Analysis of chosen growth and reproductive traits of manna ash (Fraxinus ornus) with regards to its expansive properties

Abstract

Manna ash (Fraxinus ornus L.) is a Mediterranean shrub or a small tree with the northern limit of its natural range in central Europe. At the same time, it is also a tree species which, due to its considerable tolerance to high temperatures and lack of moisture, as well as some expansive properties, could be expected to increase its range in the coming decades as a result of the changing climate and the associated spontaneous spread. The paper summarizes the results of several years of our research, during which we evaluated the following growth and reproductive characteristics: (1) phenological traits and the length of the growing season, (2) the intensity and evenness of fruiting, and (3) the numbers of individuals and stems according to the height categories. In addition, the species composition of vegetation cover was analysed on the sites with the occurrence of manna ash. Observations were made in two autochthonous populations of manna ash in Southern Slovakia and one allochthonous population in its central region. The onset of spring vegetative and generative phenophases showed a noticeable latitudinal trend during our observations (2015‒2019). In Central Slovakia, flowering and leafing of manna ash occurred on average more than two weeks later than in its southernmost region. The “Central Slovakian” population of manna ash was also characterised by the earliest onset of autumn vegetative phenophases and the lowest total length of the growing season. Despite these trends, flowering and fruiting in this population were relatively regular ‒ in contrast to the other two sites, it was observed every year. In this locality, we also observed the highest total numbers of individuals and stems in all the height categories and the markedly decreased occurrence of competing species. The achieved results point out to the considerable vigour and high reproductive ability of the allochthonous population of manna ash outside its natural range and the natural range of its most important competitors.