What drives Eucalyptus globulus natural establishment outside plantations? The relative importance of climate, plantation and site characteristics

Green infrastructure design for the containment of biological invasions. Insights from a peri-urban case study in Rome, Italy

Secondary shrublands and transitional woodland/shrub formations are recognised to be particularly susceptible to plant invasions, one of the main global threats to biodiversity, especially in dynamic peri-urban landscapes. Urban fringes are in fact often the place for the sprawl of artificial surfaces, fragmentation of habitats, and complex land transitions (including both agriculture intensification and abandonment), which in turn increase propagule pressure of exotic species over residual semi-natural ecosystems. Within this framework, the present study was aimed at analysing i) how landscape composition and configuration affect the richness of woody exotic species in shrubland and transitional woodland/shrub patches, and ii) how this threat can be addressed by means of green infrastructure design in a peri-urban case study (Metropolitan City of Rome, Italy). Accordingly, the occurrence of exotic plants was recorded with field surveys and then integrated with landscape analyses, both at patch level and over a 250 m buffer area around each patch. Thus, the effect of landscape features on exotic plant richness was investigated with Generalised Linear Models, and the best model identified (pseudo R-square = 0.62) for inferring invasibility of shrublands throughout the study area. Finally, a Green Infrastructure (GI) to contain biological invasion was planned, based on inferred priority sites for intervention and respective, site-tailored, actions. The latter included not only the removal of invasive woody alien plants, but also reforestation and planting of native trees for containment of dispersal and subsequent establishment. Even though specifically developed for the study site, and consistent with local government needs, the proposed approach represents a pilot planning process that might be applied to other peri-urban regions for the combined containment of biological invasions and sustainable development of peripheral complex landscapes.

Eucalypt Recruitment and Invasion Potential in Protected Areas of the Iberian Peninsula under Current and Future Climate Conditions

Eucalyptus globulus Labill. stands have been expanding in protected areas (sites) of the Natura 2000 network in the Iberian Peninsula (Iberia). This expansion is mostly human-driven, but there is increasing evidence of plant recruitment and escape from cultivation areas. Therefore, it is important to assess the recruitment and invasion potential of sites and associated habitats and how future climate may change this potential. Here, we use SDMs to project current and future climatic suitability for E. globulus recruitment in Iberia and combine this suitability with local factors to rate the current recruitment potential of eucalypt stands. This potential is then extrapolated to neighbour areas in Natura 2000 sites to assess the invasion potential. The results show a wide recruitment range along coastal regions of western and northern Iberia (83,275 km2) and a northward contraction under climate change, similar to the trend projected for plantation suitability. Recruitment potential of any level was identified in 989 km2, while invasion potential was identified in 878 km2 across 176 Natura 2000 sites. Heathlands and riparian forests were associated with the largest recruitment and invasion potential areas. This study may help in preventing further negative impacts in protected areas and habitats already affected by E. globulus expansion.

Microsite Drivers of Natural Seed Regeneration of Eucalyptus globulus Labill. in Burnt Plantations

Fire regimes are changing in several regions of the world. In those regions, some exotic species may be better adapted to new regimes than the native species. This study focused on identifying the microsite characteristics associated with the occurrence of post-fire Eucalyptus globulus regeneration from seeds, outside the species native-range. This information is important in helping to assess the naturalization status of the species, to understand its invasion risk, and to manage wildlings in plantations. To characterize the establishment niche, pairs of microsites (sapling presence/absence) were sampled in four salvage-logged plantations of E. globulus two years after fire (20 pairs/plantation). Microsites of wildlings from three size classes and control microsites were established in one of these plantations (20 quartets) in order to characterize the recruitment niche and to assess ontogenic niche shifts. Two post-fire wildling cohorts were identified. The first emerged just after fire and was abundant. The second emerged after logging and was scarce, probably due to seed limitation. First-cohort wildlings were observed in microsites characterized by a high incidence of fire-related variables (charcoal, ash, increased soil pH and K). The aggregated distribution of these wildlings and their association with other species may indicate the existence of facilitative relationships and/or the exploitation of resource-rich patches. All these factors were relevant for first-cohort persistence and likely also for its establishment and recruitment. Second-cohort wildlings occurred in microsites where salvage-logging disturbance was evident, showing the importance of this disturbance for its emergence. Wildling size diversity was explained by the two recruitment events and by the asymmetrical competition between wildlings and adults. No niche shifts were detected. The high densities of E. globulus wildlings found established in burnt plantations indicated naturalization was in progress. The timing of major recruitment events and the phenology of the species should be considered for monitoring this regeneration and scheduling control interventions, if required.