This is a special seminar connecting to the impact of Gösta Eriksson and Inger Ekberg on forest genetics, and thus an appropriate time to connect the past and the future. I will show data from a quarter of a century ago, when we worked as a group, and how this links to the future, thus a PhD-thesis, which will be presented next week. It is about differences in fertility. Observations from a Norway spruce seed orchard and Norway spruce stands in southern Sweden were made on initiative by Gösta Eriksson and are reported for the first time in English (earlier "published" in Swedish, e.g. by Lindgren et al 1976) as follows:

Year N_e/N flowering

1968 0.57 intermediate

1972 0.16 very poor

1973 0.17 very poor

1974 0.68 rich

1975 0.56 rich

Inventories of cones in 31 Norway spruce stands were done in Southern Sweden during three years (1973-75). N_e/N=1/A, thus effective population size versus real effective population size, related to cone crop as follows

Cone crop N_e/N

Rich 0.60

Intermediate 0.35

Poor 0.15

These and similar observations inspired me to continue according to these lines.

Many other observations have been done, although for "forests" the observations referred to above still are an important part of all data (Bila 2000). It seems like years and objects (stands, seed orchards) characterised by poor flowering also harbour larger variations in fertility. Differences over time and differences between sexes ("sexual asymmetry") tend to make overall differences less drastic, thus the "effective" fertility variation is probably below average of what is observed in individual objects.

These observations concern gamete production ability, which is close to reproductive success. The link between generations is the successful gametes. The gene pool of the successful gametes from the parental generation is the same as the gene pool of the offspring. Thus the effective number (status number) of the successful gametes is the same as the effective number of the offspring.

Estimates are needed for planning. Some rough and a bit "conservative" generalisations are suggested for this purpose. A seed orchard crop typically has an effective number (status number), which is half of what it should have if all clones were equally fertile. Seed crops from conifer tree stands (plantations) typically have an effective number, which is one third of what they should have if all trees were equally fertile.

Bila AD 2000. Fertility variation and its effects on gene diversity in forest tree populations. Silvestria 166. Ph D thesis.

Lindgren, D. and Lindgren, K. 1976. The effective population size of Norway spruce. In: Proceedings from Conference on Forest Genetic Resources. The Department of Forest Genetics, The Swedish College of Forestry, Stockholm. p 125-135.