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

Abstract

Summary • Average canopy needle age (ΛM) is an important plant characteristic determining canopy carbon gain potential. We developed a demographic model, suggesting that ΛM depends on needle maximum age (Λmax), but also on the production rate of foliage. We studied Λmax, shoot growth and branching in three conifers to disentangle the contrasting controls on ΛM. • Abies balsamea had a Λmax 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 Λmax and ΛM. Our model and experimental data suggested that higher ΛM at lower irradiance resulted both from increases in Λmax and decreases in branching and extension growth in the shaded branches. • Significance of various determinants of ΛM 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.