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The Quiver Tree - threatened by encroaching desert

With a stocky trunk topped by a tangle of forked branches, Aloe dichotoma is well known in Namibia and South Africa, where its turquoise crown stands out against dry and dusty landscapes. Bushmen have traditionally used its hollow branches to make quivers for their arrows, giving its popular name 'Quiver tree'.

Quiver tree Aloe dichotoma, Northern Cape Province,
South Africa. © Caroline Auzias

However, in Africa's Northern Cape, findings from a study by the South African National Biodiversity Institute (SANBI) strongly suggest that the range of the Quiver tree has begun to respond to climate-induced stress. Observations from over 50 sites in the trees range noted two trends. Firstly, where populations were found on slopes, mortality was much higher at lower elevations than at higher ones (where it would be warmer). Secondly, there were higher mortality rates in the north of the tree's range (towards the equator), than those found in the south -again, trees survived better where the climate was cooler. Weather stations in its range showed rising temperatures throughout the past few decades, and models predict that in the future the range of A.dichotoma would contract, unless the tree was able to disperse into new, cooler, regions.

However, in Africa's Northern Cape, findings from a study by the South African National Biodiversity Institute (SANBI) strongly suggest that the range of the Quiver tree has begun to respond to climate-induced stress. Observations from over 50 sites in the trees range noted two trends. Firstly, where populations were found on slopes, mortality was much higher at lower elevations than at higher ones (where it would be warmer). Secondly, there were higher mortality rates in the north of the tree's range (towards the equator), than those found in the south -again, trees survived better where the climate was cooler. Weather stations in its range showed rising temperatures throughout the past few decades, and models predict that in the future the range of A.dichotoma would contract, unless the tree was able to disperse into new, cooler, regions.

However, in Africa's Northern Cape, findings from a study by the South African National Biodiversity Institute (SANBI) strongly suggest that the range of the Quiver tree has begun to respond to climate-induced stress. Observations from over 50 sites in the trees range noted two trends. Firstly, where populations were found on slopes, mortality was much higher at lower elevations than at higher ones (where it would be warmer). Secondly, there were higher mortality rates in the north of the tree's range (towards the equator), than those found in the south -again, trees survived better where the climate was cooler. Weather stations in its range showed rising temperatures throughout the past few decades, and models predict that in the future the range of A.dichotoma would contract, unless the tree was able to disperse into new, cooler, regions.

Not only does this study highlight the implications for the species A. dichotoma, but it also indicates that biodiversity in desert ecosystems may be under threat from climate change, even though they are already relatively hot and dry. This may be especially important when combined with the increasing trend to desertication, caused by inappropriate and unsustainable land uses.

Find out more by reading the journal 'Nature':

Cherry, M. (2005). Ministers agree to act on warnings of soaring temperatures in Africa. Nature 437, 1217-1217 (27 Oct 2005) (access restricted to subscribers).



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