Only the tough are good enough - Evidence for selection towards insular woodiness on ancient tephra fields

Simon Biedermann1, Anna Hollweg1, Anna-Maria Seiverth1, Lena Wege1, Trevor Roberts1, Nicolai Nürk2, Alessandro Chiarucci3, Carl Beierkuhnlein1
1 Biogeography, University of Bayreuth
2 Plant Systematics, University of Bayreuth, Bayreuth, Germany
3 Department of Biological, Geological, and Environmental Sciences, University of Bologna

P 6.6 in Posters

Secondary woodiness that originates on oceanic islands, insular woodiness, is a
remarkable island syndrome that evolved independently throughout the angiosperm tree
of life. One of several hypotheses explaining this phenomenon states that burial of
vegetation through tephra from volcanic activities on the island is a selecting driver
towards insular woodiness. However, there is currently no conclusive evidence for this
hypothesis.
Here, we test the role of volcanic tephra deposits as a driver for insular woodiness by
analysing vegetation patters and plant functional traits related to five craters that
erupted in historic times on the island of La Palma.

Vegetation on lapilli fields is dominated by secondary woody and archipelago-endemic
woody species, with younger tephra fields highly dominated by secondary woody species and older fields more dominated by ancestral woody species. Furthermore, the functional
trait space seems constraint in lapilli vegetation in comparison to pine forest in the same
elevation range. These observed patterns indicate potential abiotic filtering of tephra
burial towards (insular) woody species and their traits. Our results thus provide the first
empirical evidence for the “volcanic selection” hypothesis of insular woodiness.

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