A Cretaceous origin for fire adaptations in the Cape flora.

Tianhua He,Byron B Lamont,John Manning

doi:10.1038/srep34880

Abstract

Fire has had a profound effect on the evolution of worldwide biotas. The Cape Floristic Region is one of the world’s most species-rich regions, yet it is highly prone to recurrent fires and fire-adapted species contribute strongly to the overall flora. It is hypothesized that the current fire regimes in the Cape could be as old as 6–8 million years (My), while indirect evidence indicates that the onset of fire could have reached 18 million years ago (Ma). Here, we trace the origin of fire-dependent traits in two monocot families that are significant elements in the fire-prone Cape flora. Our analysis shows that fire-stimulated flowering originated in the Cape Haemodoraceae 81 Ma, while fire-stimulated germination arose in the African Restionaceae at least 70 Ma, implying that wildfires have been a significant force in the evolution of the Cape flora at least 60 My earlier than previous estimates. Our results provide strong evidence for the presence of fire adaptations in the Cape from the Cretaceous, leading to the extraordinary persistence of a fire-adapted flora in this biodiversity hotspot, and giving support to the hypothesis that Cretaceous fire was a global phenomenon that shaped the evolution of terrestrial floras.

Highlights

Fire has had a profound effect on the evolution of worldwide biotas
It is hypothesized that the current fire regimes in the Cape could be as old as 6–8 million years (My), while indirect evidence indicates that the onset of fire could have reached 18 million years ago (Ma)
Our analysis shows that firestimulated flowering originated in the Cape Haemodoraceae 81 Ma, while fire-stimulated germination arose in the African Restionaceae at least 70 Ma, implying that wildfires have been a significant force in the evolution of the Cape flora at least 60 My earlier than previous estimates

Summary

OPEN A Cretaceous origin for fire adaptations in the Cape flora

Our analysis suggests that wildfires have been sufficiently intense and reliable to initiate and maintain the evolution of fire-adapted plant traits from at least 81 Ma during the Cretaceous in the Cape of South Africa, as already demonstrated in Australia with a similar fire history This is based on two monocot families with a much longer evolutionary history than the previous attempt with the orchid genus Disa[7]. It is likely that the development of fire-prone systems was not controlled by global temperatures or climate seasonality, as currently, but rather by elevated atmospheric oxygen concentrations[26] This would explain the origin and continuing evolution of some fire-dependent traits in the Paleogene-Eocene (such as serotiny in Banksia[9]; resprouting in Eucalyptus8), as higher oxygen levels would allow much moister vegetation to burn[26], and serve to decouple the relationship between fire activity and fuel-moisture levels. Biomes in the Cape and Australia are much older than the advent of their Mediterranean-type climates suggest, sharing a much earlier fire-prone history that has shaped the evolution of their floras to explain their strongly-developed fire-dependence as observed today[28,29]

Methods

Additional Information