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Seed production is known to reveal high individual variation in tree populations, shaping regeneration and competition patterns. In isolated populations, individual variation in seed production drives genetic drift and inbreeding, increasing the risk of local extinction. In this study, we investigated the variation in seed production within a natural remnant population of a dioecious conifer, Taxus baccata. The observed individual seed counts were highly variable and showed excessive zeros. The observed zeros were well explained by the small trunk circumference and the absence of neighboring males. Non-zero seed counts increased with female trunk circumference, neighboring male circumference, and female heterozygosity. In addition, seed production decreased with elevation, presumably reflecting water availability at the site. We did not observe an effect of canopy closure but, since trunk circumference showed a strong relationship with canopy closure, light availability may indirectly influence seed production by determining resources available for reproduction. Overall, the study shows that seed production in yew is strongly pollen-limited. However, for similarly sized and pollen-supplemented trees, seed production may be further determined by an individual genotype and micro-environmental factors. Whether the observed variation in seed production drives density-dependent effects (e.g. mortality) in recruited seedlings remains a matter for future studies. [ABSTRACT FROM AUTHOR]

Quercus pubescens on its only stand in Poland, in the Bielinek Reserve, was for years treated as atypical, being an effect of hybridizing with co-occurring Q. petraea and Q. robur. In the study, the leaves of these three species and their hybrids in Bielinek were characterized with 20 macro-morphological and eight micro-morphological traits, and statistically compared with Q. pubescens from Italy. Genetic assignments revealed a low number of hybrids. Quercus pubescens leaves from Bielinek and Italy were visually similar, the significant differences between them concerned mainly the size of the leaves. It was accepted that the characteristics of Q. pubescens from Bielinek were within the range of species variability and were similar to the doubtful species Q. virgiliana (Q. pubescens s.l.). Differences between Q. pubescens from Bielinek and Italy could have resulted from the acclimatization to the local conditions, or origination form a different refugium, and long-term isolation. The group of Q. petraea leaves joining morphological features of Q. petraea and Q. pubescens was detected, blurring the morphological differences between species and impeding the recognition of hybrids. This phenomenon is explained by the acclimatization of part of the population to the local micro-climate or by the ancient hybridization. [ABSTRACT FROM AUTHOR]