Volcanic deposits select for woodiness on islands

Oceanic islands’ unique biodiversity often arises from woody plant radiations derived from non-woody continental ancestors. Since Darwin, various theories have tried to explain the evolution of woodiness on islands (insular woodiness). Recently, frequent volcanic activity and burial of vegetation by volcanic ash (tephra) depositions were linked to the abundance of woody species on islands. In a chronosequence of five tephra fields on the island of La Palma (Canary Islands), we found a trend towards woody growth form, providing first evidence that volcanism favors woody species. Endemic insular woody species prevail on young fields, whereas woody species with woody colonizers become dominant on older fields. High similarity in functional traits is detected between fields. This highlight that endemic insular woody species show increased colonization and establishment ability on extreme habitats after volcanic eruptions, illustrating acquired functional advantages of endemic lineages that evolved woodiness on islands and sheds light on the role of environmental filtering during evolution.