Ensemble modeling to predict current and future distribution of Ailanthus altissima (Mill.) Swingle in Tunisia

Ailanthus altissima (Mill.) Swingle (# AILAL) is a significant invasive alien plant (IAP) in the Mediterranean Basin. It was introduced in Tunisia as a street ornamental tree and became naturalized in several urban cities. Thereby, predicting its potential geographic distribution can provide theoretical support for managing its spread. A biomod2 ensemble model (EM) was used to forecast its potential geographical distribution in Tunisia; explore the environmental variables shaping its distribution; estimate its ecological niche dynamic; and understand its migration trajectory under future scenarios. The simulation trials selected four optimal species distribution models: Random Forest, Maximum Entropy, Generalized boosting model and Artificial neural networks. EM increased the precision of fitting and decreased the uncertainty of fitting generated by single models. The mean TSS, and AUC values for the EM were 0.996 and 0.999, respectively. AILAL potential distribution is largely influenced by built-up areas, precipitation of the coldest quarter, grassland areas and mean temperature of wettest quarter. It is well adapted to occur in built-up areas, its natural regeneration was positively associated with dense urban areas and it decreases with the increasing of grassland range areas. It requires an optimal precipitation of 200–600 mm in the coldest quarter, a precipitation of 40–80 mm in the warmest quarter and an optimal temperature in the wettest quarter of 8–11 °C. Its most suitable geographical area in Tunisia is the northern part. Under future climate conditions, these areas are at a high risk of AILAL invasions. Notably, its highest predicted expansion, under the scenarios SSP2.6, is about 140%, 150%, 128%, and 139% for 2030s, 2050s, 2070s and 2090s, respectively. For the SSP8.5 scenario, its expansion could reach about 137%, 142%, 119%, and 74%, respectively. Accordingly, management, control and surveillance actions should focus on the northern part of Tunisia to avert the spread of AILAL.