Is an invasive alien tree able to sustain a similar lichen diversity as the native forest? The case of the sweet chestnut (Castanea sativa Mill.) and the Laurel forest in Macaronesia.
Invasive alien species are considered as one of the major threats to global biodiversity. Many widely used forestry trees are potentially invasive, spreading from planting sites into adjoining areas modifying community composition, and altering the native forest. In the Canary Islands, Castanea sativa was established half a millennium ago, in the distributional area of the laurel forest, an endemic forest of the Macaronesia. The impact of invasive species on ecosystem services and more specifically their impact on epiphytic lichens is totally unknown in these archipelagos. The main aim of this work has been to find out if the chestnut tree can host an analogous species composition, richness, and diversity of epiphytic lichens such as those present in the native forest from the Canary Islands. Whilst species richness in both habitats is high, the composition is significantly different. The characteristic species were also different. The chestnut tree hosted rare species linked to ancient and well-preserved forest environments. For this reason, we propose not to completely eradicate the chestnut tree in the Archipelago, but we consider the management and control of its expansion to be essential. Preserving ancient specimens can serve as a lichen biodiversity reservoir.