Determinants of naturalization and invasion of Tetraclinis articulata in eastern Mediterranean drylands: Is it a “superinvader”?

Abstract Tetraclinis articulata, endangered in the western Mediterranean, is suspected to have become invasive in the eastern Mediterranean. This study assessed its naturalization/invasion status across Israel, where it was planted over 6000 ha in semi-arid and Mediterranean regions. We hypothesized that T. articulata colonizes undisturbed sites with low competition in combination with favourable microhabitat conditions for germination and establishment. We measured the density of regenerating T. articulata saplings in 46 eastern Mediterranean plantation sites up to 60 m away from plantation margins. Saplings were observed in 74% of the sites, of which 79% contained saplings beyond the plantation margins. The density of saplings decreased with distance from the margins and was significantly higher in Mediterranean than in semi-arid sites. Higher sapling densities were associated with tall, dense, woody vegetation formations, northern hillslope aspects with moderate slopes, soft bedrock, high stone/rock cover and absence of livestock grazing. We found that microclimatic refuges act as stepping stones for seedling recruitment, potentially explaining the successful colonization by this slow-growing species in dryland climates. Contrary to the common invader archetype, T. articulata exhibits late successional characteristics, preferentially establishing in well-developed woodlands and forests, in line with the recently defined “superinvader” archetype. Exhibiting superinvader behaviour, the invasion potential of T. articulata in natural eastern Mediterranean dryland ecosystems poses a serious threat. Reducing seed sources regionally, including drastic action such as clearing mature forests to protect biodiversity, is vital to preventing spread, especially in Mediterranean climates, and near woodlands. In the larger scheme of things, afforestation efforts in drylands using exotic drought-resistant tree species must consider this potential outcome.