Middle-term effects after timber harvesting with heavy machinery on a fine-textured forest soil

Abstract

Global competition in timber market leads to intensive mechanization of harvesting processes. Consequently heavy equipment is needed, which induces tremendous soil stresses, resulting in severe compaction and degradation of top- and subsoils, especially under moist conditions. Under these circumstances, it is still doubtful that natural processes are able to regenerate the impairments of a harmed forest soil. To test this hypothesis, a long-term field plot has been established in 2003 in Rhineland-Palatinate (Western Germany) on a silty clay loam Cambisol, combined with a measurement of the initial effects of mechanized timber logging on soil properties. Therefore, harvesting operations with a conventional heavy wood-loaded forwarder (Ponsse Caribou; total mass: 22 tons; maximum wheel load: 3.9 tons) were simulated to carry out two treatments with different driving intensities (1 pass, 5 passes). In 2013, analyses were reiterated (focusing on soil physical properties) to estimate the recovery status after a 10 year time span. The results reveal that the structural deformations associated with harmful effects on topsoil and subsoil, caused by wheeling, are still present. A slight regeneration can be considered for the low passing frequency, whereas the higher trafficked forest soil seems to be irreversibly damaged. It is to be expected that these adverse effects will never be fully recovered by natural regeneration.

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