Published in "Australian Forestry 81(4): 239–249, 2018" which should be cited to refer to this work. The ongoing naturalisation of Eucalyptus spp. in the Mediterranean Basin: new threats to native species and habitats E. Badalamentia, D. Cusimanoa, T. La Mantia a, S. Pastab, S. Romanoc, A. Troia d and V. Ilardic aDepartment of Agricultural, Food and Forest Sciences, University of Palermo, Palermo, Italy; bDepartment of Biology, Unit of Ecology and Evolution, University of Fribourg, Chemin du Musée, Fribourg, Switzerland; cDepartment of Earth and Marine Sciences, University of Palermo, Palermo, Italy; dDepartment of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), Section of Botany and Plant Ecology, University of Palermo, Palermo, Italy ABSTRACT The genus Eucalyptus has been widely introduced into many regions of the world outside its native range and has become invasive in some Mediterranean biomes (e.g. in southern Africa and California). In the Mediterranean Basin and Europe, eucalypts were introduced at the end of the KEYWORDS 18th century. However, natural regeneration events in these regions are recent in time and limited biological invasions; insular in terms of affected areas, except for the Iberian Peninsula. An updated overview about the natural ecosystems; river red gum; spread of Eucalyptus species in Italy is still lacking. This paper aims to fill this knowledge gap, using Eucalyptus camaldulensis; both published data and unpublished field data regarding naturalisation events, with a specific Eucalyptus globulus; focus on Sicily. Three species have naturalised on the island: Eucalyptus camaldulensis, E. globulus Eucalyptus occidentalis; Alnus and E. occidentalis. According to our data, E. camaldulensis showed a clear ‘switch’ in the past glutinosa decade towards naturalisation and invasive behaviour on the pebbly shores of watercourses that have a torrential rainfall regime and erodible substrates, threatening native plant communities and species. Alluvial forests with Alnus glutinosa were found to be particularly vulnerable to E. camaldu- lensis invasion. This is significant because the A. glutinosa communities are a native habitat of particular conservation value and protected under the Habitats Directive 92/43. The uncontrolled spread of Eucalyptus species may represent a higher threat to native biodiversity than previously considered. The situation in Sicily could be indicative of the invasion process by eucalypts currently ongoing around the Mediterranean Basin, the management of which requires special attention, urgent action and sound choices. Introduction underrepresented in invasive alien flora databases world- wide (Richardson & Rejmánek 2011). This is in contrast to The genus Eucalyptus (Family Myrtaceae; L’Héritier de other widely introduced tree species such as Acacia spp. and Brutelle 1788), consisting of more than 700 species Pinus spp., both including a large number of well-known (Paczkowska & Chapman 2000; Slee et al. 2006), mostly invasive taxa (e.g. Pasta et al. 2012; Badalamenti et al. trees native to Australia, has been widely introduced outside 2014). This circumstance led Forsyth et al. (2004, p. 76) to its native range, particularly during the last two centuries. state about eucalypts: ‘They have, however, been markedly The success of such introductions has to be attributed to the less successful as invaders than several other tree genera (for peculiar biological traits of eucalypts, such as rapid growth example, pine trees in the genus Pinus) that have enjoyed rate, ecological plasticity and pioneer features. The introduc- similar levels of dissemination as aliens’. tions have also been encouraged by the many utilities that Eucalypts mainly invaded the Mediterranean biomes of http://doc.rero.ch eucalypts are able to provide, including forest products the world, but in the Mediterranean Basin natural reproduc- (cellulose, firewood, poles, essential oils, pulpwood), envir- tion events are recent in time and limited in terms of onmental applications (dune stabilisation, windbreaks, recla- affected areas, except for the Iberian Peninsula (Andreu mation of marshlands), and ornamental and aesthetic values et al. 2009; Fernandes et al. 2016). The two most widespread (Forsyth et al. 2004; Ritter & Yost 2009; La Mantia 2013). The species in the world are Eucalyptus globulus Labill. and high growth rates of eucalypts place them among the Eucalyptus camaldulensis Dehnh., which have a different nat- woody species most frequently used worldwide for silvicul- ural distribution range, reflecting auto-ecological differences ture (Florence 1996), as well as for arboriculture and short (Burges 1968; Paczkowska & Chapman 2000). Eucalyptus glo- rotation coppices. For these