Natural forests combat non-native tree invasions

The native biodiversity of natural forest patches like this one in the foreground play a crucial role in buffering against invasions by non-native plants and trees, while the non-native eucalypt plantation in the background provides the timber resource for countless products. Good land management is required to ensure that the non-native eucalypts fulfil their function, while the natural forest, which harbours the biodiversity that underpins a healthy landscape, needs to be carefully protected.

A new study, published recently in Nature, has found that the native biodiversity of natural forests largely buffers the severity of non-native tree invasions.

The bad news, however, is that humans remain mostly responsible for introducing non-native tree species to an area in the first place – either intentionally or accidentally.

These are two of the key findings from a global study to determine the relative importance of human activity, environmental conditions, and biological diversity as drivers of tree invasions worldwide. The study, titled “Native diversity buffers against severity of non-native tree invasions” was published in the journal Nature on Wednesday, 23 August 2023.

Prof. Cang Hui, holder of the South African research chair in mathematical and theoretical physical biosciences at Stellenbosch University (SU), and one of the co-authors of the study as part of the Global Forest Biodiversity Initiative (GFBI), says trees are exposed to a wide range of ecological and human factors, and tree invasions are both drivers and passengers of global environmental changes.

This is because of their size, long life span and important role in forestry, foraging, city landscaping and reforestation, as well as carbon sequestration and climate regulation. Yet invasion biologists have long been struggling to identify the ecological mechanisms driving the invasion success of a small portion of non-native tree species.

Their findings support the biotic resistance hypothesis, which holds that greater diversity in the native community will fill the ecological niches and reduce available resources, thereby limiting non-native species to take up niche spaces.

The prominent role of human activities, however, came as a surprise: “Our findings suggest that human activity may overwhelm ecological drivers of invasions and even reduce the influence of ecological processes,” he warns.

Three of the most frequent non-native trees in the GFBI database (left to right) Black Locust; Osage orange; Tree of Heaven (Photos courtesy iNaturalist, Dave Richardson, Rosario, and Gehardt).

Repeated human introductions of plant species, especially close to ports and airports, play an important role in the initial introduction process. The severity of the invasion, however, is predominantly a result of the intrinsic diversity of the native community.

It is therefore important to conserve natural forests to maintain high native tree diversity, they write in the paper.

Furthermore, because many tree species are introduced purposefully for forestry or to support local livelihoods, they recommend that local stakeholders are included when making decisions about how best to benefit from these managed forests.

Some of the other findings include:

Read the full article here: Delavaux et al. (2023) Native diversity buffers against severity of non-native tree invasions

Joy as pepper-bark trees come back from the brink

FSA’s Nathi Ndlela and small-scale grower Rejoice Shozi hand over prized pepper-bark trees to the Dube Traditional Council and community members.

Forestry South Africa (FSA) has distributed rare and endangered pepper-bark trees (Warburgia salutaris) grown by the Warburgia Programme to schools, traditional healers and forestry community leaders, in celebration of Arbor Week.

This is in support of a highly successful initiative to propagate and re-establish this important indigenous tree which has become highly endangered throughout southern Africa due to rampant harvesting of its bark for use as traditional medicine.

Warburgia salutaris, commonly known as the pepper-bark tree or ‘isibhaha’ in isiZulu, is renowned for its medicinal anti-viral, anti-bacterial and anti-fungal properties. The bark of the tree has been used by traditional healers to cure colds and chest infections for centuries and is now registered by the South African Health Products Regulatory Body. Unfortunately, its popularity has pushed the species to the brink of extinction in the wild as commercial muti gatherers have been harvesting the bark from trees growing in the wild and even in protected conservation areas. As a result the trees have become increasingly scarce and are now considered critically endangered. The harvesting methods used by muti collectors are not sustainable and the trees often die a few months after harvesting.

Thankfully, a collaborative effort between Kruger National Park, Sappi, South African National Biodiversity Institute (SANBI), Agricultural Research Council (ARC), Honorary Rangers and many other partners has brought this species back from the brink. A key part of the initiative is to promote the planting of the tree in suitable areas and to educate traditional healers and muti collectors how to harvest from the trees in a sustainable way that does not kill them off.

The FSA team decided to support this programme by distributing pepper-bark saplings in the small-scale grower communities to celebrate Arbor Week.

Nathi Ndlela putting in the work on a hot spring day in Zululand, where he planted a tree with learners of Amabuye Secondary School.

The event started in Mpembeni, part of the Dube Tribal Authority, where FSA's Business Unit Manager, Nathi Ndlela and small scale grower representative Rejoice Shozi, handed over trees to learners at Amabuye Secondary School and planted a tree with the learners. Trees were also handed over to local traditional leaders and traditional healers.

This was followed by a handover of trees by local small grower representative Busi Mnguni to community leaders, traditional healers as well as learners at Kantayi Secondary School at the iMkhwanazi Tribal Authority area near Port Dunford in Zululand.

Small grower representative Busi Mnguni addresses the Mkhwanazi Tribal Authority, community leaders and traditional healers about the value of conserving and sustainably harvesting the pepper-bark tree.

