Estimation of fertility variation in forest tree populations

Forecasts of the effects of tree breeding and conservation operations require information on fertility variation. In most cases, however, the information does not exist or is highly unreliable. In this paper, published studies on flowering abundance, fruit and seed production were used to estimate and review fertility variation in 99 stands and 36 seed orchards. Fertility variations were described by the coefficient of variation (CV) and the sibling coefficient (Ψ). Both measures express how parents differ in fertility; the former focuses on the variance of fertility among individuals while the later focuses on probabilistic aspects. As expected, fertility varied considerably within and among populations. Only ∼15 per cent in both stands and seed orchards indicated small variations in fertility. Fertility variation was higher in stands than in seed orchards. Differences in fertility were usually higher during poor flowering years and in young populations. In seed orchards, fertility differences were slightly larger on the male side than on the female side. For fertility predictions concerning objects that are neither juvenile nor characterized by poor flowering, we suggest, for seed orchards, a CV equal to 100 per cent with Ψ equal to 2 and, for stands, a CV equal to 140 per cent with Ψ equal to 3.