Behind the scenes of the palm invasion in Southern Switzerland: ecological, functional and societal dimensions of a banned iconic species in a shifting biome

Novel ecosystems driven by non-native species increasingly challenge classical conservation and management paradigms, particularly when ecological change intersects with cultural values. In the lake-rich Insubric region along the Swiss–Italian border in the southern European Alps, the naturalization of the iconic Chinese windmill palm (Trachycarpus fortunei) is part of an ongoing biome shift toward mixed evergreen, laurophyllous forests. To understand the multi-dimensional implications of this process, we synthesized results from complementary ecological, functional, and socio-cultural studies.

We surveyed forest vegetation, quantified arthropod communities in paired invaded and non-invaded stands, measured litter decomposition, assessed fire behavior and post-fire stand dynamics, documented the establishment of the palm borer moth Paysandisia archon, and conducted a nationwide public perception survey. Together, these approaches allowed us to evaluate how T. fortunei reshapes biodiversity, ecosystem processes, disturbance interactions, and social attitudes.

Vegetation surveys revealed that high palm densities markedly reduce the richness of native recruiting tree species in alluvial forests, whereas effects on mixed broadleaved forests on slopes remain minimal. Arthropod communities shifted, with herbivore richness declining, likely due to reduced understory plant diversity and the low nutritional quality of palm foliage. Despite the slow decomposition of palm leaves, overall litter decomposition increased with palm abundance, suggesting microclimatic or decomposer-mediated changes. Filamentous palm roots likely provide limited slope reinforcement, offering little protection against shallow landslides. Fire assessments showed that adult palms are highly fire-resistant, yet their flammable stem-attached fuels and dry leaves can increase fire intensity and channel flames upward, causing greater damage to neighboring deciduous trees than to the palms themselves. Meanwhile, P. archon established in southern Switzerland, posing a threat to cultivated palms and potentially limiting the spread of naturalized T. fortunei. Public perception data revealed strong regional differences in attitudes toward palms, with cultural associations in southern Switzerland reducing support for control measures, although this changed markedly when ecological impacts were communicated.

Together, these studies provide a holistic assessment of the ecosystem functions and disservices of an iconic but invasive species at the center of a regional biome shift, underscoring the need for adaptive, context-specific, and socially informed management strategies for novel ecosystems.