Gene flow of common ash (Fraxinus excelsior L.) in a fragmented landscape

Abstract

Gene flow dynamics of common ash (Fraxinus excelsior L.) is affected by several human activities in Central Europe, including habitat fragmentation, agroforestry expansion, controlled and uncontrolled transfer of reproductive material, and a recently introduced emerging infectious disease, ash dieback, caused by Hymenoscyphus fraxineus. Habitat fragmentation may alter genetic connectivity and effective population size, leading to loss of genetic diversity and increased inbreeding in ash populations. Gene flow from cultivated trees in landscapes close to their native counterparts may also influence the adaptability of future generations. The devastating effects of ash dieback have already been observed in both natural and managed populations in continental Europe. However, potential long-term effects of genetic bottlenecks depend on gene flow across fragmented landscapes. For this reason, we studied the genetic connectivity of ash trees in an isolated forest patch of a fragmented landscape in Rösenbeck, Germany. We applied two approaches to parentage analysis to estimate gene flow patterns at the study site. We specifically investigated the presence of background pollination at the landscape level and the degree of genetic isolation between native and cultivated trees. Local meteorological data was utilized to understand the effect of wind on the pollen and seed dispersal patterns. Gender information of the adult trees was considered for calculating the dispersal distances. We found that the majority of the studied seeds (55–64%) and seedlings (75–98%) in the forest patch were fathered and mothered by the trees within the same patch. However, we determined a considerable amount of pollen flow (26–45%) from outside of the study site, representing background pollination at the landscape level. Limited pollen flow was observed from neighbouring cultivated trees (2%). Both pollen and seeds were dispersed in all directions in accordance with the local wind directions. Whereas there was no positive correlation between pollen dispersal distance and wind speed, the correlation between seed dispersal distance and wind speed was significant (0.71, p < 0.001), indicating that strong wind favours long-distance dispersal of ash seeds. Finally, we discussed the implications of establishing gene conservation stands and the use of enrichment planting in the face of ash dieback.

An overview of ash ( Fraxinus spp.) and the ash dieback disease in Europe.

“…The transgression zone between the central and eastern European lineage along Hungary, Slovakia, Czech Republic and Poland could be detected in a corridor of 36 km width when analysing maternally inherited cpDNA, whereas the analysis of bi-parentally inherited nuclear gene markers detected an average width of the transgression zone of 275 km [27]. Another study in Germany confirmed that, while seed dispersal is rather restricted, there is considerable pollen flow at the landscape level [53]. In former times it was believed that F. excelsior trees from floodplain forest and from dry, calcareous sites form two ecotypes, but such distinction could never be proved by reciprocal transplants or progeny trials [21,30].…”

Phenotypic diversity and plasticity index of Eurycoma apiculata populations in Eastern Sumatra, Indonesia based on leaves morphology

“…These activities greatly contributed to species rarity in the wild population, a decline of population size, habitat fragmentation, lack of natural regeneration and reduction of genetic diversity of the species (Naito et al 2005;Naito et al 2008;Leonardi et al 2012;Matesanz et al 2017;Semizer-Cuming et al 2017). E. apiculata is a rare species and difficult to find in natural habitat so that the Ministry of Environmental and Forestry has established E. apiculata as a protected species in Indonesia based on regulation No: P.20/MENLHK/SETJEN/KUM.1/6/2018.…”

Negative correlation between ash dieback susceptibility and reproductive success: good news for European ash forests

“…At the moment, we cannot predict the expected overall progress due to lack of reliable estimates of in situ heritability relevant for the two selection stages. However, the progress may be significant as strong selection seems to be involved in both stages, and effective gene flow is likely to connect surviving trees across large forest landscapes (Bacles and Ennos 2008;Bacles et al 2005Bacles et al , 2006Semizer-Cuming et al 2017). Still, it remains to be revealed whether the process will be fast and efficient enough to ensure the true recovery of the species.…”