Plant invasion as an emerging challenge for the conservation of heritage sites: the spread of ornamental trees on ancien
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ORIGINAL PAPER
Plant invasion as an emerging challenge for the conservation of heritage sites: the spread of ornamental trees on ancient monuments in Rome, Italy Laura Celesti-Grapow
. Carlo Ricotta
Received: 30 June 2020 / Accepted: 23 November 2020 Ó The Author(s) 2020
Abstract Cultural heritage sites such as historical or sacred areas provide suitable habitats for plants and play an important role in nature conservation, particularly in human-modified contexts such as urban environments. However, such sites also provide opportunities for the spread of invasive species, whose impact on monuments has been raising growing concerns. The aim of this study was to investigate the patterns of distribution and spread of invasive plants in heritage areas, taking the city of Rome as an example. We focused on woody species as they pose the greatest threat to the conservation of monuments, owing to the detrimental effects of their root system. We analysed changes in the diversity and traits of native and non-native flora growing on the walls of 26 ancient sites that have been surveyed repeatedly since the 1940s. We found that the diversity of the native flora has steadily decreased, while there has been an increase in non-native, larger and more damaging species. The introduced species that have expanded most are ornamental wind- or bird-dispersed trees, which represent a major management problem as their propagules can reach the upper sections of the monuments, where they become more difficult to control. The most widespread and damaging of such species is Ailanthus altissima, which has recently been L. Celesti-Grapow (&) C. Ricotta Department of Environmental Biology, Sapienza University, Piazzale Moro, 5, 00185 Rome, Italy e-mail: [email protected]
included among the invasive species of European Union concern (EU Regulation 2019/1262). Our findings show that plant invasion is an emerging challenge for the conservation of heritage sites and needs to be prioritized for management to prevent future expansion. Keywords Ailanthus altissima Biodeterioration EU regulation on invasive alien species Impacts Ornamental horticulture Urban flora
Introduction Culturally protected sites, such as monumental or sacred sites, play an important role in nature conservation throughout the world (Bhagwat and Rutte 2006; Verschuuren et al. 2010; Gao et al. 2013; Frascaroli et al. 2016; Woods et al. 2017), particularly when they are located in environments that have been markedly modified by man, such as agricultural landscapes (Frosch and Deil 2011). In cities, they are even more crucial (Jackson and Ormsby 2017) because they become part of a network of green spaces such as parks (Nielsen et al. 2014) and road verges (Rupprecht and Byrne 2014; Sa¨umel et al. 2016) that can deliver numerous ecosystem services and play a key role in the conservation of urban biodiversity (Shwartz et al. 2014; Kowarik et al. 2016; Planchuelo et al. 2019).
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L. Celesti-Grapow, C. Ricotta
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