Desert plants on the edge

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What would happen if quiver trees could migrate in a southerly direction, away from the far reaches of the Northern Cape towards the more moderate climate of the Western Cape?

The reality is that this prominent desert plant would most likely have a better chance of survival, very different from the current trends recorded in the desert biomes of South Africa. Due to increasing temperatures and less rainfall in dry regions, plants are disappearing.

“Unless we can curb global warming, we are going to lose 80% of these species,” says Barry Lovegrove, author of The Living Deserts of Southern Africa. He has noticed major changes in desert areas, including the Richtersveld, and presented his findings at the 2019 Oppenheimer Research Conference.

Quiver trees are prominent in the Richtersveld. Sketch: Graham Kearney

“I am not a climatologist, but it seems as if there has been a migration of winter rainfall to the south. This has caused an increase in the grassiness of the Nama Karoo because of a westward shift of easterly rainfall systems and a temperature increase in all the desert biomes, particularly the arid savanna,” explains Lovegrove.

Pieter van Wyk, nursery and herbarium curator at the /Ai/Ais-Richtersveld Transfrontier Park, grew up in the Richtersveld. He has witnessed the changes not only in the vegetation, but in the climate over the years. These changes are substantiated by satellite and climate data.

 

A halfmens in the Richtersveld. Photo: René de Klerk

Van Wyk says that, when easterly winds used to blow for four days or more, a low-pressure system formed and the Richtersveld received rain. For the last four years, this has not been the case. “There are plenty of warm, dry, wind and dust storms. These have possibly been the most damaging,” he says. Van Wyk confirms that, since 2012, the average rainfall in the Richtersveld has dropped by 60-90%, and temperatures are on average 2.9 degrees higher. These changes have had a massive effect on the vegetation in the region.

“Large portions of the Richtersveld plains were covered with vygies,” says van Wyk. It is estimated that 50 out of 160 genera from the Mesembryanthemaceae family occur in the Richtersveld, contributing to the region’s massive diversity. In fact, there are more than 360 flowering plant species in a square-kilometre monitoring plot in the Richtersveld. It is one of the world’s richest succulent areas, with approximately 30% of plants occurring nowhere else in the world. But there is a dark cloud over the future of these plants. “At present between 80-100% of vygies are dead in most areas,” says van Wyk. These plants act as groundcover and keep dunes along the coast stable. The dead plants will disappear in a few years, leaving open sandy areas ready for erosion.

The largest vygie in the world, Stoeberia arborea, has died in much of the Richtersveld. This is an important species that offers shelter for other small succulents. “Up to 17 lichens and two species of moss grow on them, so this loss means great damage to the environment.”

Furthermore, prominent species such as the halfmens (Pachypodium namaquanum), Helskloof aloes (Aloe pearsonii) and the three species of quiver trees are dying in mass. The quiver trees are the giant quiver tree (Aloidendron pillansii), maiden’s quiver tree (Aloidendron ramosissimum) and the common quiver tree (Aloidendron dichotomum). The small succulent beeskloutjies (Lithops herrei) no longer exists in the park, and their sudden disappearance happened while van Wyk monitored the effect of drought on the vegetation.

Helskloof aloes prominent on the Helskloof Pass in the Richtersveld. Photo: René de Klerk

“Naturally there are still seedbanks from which these species may survive, but this could be the start of long-term extinction. It takes 10-15 years for beeskloutjies to grow from seed and reach an age where they produce seed,” says van Wyk.

While all hope may seem lost for the survival of prominent plant species in the Richtersveld, van Wyk continues to discover plant species new to science. In 2019, he discovered four new species, bringing his new discoveries to 18 species.

Written by René de Klerk
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