Growth and physiological response of eastern white pine seedlings to partial cutting and site preparation Jean-Franc ¸ois Boucher a, * , Pierre Y. Bernier b,1 , Hank A. Margolis a,2 , Alison D. Munson a,3 a Centre de Recherche en Biologie Forestie `re, Pavillon Abitibi-Price, Universite ´ Laval, Que ´bec (Qc), G1K 7P4, Canada b Laurentian Forestry Centre, Canadian Forest Service, P.O. 10380, Sainte-Foy (Qc), G1V 4C7, Canada Received 29 July 2006; received in revised form 19 December 2006; accepted 20 December 2006 Abstract We examined how white pine (Pinus strobus L.) seedlings planted under a mature cover of white and red (Pinus resinosa Ait.) pine in eastern Ontario (Canada) responded to treatments aimed at improving light and soil conditions for seedling growth. The treatments were: (a) three levels of partial cutting (no cut or CS0, cut to one-crown spacing between residual trees or CS1, cut to two-crown spacing or CS2); (b) two levels of vegetation control (without herbicide or H0, with herbicide or H1); and (c) two levels of soil scarification (S0 and S1). On the third growing season after planting, total growth of seedlings was lowest in CS0 treatment and similar in CS1 and CS2 treatments. The CS2 created better growing light conditions than the CS1, with and average of 50% of full light at seedling height, which corresponded to the maximum height and diameter growth rates of seedlings. However, CS2 also stimulated the growth of competing woody vegetation (both understory trees and shrubs), and resulted in greater microsite heterogeneity of light availability. Scarification warmed the soil (approximately 1–3 8C in the middle of the growing season), decreased the density of competing trees, but increased the shrub density, with no impact on white pine seedling growth. The treatments had no effect on light-saturated photosynthetic rate (A) of current-year foliage of seedlings, nor on their midday shoot water potential. Leaf N was higher in partial cuts and with vegetation control, but the relationship between N and A was weak to non-existent for the different foliage classes. Measures of the proportion of aboveground biomass allocated to foliage (leaf-mass ratio) suggest an acclimation response of young white pine that improves growth under moderate light availability and compensates for the lack of leaf-level photosynthetic plasticity. We suggest a combination of soil scarification under a one-crown spacing partial cut (corresponding to 14 m 2 ha 1 of residual basal area, or an average of 32% of available light at seedling height) as an establishment cut. This should provide optimum growth conditions for planted understory white pine, while also favoring natural regeneration and providing some protection against damage from insects and disease. # 2007 Elsevier B.V. All rights reserved. Keywords: Shelterwood system; Pinus strobus; Partial cutting; Site preparation; Competing vegetation; Biomass allocation; Gas exchange; Water relations; Acclimation 1. Introduction Extensive exploitation of eastern white pine (Pinus strobus L.) in northeastern North America during the last two centuries dramatically reduced both the number and quality of white pine forests (Aird, 1985; Kershaw, 1993). Attempts to renew the species initially focused on artificial regeneration. However, planting after clearcutting or on abandoned farm land has generally been unsuccessful because of the vulnerability of white pine to two major pests in open conditions: white pine weevil (Pissodes strobi (Peck)) and blister rust (Cronartium ribicola J.C. Fisch.) (Kershaw, 1993; Krueger and Puettmann, 2004). Consequently, the shelterwood system is now frequently www.elsevier.com/locate/foreco Forest Ecology and Management 240 (2007) 151–164 * Corresponding author. Present address: Universite ´ du Que ´bec a ` Chicoutimi, De ´partement des Sciences Fondamentales, 555, Boul. de l’Universite ´, Chicou- timi, Que ´bec (Qc), G7H 2B1, Canada. Tel.: +1 418 545 5011x5385; fax: +1 418 545 5012. E-mail addresses: jean-francois_boucher@uqac.ca (J.-F. Boucher), pbernier@cfl.forestry.ca (P.Y. Bernier), hank.margolis@sbf.ulaval.ca (H.A. Margolis), alison.munson@sbf.ulaval.ca (A.D. Munson). 1 Tel.: +1 418 648 4524; fax: +1 418 648 5849. 2 Tel.: +1 418 656 7120; fax: +1 418 656 5262. 3 Tel.: +1 418 656 7669; fax: +1 418 656 5262. 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.12.020