Impacts and recovery after soil compaction from logging machinery in Central Amazonia

Abstract

Each year, vast areas of old-growth tropical forest are logged throughout Amazonia. Often, the timber is extracted with heavy machinery, which inadvertently leads to soil compaction. Currently, the majority of research on this topic has been conducted in temperate forests. In the tropics, there is an overall scarcity of research on logging induced soil compaction, especially in the Amazon biome. Therefore, the aim of this work was to quantify the initial impacts and subsequent recovery of soil disturbed by logging machinery in the Central Amazon. Sampling occurred in skid trails, experimental tractor trails, log landings and adjacent undisturbed controls on soil dominated by low activity clay. The experimental trails were established with a D6 track-type tractor to test the differences in soil compaction between seasons (e.g., wet, dry) and traffic intensity (e.g., 1, 3, 12 machine cycles). Time since compaction events ranged from less than a year to 1, 13, 19, 23, 26, 27 and 28 years after soil disturbance. Samples were collected for the following attributes: soil bulk density, soil penetration resistance, fine root biomass, forest floor litter, foliar nutrients (total N, P, K, Ca, Mg, Fe, Mn, Zn) and soil chemical properties (total N, NH4+, NO3-, available P, K+, Ca2+, Mg2+, Na+, Fe2+, Mn2+, Zn2+, Al3+, organic C, pH, cation exchange capacity, base saturation, aluminum saturation). Regardless of season, the first machine cycle caused the greatest increase in soil compaction. There was less damage to macroporosity in the wet season when soil water was above field capacity. At 1 year after compaction, tractor trail soil chemical properties were most affected by heavy compaction in the wet season. Over time, soil recovery occurred at approximately 15 years for cation exchange capacity, 20 years for soil organic C and 25 years for soil bulk density. By 27 after logging, log landings still had not recovered the soil physical properties of fine root biomass encountered in adjacent undisturbed old-growth forest. After 28 years, recovered topsoil in skid trails was still affected by the compacted soil layer below that acted as a hardpan. These findings indicate that impacts from logging machinery are immediate and long-lasting. Therefore, the implications for forest management are to minimize to the greatest extent feasible the construction of logging infrastructure such as skid trails and log landings and plan their layout for future reuse.