reasons, extensive plantations bulus has become naturalised in several areas with oceanic have been established in the Mediterranean Basin, particu- and sub-tropical climate, but also in Mediterranean countries larly on the Iberian Peninsula, but also in southern Africa, such as Spain (Sanz-Elorza et al. 2001), Rhodes island in California, China and Brazil. Greece (Galanos 2015) and Sicily (Italy) (Giardina et al. Although the Eucalyptus genus is valued for its utilitarian 2007). Eucalyptus camaldulensis showed a marked preference traits, it is also represented in the Global Compendium of for Mediterranean-climate areas, including California, South Weeds (Randall 2012), where more than 100 eucalypt spe- Africa and the Mediterranean Basin (Ritter & Yost 2009; cies are listed. However, so far this genus is currently Tererai et al. 2013), where it naturalised in Spain (Sanz- CONTACT T. La Mantia [email protected] Department of Agricultural, Food and Forest Sciences, University of Palermo, Viale delle Scienze Ed. 4, I-90128 Palermo, Italy 1 Elorza et al. 2001), Portugal (Almeida & Freitas 2006), Greece information collected has been used to identify the potential (Arianoutsou et al. 2010), North Africa (Vilà et al. 1999) and risks posed by eucalypt invasion to the conservation of Italy (Celesti-Grapow et al. 2010). native biodiversity and ecosystem functioning and develop Some consistent patterns have been found in eucalypt alert levels and management options. We conclude that as invasion worldwide. In many areas their current invasive eucalypts occur naturally in areas with a Mediterranean status is still under debate, and subject to discussions and climate, they may represent a higher threat than previously revision. In South Africa, seven Eucalyptus species had been thought or recorded in invasive checklists. listed in the Conservation of Agricultural Resources Act 1983 (Act No. 43), and were subject to stringent limitations for the cultivation and trade to prevent their further spread. Materials and methods However, a recent paper showed that only E. camaldulensis, Eucalyptus grandis W.Hill and Eucalyptus lehmannii (Schauer) The widely accepted classification of alien species by Pyšek Benth. have been considered invasive (Forsyth et al. 2004). et al. (2004) was used in this study. Casual alien plants are Eucalyptus camaldulensis is also regarded as transformer defined as those that give rise only to ephemeral and occa- species (sensu Pyšek et al. 2004), due to its ability to deeply sional phenomena of natural regeneration, relying on change the structure and functioning of riparian habitats, as repeated introductions for their persistence. Naturalised well as seriously threatening native biodiversity. plants may form self-replacing populations for at least In California, 374 Eucalyptus species have been intro- 10 years without direct human intervention but only inva- duced since 1853 (Ritter & Yost 2009). Among them, how- sive taxa are able to actively spread into new habitats, and at ever, only 18 species have found suitable conditions for considerable distances from the mother plants. To identify natural regeneration and survival outside cultivation, becom- Eucalyptus taxa as casual, naturalised or invasive in ing naturalised; the two most common species are E. camal- Mediterranean Europe, the information available in the dulensis and E. globulus. Both species are considered harmful most recent non-native flora databases, at European aliens for the conservation of semi-natural and natural habi- (DAISIE 2009), national (Viegi et al. 1974; Celesti-Grapow tats in Spain (Sanz-Elorza et al. 2001). In Spain, the cost et al. 2010) and regional level (Raimondo et al. 2004), was incurred for the control of eucalypts between 2000 and primarily considered. Other specific contributions concern- 2009 amounted to €30 million, about 60% of the total ing the regional non-native floras, including Eucalyptus spe- costs incurred for all the invasive alien plants (Andreu et al. cies (e.g. Camarda et al. 2016), were also taken into account. 2009). In Malta, the propagation, sowing and planting, For Sicily, the most updated regional checklists were con- import/export, transport and sale of E. camaldulensis and sidered (Giardina et al. 2007; Raimondo et al. 2010), along Eucalyptus gomphocephala A. Cunn. ex DC. are prohibited, with other publications about non-native or ornamental due to their negative ecological impacts (MEPA 2013). flora reporting eucalypts (e.g. Domina & Mazzola 2008). Portugal deserves a particular mention, probably being Eucalypt natural regeneration has rarely been explicitly home of the first known naturalisation event of eucalypts cited in the main literature, either at national or regional