Analysis of inbreeding depression in managed versus natural Scots pine populations

Goal The plan has been to study the impact of two different forest regeneration practices (plantation and seed tree regeneration) on the genetic composition, spatial structure and inbreeding in Scots pine populations.

Brief discussion and conclusion The main conclusion of the results is that none of the regeneration practices (plantation and seed tree regeneration) have altered the genetic composition and its spatial distribution and the level of inbreeding. Supporting most of the previously reported studies in forest trees where the effects of multiple silvicultural and breeding practices were investigated.

In seed tree regeneration stands, a relatively low number of large trees are left to reproduce, however, the effect of this practice on the level of genetic diversity and inbreeding is often undetected (Neale, 1985; Yazdani et al 1985; Cheliak et al 1988). The absence of detectable genetic changes may be as a consequence of the slow decrease in genetic variability with drift, at the rate of 1/2e per generation (where e is the effective population size). Similarly, seed orchards and forests regenerated with seedlings of seed orchard origin will lose very little of the expected heterozygosity in one generation even if they contain a moderate number of genotypes. Empirical studies support this hypothesis where genetic variability (Shaw and Allard, 1982; Muona and Harju, 1989; Icgen et al 2007) and inbreeding (Muona and Harju, 1989; Barret et al 1987; Moran et al 1989) are reported to maintain at similar levels in the seed orchards compared to the natural populations. However, some of the important genetic variability may be in the form of rare alleles, which are typically lost in seed orchards (Hattemer et al 1982; REFs). Marquardt et al (2007) observed higher spatial genetic structure and inbreeding in an undisturbed old population compared to a plantation regenerated from bulked seed, while the level of genetic diversity (heterozygosity) was similar in both sites.

Therefore, based on the preliminary observation and interpretation of our results we can conclude that the silvicultural practises applied in the Swedish forests preserve the level and structure genetic make up, and do not increase the level of inbreeding. However, sibship reconstruction revealed a somewhat un expected scenario indicating that all sites are composed of a substantial number of half- and full-sib families. This result is however difficult to contrast with previous studies on the topic because report on sibship reconstruction on those type of studies is rare. This result warrants further investigation.

Note: these conclusions are based on a still on going investigation of the data, therefore, possible changes in the conclusions cannot be ruled out. We highlight that the present conclusions need to be taken with caution until the manuscript is fully finished.