Veld & Flora Feature
This article is a SNEAK PEEK from Veld & Flora’s September 2021 edition,
which will be out next week.
Rediscovering a forgotten forest
On the border between KwaZulu-Natal and Mpumalanga, Pongola Bush has withstood natural and human onslaughts for more than 2 million years.
SEP 22, 2021 | BY TIMOTHY HALL & ROBERT SCHOLES PHOTOGRAPHS: TIMOTHY HALL
Above: Timothy Hall surveys the Pongola Bush.
NESTLED AGAINST THE CRAGS of the highveld escarpment that form the boundary between Kwazulu-Natal and Mpumalanga is a band of forest. It is nearly 20 kilometres long but only a few hundred metres wide.
This is the Pongola Bush, a remnant of Afromontane forest with a rich history, both in evolutionary time and over the past two centuries. The name is pragmatic – it lies near the source of the Phongolo River and uses the old Dutch word bosch, meaning forest.
Like most scarp forests, Pongola Bush is south facing, giving it a cooler and wetter microclimate than north-facing slopes. Clouds often gather against the mountain, contributing to the precipitation of 1 000 millimetres per year that this kind of forest needs in order to survive.
Above: This clearing in the Pongola Bush suggests there might be an ‘old lost road’ through the woods.
Even in wet areas, indigenous forest patches survive only where they are protected from fire – in this case, by the rugged cliffs at the back of the forest.
European settlers devastated the forest in the late 19th century to feed the mining boom. Giant yellowwood trees were felled, sawed into planks and transported by ox wagon to distant markets.
They were used to build Barberton, where in 1874 gold was first found in South Africa. Later, timber from the Pongola Bush also built the early Witwatersrand structures. Today the greatest threat is faced by the closest large forest patch, Paardeplaats Reserve, about 10 kilometres northeast in Mpumangala. There are ongoing attempts to remove its protected status, as well as those of the wetlands that give rise to the Phongolo, Usutu, Thukela and Vaal rivers and the species-rich Paulpietersberg grasslands so that new coal mines can be established.
Left: The rare yellow shell-flower bush, named Bowkeria citrina after James ‘Butterfly’ Bowker (1828-1900), is found only in this area. Right: The velvet worm is a living fossil of ancient lineage that lives only in leaf litter or rotting logs in moist forests.
SCIENCE MOVES IN
In 1904, an expedition from the Natural History Museum of London visited the Pongola Bush to collect specimens. They recorded Cape parrots, which live mainly on the fruits of yellowwood trees (Afrocarpus species, formerly known as Podocarpus). Cape parrots are no longer found in the wild in northern KwaZulu-Natal.
The eccentric plant collector Justus Thode (1859-1932) worked as a tutor on a nearby farm between 1920 and 1924 and used his spare time to explore the area. As a result, he was responsible for much of what we know about Drakensberg plants in the early 20th century.
He described the beautiful yellow shell-flower (Bowkeria citrina). This three-metre-high shrub is a very narrow endemic, occurring only in the rare forest subtype of the Pongola Bush and surrounding forest patches.
That is not the only special species from the forest, which still has been only poorly explored scientifically. After the last large fragment of the Pongola Bush was acquired for conservation by the Natal Parks Board in 1972, several brief visits by a range of specialists contributed to a species list of:
- About 174 plants, 10 of which are rare or endangered
- A bird list of around 120 species
- Three millipede species known only from the location, although they may also occur in nearby forests
In 2019, Dr Michele Hammer found specimens of the velvet worm (Onychophora). This small slug-like creature is a living fossil of ancient lineage, restricted to the floors of moist forests, where it lives in rotting logs or leaf litter. It is quite unable to travel between separate forest patches.
The velvet worm’s dilemma suggests that the Pongola Bush is a remnant of an even more extensive forest that may have occurred along much of southern Africa’s eastern escarpment. Over the past 50 million years, however, Africa has slowly dried out. About 8 million years ago fires began having a prominent impact on the landscape.
The more recent pleistocene era, from nearly 3 million years ago to about 12 000 years ago, probably prompted this huge escarpment forest to break up into patches. Climate during the pleistocene regularly fluctuated between ice ages and climate similar to our present one.
