The role of tree uprooting in Cambisol development

The role of tree uprooting in soil formation was studied in a natural forest in a Cambisol soil zone on both the fine pit-mound spatial scale and on the coarse forest ecosystem scale. The effect of a lack of pit-mound dynamics in managed forests was also assessed.Properties of pit-mounds were studied in a 10.8 ha plot. From a total of 1562 pit-mounds, a representative sample of 51 was chosen for dendrochronological dating. Ages were determined to be between 9 and 191 years. The development of soils was studied for 14 pit-mounds of all ages. A total of 210 samples were taken from microsites at mounds, pits, and currently non-disturbed ground, from the depths 0–10, 15, 30, 50 and 100 cm. In addition, samples were taken from 9 profiles in managed forests in which tree uprooting dynamics have been prevented for at least 200 years (45 samples). Each sample was analyzed for 38 chemical and physical soil characteristics. Multidimensional statistical methods were used to evaluate the significance of (i) sampling depth, (ii) microsite, and (iii) age since the last disturbance on soil properties in the natural forest. Depth explained 12.1% of the variability in soil characteristics (p < 0.001), while microsite and age explained 7.5% (p < 0.001) and 1.8% (p = 0.048) of the variability, respectively. The highest values of Ca, Mg, C and CEC were found in pits, whereas mounds had the highest values of labile Al and exchangeable acidity. Currently non-disturbed soils had values close to the average between mound and pit values. Despite generally higher values of sorption complex characteristics, pits showed leaching of the sorption complex, leaching of C and mild clay illuviation up to about 100 years of age. Mounds showed increasing CEC values over time, as well as an increasing proportion of humic acids, with significant changes in the proportions of Fe (and Al, Si) forms. Some soil characteristics had a unimodal time course.Unlike the natural forest, the managed forest soils had considerably higher contents of the crystalline forms of Fe, Al and Mn, reflecting a more advanced stage of soil formation. However, the different disturbance regimes did not affect the course of clay illuviation, sorption complex leaching, or the content of organic matter.

Research highlights
► Pit-mound microsites showed different state and development of soils over time.
► Microsites showed changes in the proportions of Fe, Al, Mn, Si forms over time.
► Some soil characteristics had a unimodal time course.
► The managed forest soils had a more advanced stage of soil formation.