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Timber extraction with crawler tractors in humid tropical forests causes degradation of
soil physical properties and decreases plant growth. We tested rehabilitation of tracks in
a second rotation Acacia mangium plantation in Sabah, Malaysia, by tilling with
additions of NPK-fertilizer, ash and organic material to a depth of 15–20 cm. Two years
after planting total basal area of A. mangium seedlings was 62% higher outside tracks
compared to unimproved tracks, while on NPK-fertilized tracks performance was 700%
higher compared to unimproved tracks. Corresponding figures for average height were
40 and 80%. After 8 days with little rain track topsoil experienced water shortage with
all studied soil improvements. For ‘non-tracked’ areas wilting-point (-1500 kPa) was not
reached during 17 days of dry weather, and more meso-pores were present.
Consequently, depending on rainfall after planting the effect of soil rehabilitation on tree
performance may be less positive than shown here, because dry periods of 2 weeks
length are common in the humid tropics. Bulk density on plots outside tracks in this
second-generation plantation was 60% higher than have been reported in similar first
generation plantations. It is discussed that this might be a warning that repeated
logging and fire may have a detrimental effect on soil physical properties.