Vulkanismus und Klima : Dynamik und Konstanz als Ursachen von Endemismus in Pflanzengemeinschaften

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Beierkuhnlein, Carl:
Vulkanismus und Klima : Dynamik und Konstanz als Ursachen von Endemismus in Pflanzengemeinschaften.
Reinhold-Tüxen-Gesellschaft
In: Berichte der Reinhold-Tüxen-Gesellschaft. Bd. 32 (2024) . - S. 183-219.
ISSN 0940-418X

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Abstract

Islands have served as natural experiments in vegetation science and biogeography since generations. Fundamental processes of speciation and coenotic organisation can be studied. Most standardized are oceanic islands of volcanic origin such as the Canary Islands. At evolutionary and geological time scales, oceanic islands of volcanic origin were subject to repeated eruptions. Strombolian type volcanism, which is widespread, produces besides lava flows also substantial amounts of pyroclastic material (ashes, lapilli, tephra) and toxic gases. In consequence, active volcanic events can affect the vegetation of a much larger area of oceanic islands compared to lava flows. The selection of specific adaptations and plant traits that support plant survival and respectively also reproduction is a process that also favours speciation and endemism. After the recent eruption of the volcan Tajogaite on the slope of Cumbre Vieja on the island of La Palma in 2021, herbs or grasses were not found on the newly created soil surface if the ash layer was more than 20 cm. However, most woody plant species populations, even though being partly damaged by sulphuric gases, persisted and were even in full flower in spring 2022 only 4 months after the end of the eruption. This applied to ash layers up to 1 m. Remarkably, such woody plants are almost completely endemics, either restricted to the island of La Palma or to the Canary Island archipelago. In consequence, I postulate that ash deposition, which is a characteristic phenomenon on volcanic islands, is selecting towards woodiness and can be one (additional) explanation of the predominance of woody plant species among island endemics not only in this case study, but also on volcanic islands worldwide. Furthermore, biotic interactions within plant communities are likely to maintain and promote plant traits such as woodiness and nitrogen fixation. Based on a revised checklist for the Canary Islands, I show that woody species and woody nitrogen fixers contribute strongly to the flora of this archipelago. The role of these species increases with naturalness, indicating that long-term evolutionary processes rather than anthropogenic drivers are responsible for this pattern.