Augrabies’ quiver trees under threat

The quiver tree, Aloe dichotoma, is an iconic plant species and their distribution limited to the blistering, stony semi-desert areas in the Northern Cape and southern Namibia where they are a conspicuous feature of the landscape. It is believed that they are under threat due to changing climatic conditions including global warming.

They are slow-growing and very susceptible to damage due to the extremely fibrous structure of the wood. Large specimens could possibly be as old as 250 years. If quiver trees are not able to cope with less rain and higher temperature, which is an imminent threat in their current distribution range, they might become extinct locally.

In the Augrabies Falls National Park it was noted that an unacceptable level of damage was caused by antelope including giraffe, eland, kudu and gemsbok. There are numerous reasons why herbivores do this. They could be feeding on the leaves, using trees for shade, getting rid of ectoparasites or just putting pressure on the stems by leaning against them.

When branches break, very little resprouting, which ensures continued growth and the production of seeds, takes place compared with other plant species. Young trees are often so badly damaged that they die.

Quiver trees most probably did not evolve being subjected to damage by antelope species on a continued basis, and therefore cannot cope with this persistent pressure.

In order to keep the animals from damaging the trees it was decided to build an enclosure camp consisting of six kilometres of fencing surrounding an area of 210 hectares. This informed decision was made after 100 individual plants were surveyed annually starting in 2011, with the third survey in 2013.

Some of the trees being monitored are outside the camp with the remaining ones fenced in. Interesting comparisons will now be possible between the individuals being protected from herbivores and the ones that are still exposed to the threat posed by the antelope.
Financing for labour for erecting the fence was generously donated by the West Rand branch of the honorary rangers.