Insular woodiness - the evolutionary transition from herbaceousness toward woodiness in plant species on islands - is common on oceanic islands, yet its drivers remain debated. A recent hypothesis proposes that volcanic deposits (tephra) acts as a selective mechanism promoting the evolution of woodiness in flowering plants. Here, we test this hypothesis on the island of La Palma (Canary Islands, Spain) by comparing plant communities on recent tephra depositions in the volcanically active south with the volcanically dormant north. We surveyed 132 vegetation plots in two of the island’s major ecosystems, the Canary pine forest and the succulent scrub. We recorded species richness, cover, and woodiness type: woody island species with woody continental ancestors vs. insular woody species stemming from herbaceous continental ancestors. When controlling for climatic differences, we found that woody species, particularly endemic, insular woody species, were significantly more common in the southern than the northern succulent scrub. In contrast, the Canary pine forest ecosystem showed no significant north–south differences regarding woodiness. This discrepancy may be due to both the generally low understorey species richness of the Canary pine forest and the frequent pine forest fires, which limit the potential for detectable shifts in woodiness. These patterns are consistent with the hypothesis that long-term volcanism may influence the evolution of woodiness on islands and local plant communities, but this effect is mediated by ecosystem type.

island biogeography, island syndromes, tephra, selection, Canary Islands