Effect of local stand structure on leaf area, growth, and growth efﬁciency following thinning of white spruce Kwadwo Omari a,⇑ , David A. MacLean a , Michael B. Lavigne b , John A. Kershaw Jr. a , Greg W. Adams c a University of New Brunswick, Faculty of Forestry and Environmental Management, P.O. Box 4400, Fredericton, NB E3B 5A3, Canada b Natural Resources Canada, Canadian Forest Service – Atlantic Forestry Centre, Fredericton, NB E3B 5P7, Canada c J.D. Irving, Limited, P.O. Box 5777, 300 Union Street, Saint John, NB E2L 4M3, Canada article info Article history: Received 14 November 2015 Received in revised form 1 March 2016 Accepted 1 March 2016 Keywords: Picea glauca Thinning Area potentially available Leaf area Growth efﬁciency Current annual volume increment abstract We examined the inﬂuence of stand structure surrounding individual dominant and codominant trees on leaf area, tree growth, and growth efﬁciency (stem growth per unit leaf area) in young white spruce (Picea glauca (Moench) Voss) plantations. Objectives were to (i) test the hypothesis that individual tree volume increment and growth efﬁciency increase with increasing growing space, and (ii) determine the relative importance of growth efﬁciency and leaf area to stem volume increment in young spruce following thin- ning. Growing space was expressed as area potentially available (APA) to each tree. Relative current annual volume increment (annual increment divided by the mean increment for the 3 years immediately preceding thinning) increased linearly with increasing APA 2 and 3 years after thinning, supporting our hypothesis that tree volume increment increases with APA. Growth efﬁciency however, was not related to APA. Leaf area was positively related to APA 3 years after thinning, and current annual volume incre- ment was related to leaf area. Leaf area per tree increased from 17.8 m 2 to 29.8 m 2 over the 3 years (2011–2013) following thinning and was 16.5–18.7 m 2 for unthinned trees over the same period. Growth efﬁciency decreased from 1.35 to 0.64 dm 3 m 2 for thinned trees and from 0.74 to 0.55 dm 3 m 2 for unthinned trees from 2010 to 2013. Growth efﬁciency did not differ between thinned and unthinned trees, but it was signiﬁcantly lower in year 3 than year 1 after thinning (p = 0.0178) and signiﬁcantly lower than the prethinning growth efﬁciency (p = 0.0034). Our results show that thinning increased indi- vidual tree volume increment by increasing leaf area of remaining trees and not by increasing their growth efﬁciency. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Tree growth is a function of the amount of foliage, the rate of photosynthesis per unit of foliage, allocation of photosynthate to components and conversion rates to new structural matter (Brix, 1983). The unit leaf area rate or net assimilation rate, i.e. the dry weight increase per unit of foliage over time (Briggs et al., 1920; Evans, 1972), can be used as a surrogate for photosynthesis and conversion rates because these are difﬁcult to measure for entire plants over long periods of time (Brix, 1983). For forestry purposes, growth efﬁciency, deﬁned as stem wood growth per unit of foliage by Waring et al. (1980), can be used instead of net assimilation rate. The amount of foliage is strongly correlated with absorbed photosynthetic active radiation (Binkley et al., 2010; Gspaltl et al., 2013) and can be regarded as the potential production capacity of a tree (Brix, 1983). Growth efﬁciency is a measure of resource use efﬁciency (Brix, 1983; Gspaltl et al., 2013) and tree vigor (Waring et al., 1980). Several studies have reported on the relative importance of leaf area and growth efﬁciency in determining tree growth response to thinning. Average rates of stem growth per tree were 3–8 times greater in thinned than in unthinned balsam ﬁr (Abies balsamea (L.) Mill.) stands, and stem growth was correlated with foliar weight, however, growth efﬁciency of dominant and codominant trees in thinned stands were similar to those of similar trees in unthinned stands (Lavigne, 1988). Over a 7-year period, mean annual stemwood biomass increment was 34% greater for thinned Douglas-ﬁr (Pseudotsuga menziesii (Mirb.) Franco) than unthinned trees, and leaf biomass increased by 0.58 kg year 1 for thinned trees compared to a decrease of 0.03 kg year 1 for unthinned trees (Brix, 1983). Stem growth per unit leaf area was only 14% greater for the thinned than unthinned trees indicating that the major growth response to treatment was caused by an increase in the http://dx.doi.org/10.1016/j.foreco.2016.03.005 0378-1127/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: kwadwo.omari@unb.ca (K. Omari). Forest Ecology and Management 368 (2016) 55–62 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco