BayCEER Workshop 2023

Only the tough are good enough – about ancient lapilli fields and selection towards insular woodiness

Due to their unique properties, islands are perceived as “evolutionary arenas”. Multiple distinct life forms evolved on islands, so-called island syndromes. One of which is the evolution of woodiness in otherwise herbaceous lineages, observable on different islands globally. This insular woodiness is a special form of secondary woodiness and closely related with the dispersal of a taxon to an island. Multiple hypotheses emerged trying to explain the mechanisms leading to this evolutionary convergence. These hypotheses are linked to competition, drought, stable climate, herbivory, and longevity. However, currently for none of these exists compelling experimental evidence. Recently a new hypothesis emerged, linking volcanic activity and the consequential burial of vegetation through tephra depositions to the evolution of wood on islands. Volcanic eruptions and consequential burial – as an abiotic filter – happen frequently on evolutionary timescales. Small, herbaceous plants are therefore removed frequently from the community and woody plants are selected. On volcanic islands, all ecosystems are shaped by volcanic activity, to varying impact, however. Ancient lapilli fields are strongly shaped by lapilli depositions, a pyroclastic material between 2 and 64 mm. On these fields the potential selection factor of lapilli burial is strongly established, and these fields are dominated by woody plants. Furthermore, especially younger lapilli fields are also dominated by insular woody plants. Studying these ecosystems may be crucial to understand the evolution of insular woodiness.

Ancient lapilli fields on the island of La Palma, Spain.