Mechanisms involved in alien maples (Acer sp.) invasion process in the Central Europe. Testing hypotheses associated with species fitness

Abstract

Maples (Acer sp.) are trees/shrubs of extraordinary aesthetic value, what favours them for wide utilisation in urban greenery. However, some of the non-native species became invasive in the new range and represent a threat to natural ecosystems. Therefore, after the definition of their frequency and planting history in Slovak cities and reinvestigation of ecological status, based on analysis of growth, reproduction biology, fruit dispersal, phenotypic plasticity and allelopathic potential, invasion hypotheses related to the species fitness were tested in non-invasive alien species, in respect of invasive box elder (A. negundo L.). Parks and residential areas from the socialistic era were dominated by silver maple (A. saccharinum L.) and private gardens by palm maple (A. palmatum Thunb.) cultivars. A shift to ´locally naturalised´ was confirmed in the former, and palm maple was taken into consideration in the alien flora list (as casual). The fastest growth was found in silver maple and box elder. The latter showed also extraordinary reproduction earliness, largest fruit production, flight range and seed viability. Specific leaf area mostly decreased in box elder towards summer, indicating its large phenotypic plasticity. However, the largest allelopathic effect was observed in silver maple. Hence, ´limiting similarity hypothesis´, ´ideal weed hypothesis´, ´propagule pressure hypothesis´ and ´phenotypic plasticity hypothesis´ were essential for box elder invasion success. On the other hand, ´ideal weed hypothesis´ and ´novel weapon hypothesis´ seem to be crucial for silver maple naturalisation. Palm maple failed in all studied aspects, indicating colonisation stage of the invasion process.