Effect of local stand structure on leaf area, growth, and growth efficiency following thinning of white spruce

• We studied influence of stand structure on thinning response in spruce plantations.
• Growing space was expressed as area potentially available to each tree.
• Leaf area was related to growing space but growth efficiency was not related.
• Tree growth increased with growing space and was positively related to leaf area.
• Thinning increased tree growth by increasing leaf area and not growth efficiency.

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 thinning. 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 increment was related to leaf area. Leaf area per tree increased from 17.8 m2 to 29.8 m2 over the 3 years (2011–2013) following thinning and was 16.5–18.7 m2 for unthinned trees over the same period. Growth efficiency decreased from 1.35 to 0.64 dm3 m−2 for thinned trees and from 0.74 to 0.55 dm3 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 individual tree volume increment by increasing leaf area of remaining trees and not by increasing their growth efficiency.