Nitrogen net mineralization and dynamics following whole-tree harvesting and winter windrowing on clayey sites of northwestern Quebec Suzanne Brais a,*,1 , David Pare ´ b,2 , Claude Camire ´ c,3 , Pascal Rochon d,4 , Claire Vasseur e,5 a Universite ´ du Que ´bec en Abitibi-Te ´miscamingue, 445 blv. Unversite ´, Rouyn-Noranda, Que., Canada J9X 5E4 b Canadian Forest Service, 1055, rue du P.E.P.S., Ste-Foy, QC, Canada G1K 7P4 c Centre de recherche en biologie forestie `re, Universite ´ Laval, Ste-Foy, QC, Canada G1K 7P4 d Groupe de recherche en e ´cologie forestie `re, UQAM, Montre ´al, QC, Canada H3C 3P8 e Biodo ˆme de Montre ´al, 4777 Av. Pierre de Coubertin, Montre ´al, QC, Canada H1V 1B3 Received 7 June 2000; accepted 30 October 2000 Abstract Concerns over decreases in soil nitrogen reserves and productivity following the removal of logging residues (windrowing, shearblading and piling) have been raised by numerous researchers. Medium-term impacts of this practice on soil N reserves and availability and on indices of organic matter quality were assessed for balsam fire (Abies balsamea (L.) Mill.), white birch (Betula paperyfera Marsh.) and white spruce (Picea glauca (Moench) Voss) stands growing on dry to fresh clayey sites in northwestern Quebec, Canada. Unharvested control stands, whole-tree harvested cutovers and windrowed sites were compared. Fifteen years following harvesting and windrowing, forest floor Kjeldahl N concentrations and content and forest floor in situ net N mineralization rates (undisturbed closed top cores incubation) were affected by harvesting but not by windrowing. No differences in mineralization constant, potentially mineralizable N and cumulative mineralized N (526 day incubation period) were found between treatments, suggesting that treatment differences in field net N mineralization rates were the result of interactions between residual ecosystem structures such as forest floor, coarse woody debris and vegetation and meteorological conditions. If these trends persist over time, it could signal that, while whole-tree harvesting does not have a direct effect on soil organic matter quality, long-term impacts on N dynamics could result from changes in ecosystem structures. Slash removal following whole-tree harvesting did not have any additional negative impact. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Whole-tree harvesting; Winter windrowing; Shear and pile; Nutrient pools; Nitrogen net mineralization; Organic matter quality; Boreal forest 1. Introduction Windrowing or shear piling is a common practice used to prepare cutovers prior to plantation establish- ment (Pye and Vitousek, 1985; Powers et al., 1988; Dyck and Skinner, 1990). In windrowing, slash, resi- dual vegetation and sometimes, portions of the forest Forest Ecology and Management 157 (2002) 119–130 * Corresponding author. E-mail addresses: suzanne.brais@uqat.uquebec.ca (S. Brais), dpare@cfl.forestry.ca (D. Pare ´), claude.camire@sbf.ulaval.ca (C. Camire ´), rochon.pascal@uqam.ca (P. Rochon), c_vasseur@ville.montreal.qc (C. Vasseur). 1 Tel.: þ819-762-0971, ext. 2349. 2 Tel.: þ418-648-7598. 3 Tel.: þ418-656-2131, ext. 7773. 4 Tel.: þ514-987-6531. 5 Tel.: þ514-868-3095. 0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-1127(00)00643-5