How do forest harvesting methods compare with wildfire? A case study of soil chemistry and tree nutrition in the boreal forest Evelyne Thiffault, Nicolas Be ´ langer, David Pare ´ , and Alison D. Munson Abstract: An important tenet of the natural disturbance paradigm as a basis for sustainable forest management is that im- pacts of interventions fall within the range of natural variation observed for the disturbance in question. We evaluated differ- ences in soil nutrients, soil acid–base status, and tree nutrition between two harvesting methods (whole-tree (WTH) and stem-only (SOH)) and wildfire, 15–20 years after disturbance, to assess whether these harvesting methods have biogeochem- ical impacts that are within the natural range of variation caused by wildfires in boreal coniferous stands of Haute-Mauricie (Quebec). Both SOH and WTH created conditions of forest floor effective cation-exchange capacity, exchangeable Ca and K concentrations, base saturation, Ca:Al molar ratio, and organic C concentrations that were lower than the range of values for wildfires. We hypothesize that the immediate deposition of soluble base cations and the incorporation of recalcitrant or- ganic matter that characterize wildfires generate biogeochemical conditions that are not emulated by either harvesting method. The improved soil nutritional environment after wildfire compared with SOH and WTH was reflected in jack pine (Pinus banksiana Lamb.) foliar nutrient composition but not in black spruce (Picea mariana (Mill.) BSP) foliage. The re- sults raise uncertainties about the long-term base nutrient availability of the harvested sites on Boreal Shield soils. Re ´sume ´: L’un des principes importants du paradigme sur les perturbations naturelles en tant que base de l’ame ´nagement forestier durable est que les impacts des interventions humaines doivent respecter la gamme de variation cre ´e ´e par les per- turbations naturelles. Nous avons e ´value ´, 15 a ` 20 ans apre `s perturbation, les diffe ´rences entre deux proce ´de ´s de re ´colte (coupe par arbre entier et coupe par tronc entier) et des feux de fore ˆt quant a ` leurs effets sur les e ´le ´ments nutritifs et le statut d’acidite ´–alcalinite ´ du sol, ainsi que sur la nutrition des arbres. Nous voulions juger dans quelle mesure les impacts bioge ´ochimiques des proce ´de ´s de re ´colte sont dans la gamme naturelle de variation cre ´e ´e par les incendies de fore ˆt dans des peuplements conife ´riens bore ´aux de la Haute-Mauricie (Que ´bec). Les deux proce ´de ´s de re ´colte ont cre ´e ´ dans la cou- verture morte des conditions de capacite ´ d’e ´change cationique effective, de concentrations en Ca et K e ´changeables, de saturation en bases, de ratio molaire Ca:Al et de concentration en C organique qui e ´taient infe ´rieures a ` la gamme de va- leurs mesure ´es dans les sites de feu. Nous e ´mettons l’hypothe `se que le de ´po ˆt soudain de cations basiques solubles et l’in- corporation de matie `re organique re ´calcitrante qui caracte ´risent les incendies forestiers ge ´ne `rent des conditions bioge ´ochimiques qui ne peuvent e ˆtre imite ´es par aucun des proce ´de ´s de re ´colte. L’environnement nutritionnel plus favor- able dans les sites de feu par rapport aux sites de coupe s’est refle ´te ´ dans la nutrition foliaire du pin gris (Pinus banksiana Lamb.), mais non dans celle de l’e ´pinette noire (Picea mariana (Mill.) BSP). Les re ´sultats soule `vent des incertitudes quant a ` la disponibilite ´a ` long terme des cations basiques dans le sol des sites du bouclier bore ´al qui sont soumis a ` la re ´colte. Introduction An important tenet of sustainable forest management is the correspondence between the ecological impacts of har- vesting practices and natural disturbances (Wei et al. 2003). Because fire is the major natural disturbance in the boreal forest of Canada (Weber and Flannigan 1997), it is often used as a benchmark for evaluating the impacts of anthropo- genic disturbances such as clearcutting. The rationale behind this is that the survival, recovery, and productivity of boreal forested ecosystems have evolved in response to wildfire and are therefore well adapted to the conditions created by this type of disturbance (Hunter 1993). To develop and improve natural disturbance-based models of forest management, many studies have documented the periodicity and spatial patterns associated with wildfire (e.g., Bergeron et al. 2002). However, there is more to emu- lating fire than disturbance size, spatiality, and interval of return (McRae et al. 2001). In general, our ability to observe and measure spatial structures is ahead of our understanding of their roles (Spies 1998), and mimicking them, although appealing in simplicity, sidetracks the necessity to deepen the analyses of anthropogenic impacts on ecological proc- esses. For example, at the stand scale, the partial or com- plete burning of trees and forest floor by fire as well as the presence of charred and decayed material remaining on site Received 26 May 2006. Accepted 8 February 2007. Published on the NRC Research Press Web site at cjfr.nrc.ca on 17 September 2007. E. Thiffault and A.D. Munson. 1 Centre d’e ´tude de la fore ˆt, Universite ´ Laval, Que ´bec, QC G1K 7P4, Canada. N. Be ´langer. Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada. D. Pare ´. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., P.O. Box 10380, Stn. Sainte-Foy, Que ´bec, QC G1V 4C7, Canada. 1 Corresponding author (e-mail: alison.munson@sbf.ulaval.ca). 1658 Can. J. For. Res. 37: 1658–1668 (2007) doi:10.1139/X07-031 # 2007 NRC Canada