Is the geographic range of the desert tree, Aloidendron dichotomum, shifting in response to climate change?

Prof Guy Midgley1, Ms Kerry Grey2, Prof Wendy Foden3

1Stellenbosch University, Stellenbosch, South Africa, 2University of Cape Town, Cape Town, South Africa, 3South African National Parks, Cape Town, South Africa

The desert tree succulent, Aloidendron dichotomum, occupies a large geographic range stretching between southwestern South Africa and northern Namibia, encompassing both summer and winter rainfall regimes. This is a region that has seen significant warming over the past few decades, leading to apparent demographic shifts in populations throughout the range. We will explore whether these shifts might be linked to anthropogenic climate change, both by reviewing already published work, and by presenting new results on reconstructed  paleo-range shifts and contemporary physiological and demographic responses at key sites. Our evidence suggests that a range shift may be underway, with populations declining in warmer and drier parts of the range, and expanding in cooler parts of the range. The pattern of change is more complex than can be represented by either a latitudinal relationship (although latitude provides a powerful hint for attribution), or a dichotomy between summer and winter rainfall population responses. The long lifespan of the species complicates attribution of observed mortality patterns to anthropogenic climate change, but patterns of population expansion may provide valuable evidence of a climate change driver of range shift.


I have engaged in climate change related research since the 1980s, as a researcher with the South African National Biodiversity Institute, mainly in the field of plant ecology and ecophysiology. I have worked on plant species responses to elevated CO2, applied niche based modelling methods to conduct biodiversity risk assessments, attempted to synthesize dynamic population level processes with simple niche based approaches, and explored the interactive roles of disturbance and climate change in driving ecosystem level changes. I have participated in numerous IPCC assessments, and at the national level have helped to develop broad conservation approaches to adapt to climate change. I took up a professorship at Stellenbosch University in 2014 and now engage mainly in species level work on climate change with a physiological and demographic perspective, and the links to system level responses at landscape level through modelling and remote sensing approaches.

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The conference brings together scientists and natural resource managers working in the disciplines of global change, biogeography and evolution, and relevant in contexts of natural resource management, biodiversity management and conservation, and theoretical ecology.

Species responses to climate change is a rapidly evolving research field, however, much of our progress is being made in independent research areas: e.g. understanding the process vs responding to the implications, terrestrial vs marine ecosystems, global meta-analyses vs in depth species-specific approaches. This interdisciplinary conference develops connections between these parallel streams, and across temporal and spatial scales.

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