Effects of tree size and park maintenance on soil seed bank of Gleditsia triacanthos, an exotic tree in urban green areas

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 cm 3 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/m 2 and in 17 out of 48 cases, it exceeded 100 seeds/m 2. 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 fivetimes higher density on average than those in perfectly managed parks (126.4 and 24.5 seeds/m 2 , 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.

Collection of Experiences: 25 Years’ Work on Seed Propagation of Allochthonous Woody Plants in Skopje and Their Possible Role in the Urban Landscape

“…In urban and suburban areas, vegetation provides a myriad of services, i.e., microclimate regulation, moisture increase, air cooling, oxygen supply, noise reduction, improvement of the radiation regime, suspended particulate matter filtration, wind reduction or redirection, supporting the diversity of arthropod and vertebrate communities, etc. (Attorre et al 2000, Schmitt-Harsh et al 2013, Irmak et al 2018, Frank et al 2019, Rita Baraldi et al 2019, Csontos et al 2020, Ribeiro et al 2020, Masalova et al 2021. Furthermore, trees also have a mnemonic and social role, and green infrastructure has the potential to give new life to the city after a catastrophic event, build solidarity and commemorate the past (Magnus and Sander 2019).…”

“…While active invasion is a result of the introduction of species that spread quickly and easily under suitable new conditions, passive invasive mechanisms refer to species that have been present for a long time and/or are present in considerable numbers, and thus become more dominant (Trusty et al 2007). Regardless of the mechanism, the risks of these allochthonous species is a potential escape from the borders of their cultivation in (semi) natural areas and the establishment of self-sustaining stands where they might exhibit invasive behaviour (Csontos et al 2020). Which species exhibit invasive behaviour depends not only on their biological characteristics, but also on the environmental conditions.…”

“…Considering that these species have been characterized either as 'common' or 'abundant', and with medium or high germination rate (Table 1), they impose a need for close monitoring in urban green areas. As the literature notes, Gleditsia triacanthos and Koelreuteria paniculata have been characterized as being able to establish high-density soil seed banks underneath the canopy with viable, hard-coated seeds which can be further dispersed by birds and mammals to great distances (Csontos et al 2020, Ljubojević et al 2021. Paulownia tomentosa Thunb.…”

“…The impact of invasive allochthonous species on recreational ecosystem services that are urbanized on various levels is an emerging field of interest as these species also affect the use of the recreational areas, thus influencing how people see them and how they value them (Sikorska et al 2019). Prevention by regular and planned management, raising awareness and biological investigations of the seeds are crucial steps to reduce the potential risk of increased presence of invasive species in both urban and suburban environments (Csontos et al 2020, Deparis et al 2022. Alternative scenarios for using invasive species have also been considered, e.g., using various parts of Amorpha fruticosa as a resource for remedial purposes (Kozuharova et al 2017) and Koelreuteria paniculata seeds as a novel feedstock for biodiesel production (Ljubojević et al 2021).…”