Abstract
Cities, due to the presence of ports and airports and the high diversity of trees in streets, parks, and gardens, may play an important role for the introduction of invasive forest pests. We hypothesize that areas of urban forest facilitate the establishment of non-native forest pests. Based on scientific literature and a pan-European database on non-native species feeding on woody plants, we analysed where the first detections occurred in European countries. We collected site data for 137 first detections in Europe and 508 first European country-specific records. We also estimated the percentage of tree cover and suitable habitat (green areas with trees) in buffers around detection points. The large majority of first records (89% for first record in Europe and 88% for first records in a European country) were found in cities or suburban areas. Only 7% of the cases were in forests far from cities. The probability of occurrence decreased sharply with distance from the city. The probability to be detected in urban areas was higher for sap feeders, gall makers, and seed or fruit feeders (>90%) than for bark and wood borers (81%). Detection sites in cities were highly diverse, including public parks, street trees, university campus, arboreta, zoos, and botanical gardens. The average proportion of suitable habitat was less than 10% in urban areas where the species were detected. Further, more than 72% of the cases occurred in sites with less than 20% of tree cover. Hotspots of first detection were identified along the coastal regions of the Mediterranean and Atlantic, and near industrial areas of central Europe. We conclude that urban trees are main facilitators for the establishment of non-native forest pests, and that cities should thus be intensely surveyed. Moreover, as urban areas are highly populated, the involvement of citizens is highly recommended.
Highlights
Forests, like other terrestrial ecosystems, are increasingly threatened by the establishment and spread of non-native pests worldwide (Brockerhoff and Liebhold 2017)
Some examples of forest invasive species with large distribution range are the Pine wood nematode, Bursaphelenchus xylophilus, causing the pine wilt disease in Asia (Kishi 1995; Robinet et al 2009) and Europe (Sousa et al 2001); the Emerald ash borer, Agrilus planipennis, in North America (Herms and McCullough 2014); Anoplophora glabripennis which was introduced into North America and Europe (Carter et al 2010; Roques et al 2010); the invasion of the USA by the gypsy moth, Lymantria dispar (Liebhold et al 1992); or the increasing numbers of Eucalyptus pests established in all continents where eucalypts are grown in intensive plantations (Hurley et al 2016)
We conclude that surveillance and monitoring for invasive forests pests should be focused on trees in urban and suburban areas
Summary
Like other terrestrial ecosystems, are increasingly threatened by the establishment and spread of non-native pests worldwide (Brockerhoff and Liebhold 2017). The increase of forest pest invasions in recent years is mostly the consequence of increasing global trade and international travel (Brockerhoff et al 2006a; Roques 2010). The main pathways for the accidental introduction of non-native forest insects are the trade of live trees for planting, hitchhiking with containers, imports of timber, and use of wood packaging material (Brockerhoff and Liebhold 2017), all of which are much more frequent than in the past. In particular large cities, are close to international airports and seaports and are expected to be main gateways for the entry of new, non-native insect species. In Europe, where urbanization occurred earlier, 82% of people are already living in cities (United Nations 2018)
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