Local and regional assessments of the impacts of plant invaders on vegetation structure and soil properties of Mediterranean islands

Abstract

Aims Although biological invasions occur throughout the world, and some invaders are widespread in many habitats, few studies on the ecological impact of invaders have examined multiple sites. We tested how the impact of three widespread plant invaders changed depending on the identity of the species and the invaded island. We also tested whether relative species loss was lower in species-rich communities than in species-poor ones.Location We conducted floristic surveys and soil analyses in eight Mediterranean Basin islands: Crete and Lesbos (Greece), Sardinia (Italy), Corsica, Bagaud and Porquerolles (France), and Mallorca and Menorca (Spain).Methods We compared native species richness and diversity, proportion of life forms, soil percentage nitrogen, percentage organic carbon, C/N, and soil pH in nearby paired plots of 2 · 2 m: one control and one invaded by either the deciduous tree Ailanthus altissima, the succulent subshrubs Carpobrotus spp. or the annual geophyte Oxalis pes-caprae, across eight Mediterranean Basin islands.Results On average, the presence of invaders reduced species diversity, Carpobrotus spp. exhibiting the largest impact and Oxalis the least. However, the relative impact was island-dependent, and was positively but weakly associated with the species richness of the recipient community. Therophytes were the life form that experienced the largest decrease across islands. The effects of invasion on soil properties were very variable. Total N changed (increased) only in plots invaded by Ailanthus, significantly decreasing the C/N ratio. The presence of this tree increased soil pH, whereas the opposite was found in plots invaded by the other two species. Organic C increased in plots invaded by Ailanthus and Carpobrotus species.Main conclusions By conducting an analysis at multiple sites, we found that the three plant invaders had an impact on plant community structure not entirely concordant with changes in soil properties. The impacts depended on the identity of the species and of the invaded island, suggesting that impact of invaders is context-specific. The impact in terms of species loss was not lower in species-rich than in species-poor communities.

Seasonal effects on mortality rates and resprouting of stems treated with glyphosate in the invasive tree of heaven (Ailanthus altissima(Mill.) Swingle)

“…One of the most prominent tree invaders worldwide is A. altissima (also known as Tree-of-Heaven, hereafter Ailanthus), a fast-growing deciduous tree that is particularly aggressive and widespread in temperate and Mediterranean-climate areas (Badalamenti, Barone, Pasta, Sala, & La Mantia, 2012;Meloche & Murphy, 2006;Vilà et al, 2006). The broad use, mainly for ornamental or afforestation purposes, and peculiar eco-physiological and reproductive traits allowed the naturalisation and spread of Ailanthus from its native range -China and north Vietnam -to Europe, USA and many other regions around the world (Kowarik & Säumel, 2007).…”

Comparación de la flora exótica vascular en sistemas de islas continentales: Cerdeña (Italia) y Baleares (España)

“…ej., Lloret & al., 2004;Vilà & al., , 2006Hulme & al., 2008b; Bacchetta & al., 2010); sin embargo, son esca-L. Podda & al. sas las contribuciones que consideran el conjunto de la flora exótica de un territorio, comparándola con la flora autóctona y con las floras, tanto exóticas como autóctonas, de áreas pertenecientes a la misma región biogeográfica mediterránea.…”

Distribution pattern of the invasive alien plant Bunias orientalis in Rów Podtatrzański trench, north of the Tatra Mts, Poland

“…Invasions by alien plants often results in reduced biodiversity (e.g., Pyšek & Pyšek 1995;Vilà et al 2006;Hejda et al 2009;Foggi et al 2011). Brandes (1991) found that stands dominated by B. orientalis contained a smaller number of species than those with low abundance of B. orientalis.…”

“…Biological invasions are regarded to be amongst the most important drivers of adverse changes to ecosystems (Parker et al 1999;Mack et al 2000;Vilà et al 2006). Alien invasive species may inflict significant and costly damage to both natural and managed ecosystems (Manchester & Bullock 2000), requiring very expensive control measures (Pimentel 2011).…”