Canadian Forest Service Publications
Long-term soil response to variable-retention harvesting in the EMEND (Ecosystem Management Emulating Natural Disturbance) experiment, northwestern Alberta. 2014. Kishchuk, B.E.; Quideau, S.; Wang, Y.; Prescott, C. Canadian Journal of Soil Science 94(3):263-279.
Issued by: Northern Forestry Centre
Catalog ID: 35618
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We report on soil responses to variable-retention (VR) harvesting from a large-scale experiment (>1000 ha). Samples were taken prior to treatment, and 1 and 6 yr after treatment under cover types representing the successional trajectory for boreal mixedwood forests in northwestern Alberta, Canada. Variable-retention harvesting at six overstory-retention levels [100 (control), 75, 50, 20, 10, and 0% (clearcut)] were applied to 10-ha experimental units under four cover types: deciduous-dominated (80-95% trembling aspen); deciduous-dominated with coniferous understory (80-95% trembling aspen with white spruce understory at 60-80% of full stocking); mixed coniferous-deciduous (35-65% of each); and coniferous-dominated (80-95% white spruce). Only a few clear differences in soil properties attributable to VR harvesting were evident 6 yr post-harvest: (1) both extractable NH4-N in forest floor and 0-7 cm mineral-soil, and forest floor exchangeable K decreased with increasing canopy removal, and (2) forest floor exchangeable Ca increased with canopy removal. There was a decreasing trend in forest floor and mineral soil C (kg ha-1</sup/>) in undisturbed stands between 1998 and 2005. Differences in soil properties among cover types included higher pH and N concentration in forest floors, and higher cation exchange capacity and exchangeable Ca and Mg in mineral soils in deciduous-dominated stands. Deciduous-dominated stands appear to have distinct soil properties that change under stand development.
Plain Language Summary
This research identified the soil properties most subject to change under six harvesting levels that progressively removed greater amounts of the forest cover (variable retention harvesting). The harvesting treatments were each applied in four different dominant tree cover types of the western boreal mixedwood forest. Changes due to forest harvesting were compared against a pre-harvest baseline one year and six years after harvesting, over a 720-ha experimental area. Six years after harvesting, changes in soil nutrients due to harvesting were limited to extractable ammonium-nitrogen, and exchangeable potassium and calcium. There were, however, clear differences in soil properties due to the dominant tree cover type. Stands containing only deciduous trees had soil properties that were different from stands containing coniferous trees (coniferous dominant stands and mixed stands), which are at a later successional stage. Soil properties such as soil organic matter, nitrogen, soil pH, exchangeable cations, and cation exchange capacity were most influenced by dominant tree cover type. The results indicate that soil properties in these western boreal mixedwood stands are inherently influenced by dominant tree cover type. Alternative management practices such as variable retention harvesting may not alter or influence the naturally occurring successional changes to soils over the time period measured here.