Understanding recruitment limitations in a critically endangered species: The story of the iconic Cape cedar (Widdringtonia wallichii)

Abstract

Demographic modelling predicts the critically endangered Clanwilliam cedar (Widdringtonia wallichii), an iconic conifer of South Africa, to be headed for extinction. Due to an apparent mismatch in life-history traits with the local fire regime, such as time to reproductive maturity exceeding mean fire return intervals and no clear seed dispersal agent, it is considered poorly adapted to its fire-prone environment.Here we focus on two key demographic knowledge gaps, seed dispersal and germination, and suggest cedars are highly adapted to wildfires. Our natural history observations show that seeds are scatterhoarded by the Cape spiny mouse (Acomys subspinosus) to safe sites that are optimal for germination. In many cedar sites spiny mice are absent, scatterhoarding has collapsed, and seed predation by the Namaqua rock rat (Micaelamys namaquensis) is most frequently observed. Additionally, seeds are fire-stimulated. However, 85% of trees experienced ca. 70% of their fires before annual seed fall, limiting recruitment opportunities.Our results suggest the cedar is strongly fire-adapted, and that the main demographic hurdle presently is not high adult mortality in fires but poor post-fire recruitment. Consequently, conservation emphasis should be on increasing recruitment rather than mitigating adult mortality. We suggest the following conservation measures: i) prescribed fires after seed fall (i.e. late autumn) to allow for scatterhoarding by rodents, ii) artificial burial of pre-heated seeds in burned stands in late autumn to optimise recruitment, and iii) planting locally dense stands of seeds/seedlings to guarantee predator satiation of seeds and thus strongly establish the scatterhoarding mutualism required for effective recruitment.

Keywords

• Plant demography
• Fire-stimulated germination
• Fire regime
• Mutualism
• Scatterhoarding
• Seed dispersal