The secret treasure trove still hidden in Africa’s forests

The ‘last biotic frontier’ lies hidden right above our heads in the continent’s fascinating tree canopies.

It’s 8am on a Tuesday and Rudi Swart, 33, is getting ready for yet another day in the office. After tossing his work bag in his car, he picks up his colleague – experienced rock climber, Matthew Kingma – from his home in the South African town of George. From there it’s a 20-minute drive to the Groenkop Forest parking area, and a 25-minute walk to the 17-metre (55-foot) assegai tree (Curtisia dentata) Swart – who himself measures 1.94 metres (6.36 feet) – will be climbing today.

Before climbing the tree, they need to throw a rope with a weighted end over a suitable branch. This is a frustrating process that can take up to an hour of trying, but today they are in luck: Kingma scores a perfect strike on his fourth attempt. Once the rope is around the branch, they pull it down and use it to take a second rope to the top of the tree. Swart attaches one of the ropes to his harness and climbs the other one, while Kingma waits at the bottom and makes sure his charge cannot fall. “You feel it in the legs, not the arms,” says Swart, with a diffident laugh. “When I started, I was slow. But now I can get up a tree in about 10 minutes.”

After making himself comfortable on a branch with a good view of a clump of the assegai’s small, off-white flowers, Swart gets to work. Over the next four hours he makes a note of every creature that visits the flowers, and he tries to catch at least one sample of each different species. He also takes hourly temperature and wind speed (he brings a portable anemometer up the tree with him!) recordings. Kingma, meanwhile, sits on the forest floor and waits …

The next day, weather permitting, they will do it all again. Because when you’re part of a tiny band of people who are trying to understand the secret world above our heads, there is little time to waste. Despite being priceless biodiversity hotspots and carbon sinks, Africa’s Indigenous forests remain one of the most poorly understood biomes in the world.

All told, Swart did 36 climbs (24 diurnal and 12 nocturnal) up 24 different individual trees of six common species in Groenkop. Across 144 observation hours, over a four-month period between September 2021 and January 2022, he recorded 105 different insects and invertebrates. Of these, two new hoverflies have been formally described by John Midgley, a hoverfly expert based at the KwaZulu-Natal Museum. It’s hard to say how many more undescribed species Swart may have found: identifying new species and working out how they fit into the ecosystem is both expensive and time-consuming. That’s why, globally, only 10-20 percent of insects have been described.