Abstract
The exotic honey locust (Gleditsia triacanthos) is often planted as ornamental tree in urban parks. In Hungary, it occasionally escapes cultivation, in other countries it has already become invasive, and thus, further spread cannot be ruled out. The production of copious long-lived seeds may contribute to its invasiveness. We investigated the soil seed bank of honey locust growing in urban parks of Budapest (Hungary). Soil samples of 1200 cm3 were taken under the canopy of 48 solitary female trees, seeds were extracted by washing, and their viability was assessed by germination test following scarification. For each tree, trunk circumference and level of park maintenance were recorded. Seed bank density varied between 0 and 500 seeds/m2 and in 17 out of 48 cases, it exceeded 100 seeds/m2. Larger trees tended to form better-developed soil seed bank than smaller ones, yet the level of park maintenance has a much stronger effect: trees in neglected parks produced five-times higher density on average than those in perfectly managed parks (126.4 and 24.5 seeds/m2, respectively). For a better understanding of the species’ invasion risk, detailed seed ecological studies are needed and to prevent its further spreading, a more careful treatment of its litter is recommended.
Highlights
Urban green areas in modern cities provide a number of ecosystem services for inhabitants such as noise reduction, water and air purification and microclimate stabilization (Bolund and Hunhammar 1999; Chiesura 2004; Bowler et al 2010)
In perfectly maintained parks, increasing tree size was associated with slightly higher soil seed bank densities: 23.8 seeds/m2 were encountered for big trees, while only 8.3 seeds/m2 for medium-sized ones
Examples for successful control of widely established invasive species are rare, their eradication campaign may work if there is sufficient dedication and persistence, as it has already happened with honey locust in Australia (Csurhes 2004)
Summary
Urban green areas in modern cities provide a number of ecosystem services for inhabitants such as noise reduction, water and air purification and microclimate stabilization (Bolund and Hunhammar 1999; Chiesura 2004; Bowler et al 2010). There are many non-native plant species which originally has been introduced intentionally for ornamental purposes, later escaped from cultivation, established their self-sustaining stands and became invasive, threatening native biodiversity in resident (semi)natural ecosystems in the countryside (Essl 2007; Čeplová et al 2017). Invasive plants are among the prominent conservation threats and have affected biodiversity seriously throughout the world already (Richardson and Pyšek 2006; Chmura 2013; Early et al 2016)
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