Figure 3.

Relative contributions (that is, as a proportion of the phenotypic variance) to the total heritable variance due to the variances associated with direct and indirect genetic effects, and to their covariance, for breast-height stem diameter (DBH) growth at ages 2, 4 and 8 years, and for a damage due to a transient outbreak of Mycosphearella leaf disease (MLD) occurring at age 2 years, estimated using the full (FS) and reduced (RS) sets of neighbor positions. There is a marked contrast of the impact of IGEs on disease damage compared with growth: for MLD, the positive direct–indirect covariance (indicative of infection) significantly increased the total heritable variance in the population compared with the direct genetic variance; conversely, for DBH, the negative direct–indirect covariance (indicative of competition) resulted in a substantial decrease of the total heritable variance. For DBH, the relative magnitude of the indirect genetic variance and the direct–indirect genetic covariance increased more with age than the direct genetic variance did, but less between ages 4 and 8 years than between ages 2 and 4 years, leading to a stabilization of the impact of competitive interactions on the heritable variance at the later age. Further details on these results are provided in Supplementary Table S4 (Supplementary Information).