Time trends in genetic control over height and diameter in maritime pine

Height and diameter of 257 twenty-year-old maritime pine (Pinus pinaster Ait.) trees, originating from a factorial mating design, were subdivided in annual height increments (AHI) and annual diameter increments (ADI). Cumulative and annual data of both traits were compared using two different genetic models. The two traits exhibited very different genetic expressions. For cumulative data, the heritability increased steadily with age for height and was very stable for diameter. For annual data, this evolution did not reveal any particular trend for AHI but appeared much more stable for ADI. Different effects seemed to be involved in the variation of annual increments: year and residual effects were 5 and 2.5 times more important for AHI than for ADI, respectively; in contrast, family and individual effects were 10 and 15 times more important for ADI than for AHI, respectively. Serial correlations calculated at the full-sib family mean level also showed different patterns: low values and rapid decrease of correlations for successive AHI, and high values and a linear decrease for successive ADI. As trees aged, the genetic expression of height growth appeared to be more unstable than for diameter growth. Interpretations about these expressions and their consequences for early selection are discussed.