Protecting populations in their natural habitat allows for the maintenance of naturally evolved adaptations and ecological relationships. However, the conservation of genetic resources often requires complementary practices like gene banks, translocations or reintroductions. In order to minimize inbreeding depression and maximize the adaptive potential of future populations, populations chosen for ex situ conservation should be selected according to criteria that will result in a reduction of global coancestry in the population. Generally, large populations should reveal lower coancestry and higher genetic variation than small populations. If detailed knowledge about coancestry is lacking, census population number (N c ) can be used as a proxy for required characteristics. However, a simple measure of N c may be misleading in particular cases as genetic processes rely on effective population size (N e ) rather than N c and these two measures may differ substantially due to demographic processes. We used an example of English yew to address whether N c can be a good predictor of genetic parameters when used in conservation programs. Using microsatellite markers, we estimated allelic richness, inbreeding and coancestry coefficients of six relatively large yew populations in Poland. Each population was characterized by N e using the linkage disequilibrium method. Our results showed that populations of English yew were subject to substantial divergence and genetic drift, with both being inversely proportional to the effective subpopulation size (N e ). Additionally, allelic richness appeared proportional to N e but not to N c . However, the N e /N ratio differed greatly among populations, which was possibly due to different population histories. From the results we concluded that choosing source populations based only on their census size can be fairly misleading. Implications for conservation are briefly discussed.

Peripheral populations may be crucial for understanding processes underlying adaptive genetic variation. Their evolution and ecology are driven by various genetic and demographic processes, such as selection, gene flow and bottleneck. Peripheral populations often experience a reduction in density resulting in the Allee effect. The presence of interfertile species increases the opportunity for hybridisation, which allows for a rescue from the Allee effect, but at the risk of genetic extinction through introgression. In this article we investigated a peripheral population of Quercus pubescens, a European tree species. The study population is located in Poland, several hundred kilometres northwards from the main species range. Due to geographic separation, the study population exists under strong pressure of introgression from potentially inter-fertile Q. petraea and Q. robur, which are the only common oaks in Poland. The intermediate morphology between typical Q. pubescens and a common oak species found in the study population supports the introgression hypothesis, which could be in line with the earlier studies of this species complex conducted in the main range of Q. pubescens. Alternatively, the intermediate morphology could reflect the founder effect or selection at an ecological extreme. We attempted to verify these hypotheses using microsatellites and a reference of common oak species. The results showed that the study population is genetically distinct from both Q. petraea and Q. robur. Additionally, the population is characterised by a low effective population size and limited gene dispersal. This suggests that the study population reveals strong reproductive isolation from common species, implying alternative sources of atypical morphology.