Total foliar area and average leaf age may be more strongly associated with branching frequency than with leaf longevity in temperate conifers

Summary•  Average canopy needle age (Λ M ) is an important plant characteristic determining canopy carbon gain potential. We developed a demographic model, suggesting that Λ M depends on needle maximum age (Λ max ), but also on the production rate of foliage. We studied Λ max , shoot growth and branching in three conifers to disentangle the contrasting controls on Λ M . •  Abies balsamea had a Λ max of up to 16 yr, Picea abies up to 12 yr, and Pinus sylvestris up to 6 yr. Increases in branch irradiance were associated with increases in shoot length, more frequent branching, increases in the asymmetry and peakedness of shoot length distributions, and decreases in Λ max and Λ M . Our model and experimental data suggested that higher Λ M at lower irradiance resulted both from increases in Λ max and decreases in branching and extension growth in the shaded branches. •  Significance of various determinants of Λ M was species‐dependent, and varied with needle survivorship curves and shoot bifurcation ratio. •  Our study demonstrates that total foliar area and average age may be more strongly associated with branching frequency than with leaf longevity.