Impacts of soil compaction persist 30 years after logging operations in the Amazon Basin

Abstract

This study was conducted in a humid tropical forest located in Brazil within the Amazon Basin on a heavy clay Ferralsol 24 and 30 years after logging to evaluate the recovery process of skid trails. All timber was extracted with a D6 track-type tractor. In total, four skid trails were evaluated, all logged in 1987 and two of them again in 1993. Systematic sampling was applied to the four trails and two controls. The data collected were rut depth, soil bulk density (BD), soil penetration resistance (PR) and seedling and sapling density. Soil physical properties were determined in three layers from 0 to 15 cm in depth, and seedling density was determined from 36 plots of 4m² in size at the soil sample locations. Rut depths were significantly different (p < 0.05) between years, with the greatest depth of 32 cm recorded for the soil in 1993. The results for BD and PR differed from each other only slightly. In the 0–5 cm depth between the ruts both BD and PR were still significantly higher (p < 0.05) than the control for both years, but within the ruts there were no significant differences between the controls of either year. However, in the 5–15 cm depth within the ruts, BD was always significantly higher (p < 0.001) than the control for both years, as well as was PR for the depths 5–10 cm (p < 0.05) and 10–15 (p < 0.001) within the ruts for both years. The soil layers between the ruts in the depth of 10–15 cm for 1993 were significantly different (p < 0.05) for BD and PR, but the means for this same depth were not root limiting for plants for either BD or PR. The evaluation of seedling and sapling density revealed significant differences for the class of saplings greater than 150 cm. Both the 1987 and the 1993 plots had significantly lower numbers per m², 1987 (p < 0.01) and 1993 (p < 0.001), than the control. There were more saplings located between the ruts than in the ruts for both years, but this was not statistically significant. The conclusion of this study is that partial recovery of the disturbed soil had occurred after 24 and 30 years, with the soil surface horizon within the ruts no different than the undisturbed soil of the control. However, the results show that even 30 years is not sufficient for a full recovery of the soil. © 2019 Elsevier B.V.