation tr eatment resulted in significantly greater tree volume index at age 2 years. This response was still apparent, but at a diminished level, by age 4 year s. The response was assumed to be due to nutrient effects as soil physical properties were not significantly different between the two treatments. Alt hough moderate compaction had occurred across the site, there was no effect on the growth of young P. radiata that would be of immediate concern for s ite productivity. (C) 2000 Elsevier Science B.V. All rights reserved.