During the wetter, warmer periods between ice ages, the forest patches may have expanded and possibly joined up in some instances – only to be torn apart in the next cold, dry glacial period. It is thought that this pattern of isolation and remixing the gene pool encourages new species to evolve.
The likely dates for the heyday of this region’s forests and their fragmentation long precede the evolution of humans. There is evidence of very early modern humans living as long ago as 200 000 years at Border Cave in the Lebombo Mountains, about 100 kilometres away. People with cultural features of the San occurred in the Pongola Bush area from about 44 thousand years ago up to about 160 years ago.
There is no evidence, however, for suggestions by vegetation ecologist John Acocks (1911-1979) among others that around 2 000 years ago, when settled Bantu-speaking agro-pastoralists and iron-workers arrived, their impact converted a hypothetically continuous eastern escarpment forest into its present archipelago of tiny patches. Similarly, European settlers found the forest already in patches, before reducing its resources significantly from the late 19th century onwards.
Above: This aerial shot shows how the Pongola Bush hugs the highveld escarpment.
ON THE GROUND
In July 2020, University of the Witwatersrand honours student Timothy Hall spent a week doing the first comprehensive assessment of the forest trees’ biomass and diversity. He divided the main, 882-hectare protected patch into 127 study plots of 80 square metres each. He then counted, identified and measured all the stems in each plot.
Quite apart from the saw-pits and decaying stumps, the forest told its own tale of timber over- exploitation a century or more ago. Timothy encountered no large individuals of valuable timber species, although a few large trees are known to persist in inaccessible corners.
The four dominant canopy species – red currant (Rhus chirendensis), forest bushwillow (Combretum kraussii), wild peach (Kiggelaria africana) and white stinkwood (Celtis africana) – are typical of forests recovering from disturbance.
Above: The forest looks all the more dense against its surrounding grassland.
The forest trees’ average biomass above the ground was about 70 tonnes per hectare. This is typical of escarpment forest patches, but about a third of what would be expected in a tall, unharvested Afromontane forest.
Timothy recorded 47 tree species, which suggests a total of perhaps 70 tree species would be recorded by an exhaustive survey. This extrapolated figure agrees quite well with lists compiled by various collectors over the years. The number of herbaceous species is less well established but is probably at least as many.
There are encouraging signs of forest recovery in the Pongola Bush. Many small and medium-sized individuals of tree species occur and will eventually form part of the canopy, such as the Outeniqua yellowwood (Afrocarpus falcatus). Perhaps one day the Pongola Bush will ring to the calls of the Cape parrot once again.
Timothy Hall is a now a master’s student at the University of the Witwatersrand. The late Robert Scholes (1957-2021) was professor of systems ecology and director of the Global Change Institute, University of the Witwatersrand.
Officially, the names of the Phongolo River and municipality have been updated but the Pongola Bush Nature Reserve retains the old spelling.
Pongola’s timber trade
Founding Pongola’s timber trade in the mid-19th century, several groups disputed control of the rugged Pongola escarpment region between the present-day towns of Wakkerstroom and Mkhondo (previously Piet Retief). The escarpment formed a fluid, poorly defined frontier between the Zulus to the east, the Swazis to the north and the Boers to the west.
From 1860, the Zulu king Mpande saw advantage in allowing German missionaries to settle in the area. They formed a village that became known as Luneburg. Artisans accompanied the missionaries because a large element of German mission activity involved training in the trades. When missionary-society funding ran out soon after the party arrived, the settlers obtained a concession from the Zuid Afrikaanse Republiek government to harvest timber from the nearby Pongola Bush.
How to measure a forest
An ecosystem’s species diversity is calculated by plotting the ground area where specimens have been identified against the number of species encountered. This is called the species-area curve, which typically levels off gradually as the area sampled approaches the ecosystem’s total area.
When the data are plotted as a logarithm, they form a fairly straight line. In the case of Pongola Bush, the line’s slope is similar to some other southern African ecosystem types and particularly to other forest fragments of various sizes in the escarpment and Drakensberg region. This finding confirms how rich in species South Africa’s forest patches are and emphasises their conservation importance, even though they are a small part of the landscape.
This article was first featured in Veld & Flora in the September 2021 edition. Veld & Flora is only available to BotSoc members.
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