Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Abstract

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader's effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island's general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.

Explaining variability in the production of seed and allergenic pollen by invasive Ambrosia artemisiifolia across Europe

“…Different environmental factors may act at different spatial scales (Jongejans et al 2010), and assessing the relative importance of these scales will inform whether general management strategies are applicable or if a case-by-case approach is needed (Pauchard and Shea 2006). Invader performance is therefore ideally assessed at multiple spatial scales and in various invaded habitat types within a broad distributional range, but this has only occasionally been done (Pauchard and Shea 2006;Traveset et al 2008). Performance in the field may be measured by abundance and individual performance-related demographic traits such as survival, growth and fecundity.…”

Stem-injection of herbicide for control of Ailanthus altissima (Mill.) Swingle: a practical source of power for drilling holes in stems

“…This is particularly true for some glyphosate-based herbicide, which are specifically toxic in aquatic environments. However, in terrestrial ecosystems glyphosate has low mobility, as it is rapidly adsorbed by soil colloids and eventually inactivated by microbial degradation (Schuette 1998, Busse et al 2001. For this reason, glyphosate is one of the most commonly used herbicides in natural areas (Tu et al 2001 -see also references therein).…”

<i>Acacia cyclops</i> A. Cunn. ex G. Don (Leguminosae) in Italy: first cases of naturalization

“…Among natural habitats, wetlands and coastal areas are relatively richer in IAS than other habitats, suggesting that those habitats may suffer a greater impact (Chytrý & al., 2009;Arianoutsou & al., 2010). In contrast, Mediterranean mature and stable woodlands, dominated by evergreen shrubs and trees, seem to be quite resistant to invasion (Affre & al., 2010;Arianoutsou & al., 2010;), although human disturbance, such as wildfires or silvicultural interventions, may alter canopy structure and so understory light availability, thus allowing the establishment of heliophilous tree species (Constán-Nava & al., 2010;Badalamenti & al., 2012); invasions by such species have already caused a reduction in species richness and a significant alteration of functioning of Mediterranean ecosystems (Vilà & al., 2006;Traveset & al., 2008). However, the major ecological impacts caused by IAS have probably yet to be realized, because a worsening of the current situation is expected, both in terms of number and spread, and consequently of their likely damaging effects.…”