Tracking the survival of Quiver trees
WHILE CLIMATE WARMING AND RESULTING DROUGHTS ARE CAUSING DECLINES IN THE HEATSTRESSED
NORTHERN POPULATIONS OF QUIVER TREES, THOSE IN THE HEAT-LIMITED SOUTH BENEFIT
Quiver trees, Aloidendron dichotomum, appears to be undergoing the early stages of a range shift in response to anthropogenic climate change in south-western Africa (Photo: Wendy Foden).
Sites like Kokerboomkloof in the Richtersveld attract visitors with the beautiful quiver tree, an icon of our arid parks. Quiver trees play a key ecosystem role, often providing the only bird perches and nesting sites in an otherwise treeless landscape. They are also an abundant source of nectar during their flowering. But these giants are strongly impacted by climate change and are declining markedly in their northern distribution, including central Namibia, the Namib, Richtersveld and along the Orange River. As large, resilient, long-lived and widespread species that are far less sensitive to change than smaller, small-ranged species in their habitats, quiver trees provide a conservative indicator of climate change impacts in our arid ecosystems.
As part of a long-term monitoring programme set up in 2002, a team from Stellenbosch University and I are returning to 41 quiver tree populations across the species’ range to track changes in their abundance and health. Using a combination of tree measurements, repeat photographs and population trends, this research allows us to document and validate climate change impacts and predictions which are unprecedented in Africa.
Our research team is focusing on aspects such as population genetics, stress eco-physiology and palaeo-history, and are slowly uncovering the survival mechanisms and ecology of this mysterious desert giant.
Initial findings offer hope for the species’ survival in their southern range. While climate warming and resulting droughts caused declines in the heat-stressed northern populations, those in the heat-limited south have benefitted. Research co-led with Kerry Grey and Guy Midgley examined the eco-physiological responses of quiver trees to cold, finding that their CAM photosynthetic strategy requires a degree of warmth that is now increasingly available. This means that quiver trees in Meerkat and Namaqua National Parks, as well as in iconic sites such as Ganabos in Nieuwoudtville and the Kamiesberge, are persisting and even expanding their range. Just seven more sites require assessment before the conclusion of this decade’s monitoring, whereafter analyses will reveal the status of the species and the likely future of this and other desert succulents under climate change.
This article was originally published in the 2022/2023 Research Report.
This article is based on a publication in Journal of Experimental Botany
Grey K-A, Foden W and Midgley GF. 2022. Bioclimatic controls of CO₂ assimilation near range limits of the CAM succulent tree Aloidendron dichotomum, Journal of Experimental Botany, 73 (22), 7434–7449.
