Why are our Ana's dying?

For reasons unknown, Ana trees are dying off in the west of the country, leaving experts puzzled but with a variety of theories.

01 October 2018 | Environment

Hundreds of dead Ana tree trunks dot large areas of the Ugab, especially upriver from the Brandberg massif. In the last couple of years, scientists have established that up to 79% of Ana trees in the Swakop River have died. Scientists have witnessed the same trend in the Kuiseb River.

“Naturally it is very sad,” said prof. Nico Smit who works as a specialist in animal husbandry and grazing at the University of the Free State. “Although I have no answers, I do have several theories, because we observed a similar phenomenon in camelthorn trees,” he said.

Ana trees mainly grow in rivers and streams in the north-western regions of the country. According to the well-known zoologist Barbara Curtis, tall trees tower between ten and twenty meters in height, while the trunks of old trees can be more than a meter in diameter. The taproot also grows up to 40 meters below ground, consequently these trees can easily tap water from aquifers in rivers.

“In a survey carried out in the Swakop River, students from Gobabeb found that between 67% and 79% of trees there had died, in comparison to 4% in the Kuiseb,” she said. The students also found no cause for the die-back. “Perhaps it could be that the groundwater level has sunken. This could be true in the Swakop River because there are many dams and boreholes along its course, but it cannot be the case in the Ugab,” she said.



Old age?

According to Smit, “Many of these trees, which died in a relatively short period of time, are quite old and are most likely of a similar age”.

These trees grow in dry riverbeds and could have survived repeated years of extreme or unfavorable environmental conditions, including droughts. “However, in time these trees are no longer able to survive in these harsh conditions given their age or natural senescence,” he explained.

In this context, he recalled a long and especially severe drought that hit large parts of southern Africa a few years back. Consequently the groundwater in some rivers have fallen substantially. However, he is convinced that younger trees would have survived this, describing such extreme conditions as normal because it happens ever so often.

“Because of climate change, however, such extremes are aggravated and more extreme. It is striking that between the old, dead trees, no young trees seem to grow,” he said. Since no younger trees are replacing the old ones, the die-backs are particularly noticeable, according to Smit.

In addition to this theory, Smit can't rule out an infection, such as a fungal disease, that could have contributed to the trees dying.

Well-known Namibian botanist Coleen Mannheimer sees it in a similar light. “I think it's a fatal combination of a high parasite infestation and drought that has weakened the trees,” she said. “It is cause for concern.”

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