Harvesting intensity at clear-felling in the boreal forest:: Impact on soil and foliar nutrient status

The amount of logging residues left on site after clear-felling has been shown to influence the state of soil nutrient resources, but this effect may depend on soil conditions. In three regions of the boreal zone of Quebec, with contrasting soil characteristics, soil and foliar nutrient status of young (15-20 yr old) stands were compared among sites that were clear-felled at two harvesting intensities, that is, stem-only (SOH) and whole-tree harvesting (WTH). Balsam fir (Abies balsamea) stands were studied in the For (e) over capt Montmorency and Gaspesie regions, while black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) were studied in the Haute-Mauricie region. Whole-tree harvesting resulted in lower cation exchange capacity (CEC) compared with SOH, but this effect could be linked to decreased levels of organic C only in the Haute-Mauricie region, where soils had intrinsically low organic matter content. Lower soil and foliar Ca concentrations after WTH were observed in all three regions. Foliar Ca status was most strongly affected by harvesting intensity in Gaspesie, where soils exhibited the lowest concentration of total Ca in the parent material. In Haute-Mauricie, where the parent material contained a low level of Mg, foliar nutrition for this element was significantly poorer under WTH compared with SOH. Harvesting intensity did not influence the biogeochemical cycles of K and N. Foliar analysis revealed that jack pine exhibits the strongest nutritional difference between WTH and SOH. Results suggested that the tree species regenerating the harvested sites, as well as the total Ca and Mg contents of the parent material are better indicators of a site's susceptibility to nutritional alteration by WTH than soil available nutrient status.