Annual Variability in Cone and Seed Yields Across Seed Stands of Taurus Cedar (Cedrus libani) and Its Impact on Gene Diversity of Seed Crops

The variation in annual cone and seed production was examined for three natural seed stands of Taurus cedar (Cedrus libani A. Rich., Pinaceae), each with distinct structural characteristics, sampled from 35 trees for three consecutive years. Fertility variation (Ψ), estimated by cone (ΨC) and seed (ΨS) yields per tree, was also analyzed to contribute to the management and development of silvicultural practices for the seed stands of the species. Significant differences (p < 0.05) were recorded in cone and seed production across years, between populations, and between trees within a population. Population x year interactions were also significant (p < 0.05), highlighting the importance of seed harvesting year in cone collection. Fertility variation in cones and filled seeds showed only small deviation [ΨC = 1.10 (91% of census number)–1.71 (59%), Ψs = 1.25 (80%)–1.71 (59%)] among the seed stands in different years, except ΨS = 2.38 (42%) in a population in one year. The cone and seed fertility were at acceptable levels for an ideal natural population (Ψ ≤ 3). Figures of parental balance curves showed that the contribution to the gamete gene pool was much closer to equal for cone production across the years than for filled seed production in both individual stands and pooled stands, suggesting that the number of cones is a good indicator of overall seed production. Difference in gene diversity (GD) was 0.005 from individual year (GD = 0.992 and 0.993) to pooled years of the populations (GD = 0.997 and 0.998) for both cone and seed yields, while it was higher among years within population (e.g., 0.017 for cone yield and 0.026 for seed yield in a population).