Colonization Pattern of Abandoned Croplands by Quercus pyrenaica in a Mediterranean Mountain Region

Land abandonment is a major global change driver in the Mediterranean region, where anthropic activity has played an important role in shaping landscape configuration. Understanding the woodland expansion towards abandoned croplands is critical to develop effective management strategies. In this study, we analyze the colonization pattern of abandoned croplands by Quercus pyrenaica in the Sierra Nevada mountain range (southern Spain). We aimed to assess differences among populations within the rear edge of the Q. pyrenaica distribution. For this purpose, we characterized (i) the colonization pattern of Q. pyrenaica, (ii) the structure of the seed source (surrounding forests), and (iii) the abundance of the main seed disperser (Eurasian jay, Garrulus glandarius). The study was conducted in five abandoned croplands located in two representative populations of Q. pyrenaica located on contrasting slopes. Vegetation plots within three habitat types (mature forest, edge-forest and abandoned cropland) were established to compute the abundance of oak juveniles. The abundance of European jay was determined using data of bird censuses (covering 7 years). Our results indicate that a natural recolonization of abandoned croplands by Q. pyrenaica is occurring in the rear edge of the distribution of this oak species. Oak juvenile abundance varied between study sites. Neither the surrounding-forest structure nor the abundance of jays varied significantly between study sites. The differences in the recolonization patterns seem to be related to differences in the previous- and post-abandonment management.

Genetic Diversity and Differentiation of Pedunculate Oak (Quercus robur L.) Populations at the Southern Margin of Its Distribution Range—Implications for Conservation

Understanding intraspecific genetic variation is one of the principal requirements for the evaluation of tree species capacity to cope with intensive climatic changes, as well as designing long-term conservation programs. Herein, we evaluated the genetic diversity and genetic structure of seven pedunculate oak (Quercus robur L.) populations, located at the southern margin of its distribution range on the Balkan Peninsula (Serbia). The objective of the study was to propose future in situ conservation measures aimed at protection of pedunculate oak adaptive and neutral genetic diversity at the species rear-edge. Genetic diversity and structure were estimated using twelve highly polymorphic simple sequence repeat (SSR) markers. The mean expected heterozygosity (He) was 0.769, allelic richness (AR) 9.63, and private allelic richness (pAR) 0.79, indicating high genetic diversity in the studied populations. Genetic differentiation among the populations was low (Fst = 0.032). Structure analysis, the unweighted pair group method with arithmetic mean (UPGMA) showed the existence of two gene pools unrelated to the populations’ area of occurrence. Taking into consideration the results of the current study and previous conservation activities on the pedunculate oak in Serbia, as well as the importance of rear-edge populations in the long-term conservation of the species genetic diversity, we suggested establishing three additional gene conservation units for securing long-term sustainability of the species.

Interspecific gene flow and vicariance in Northern African rear-edge white oak populations revealed by joint analysis of microsatellites and flanking sequences.

Rear-edge populations represent reservoirs of potentially unique genetic diversity but are particularly vulnerable to global changes. While continental-scale phylogeographic studies usually do not cover these populations, more focused local scale study of rear-edge populations should help better understand both past evolutionary history and its consequences for the persistence and conservation of these potentially unique populations. We studied molecular variation at 36 sequenced nuclear microsatellites in 11 rear-edge Quercus faginea and Q. canariensis populations across Algeria to shed light on taxonomic relationship, population past evolutionary history and recent demographic trajectory. We used descriptive approach and simulation-based inference to assess the information content and complementarity of linked microsatellite and flanking sequence variations. Genetic differentiation among populations classified into eight well-defined genetic clusters do not allow to unambiguously delineate two species. Instead, continuous level of genetic differentiation indicates interspecific gene flow or drift in isolation. Whereas the analysis of microsatellite variation allowed inferring recent interspecific gene flow, additional nucleotide variation in flanking sequences, by reducing homoplasy, pointed towards ancient interspecific gene flow followed by drift in isolation. The assessment of the weight of each polymorphism in the inference demonstrates the value of linked variation with contrasted mutational mechanisms and rates to refine historical demographic inference. Past population size decline inferred in some of these oak populations as well as low contemporary effective population size for most populations is a concern for the persistence of these populations of high evolutionary significance and conservation value.