“Small-scale growers are the ones with the deepest ties to the communities neighbouring South Africa's forestry plantations, so it made sense to go through them when organising an Arbor Day celebration aimed at benefitting forestry communities and conservation," explained FSA’s Nathi Ndlela.

Commented Rejoice Shozi, FSA Small-Scale Grower representative : "I am happy and proud to be creating this connection between FSA and my community, it is important. It is also important that we are doing something that will benefit the conservation of nature and our soil, planting trees does this and we need to do more of it."

"We are highly appreciative of FSA coming into our community and donating these trees,” commented traditional healer Zakhele Nxumalo. “Pepper-bark trees are no longer found in our indigenous forests and people cannot access it locally. With these trees we can change this. We have also learnt today about how to grow and harvest these trees correctly, that cutting the bark can kill the tree, so it is better to harvest just the leaves that also have medicinal properties."

Traditional healer Zakhele Nxumalo (left), had never seen an actual pepper-bark tree before receiving his own sapling from FSA. He has to travel to Durban's muthi market to buy ‘isibhaha’.

Kruger National Park
The initiative to save the pepper-bark tree was launched in 2011 initially to propagate the trees and distribute them to communities living around the Kruger National Park in an attempt to take the pressure off the few remaining wild trees. In 2014, Sappi came on board and began using its tree breeding and production expertise to propagate pepper-bark trees from cuttings for distribution to rural communities, which expanded the project from the Kruger National Park to KwaZulu-Natal and the Eastern Cape.

A major breakthrough for the project was the discovery that the medicinal properties so highly prized in the bark, are also abundant in the twigs and leaves. Thus, the twigs and leaves of trees planted out in the field can be harvested within four years – much earlier than would be the case for bark harvesting which can only be done on an adult tree. This ensures that the trees can be harvested sustainably, providing health benefits and economic opportunities for traditional healers and muti traders alike.

A key aspect of the project is education. Workshops are held with traditional healers and community members to inform them about growing and nurturing the trees, as well as harvesting them sustainably.

A working group has been set up to co-ordinate and drive the Warburgia salutaris conservation project going forward. Gene banks and seed orchards have been established within this working group partnership, and assistance has been extended to Swazi and Zimbabwean conservation authorities to help them increase the number of trees growing in their countries.

Michele Hofmyer who has been involved with the Warburgia programme from the start, explains the importance of pepper-bark distribution programmes: "By handing out the plants freely to traditional healers and community members, we are taking the pressure off the wild populations. Traditional healers know what a rare and valuable plant this is, so are willing to accept cultivated pepper bark if they know the seeds were sourced from wild individuals. They are also open to new ways of utilising the plant, using the newest two leaves and bud instead of the bark, which are just as potent as the bark but far more sustainable to harvest. The robust nature of the pepper-bark tree, its readiness to grow in sunlight or shade and its ability to be planted straight into the ground or in a tub, makes it incredibly suitable to this kind of project. I hope that one day when we drive through the communities and neighbourhoods that have received our trees, there will be a pepper-bark growing in every garden, school and community building.”

Thanks to the efforts of the Warburgia Programme, it looks like the pepper bark's conservation status will be downgraded from ‘endangered’ to ‘vulnerable’ when it is next reviewed.

The tree is formally protected under SA legislation in the revised National Forests Act (2012) and the National Environmental Management Biodiversity Act (2004).

New protected trees in SA

Four new species have been added to the list of trees that are protected under the National Forests Act in South Africa - the Red Ivory, Jackal Berry, Manketti and Umtiza.

The four trees were added to the Protected Trees list by the Minister of Environment, Forestry and Fisheries Barbara Creecy and published in the Government Gazette on 25th March 2022.

The list of Protected Trees includes a broad range of important indigenous trees found in diverse habitats from dense natural forests of the Cape, to woodlands and semi-arid Karoo and Namaqualand. It also includes threatened species such as the Clanwilliam Cedar, the Umtiza and the Pepper Bark tree which has been heavily harvested for muti and is now being propagated and planted out in an effort to increase its numbers in the wild.

In terms of the law anyone who cuts, disturbs, damages, destroys or interferes with any of the 53 protected trees could be convicted and sentenced to three years imprisonment, or fined or both.

"No person may cut, disturb, damage or destroy any protected tree or possess, collect, remove, transport, export, purchase, sell, donate or in any other manner acquire or dispose of any protected tree except under a license granted by the Minister," notes the gazette.

Exceptions to this law are only applicable to those who have been granted a special license or exemption by the Department.

The four new protected trees are:-

Berchemia zeyheri  aka Red Ivory or Rooihout

Red Ivory is an evergreen to semi-deciduous tree. It is drought-resistant but not frost-resistant, and usually grows in dense groups, reaching 15 metres in height. It is evergreen to semi-deciduous and is commonly found in Limpopo, where its fruit is picked and sold on the street.

Wood from the tree is used to make durable furniture, while its leaves and fruit are favoured by birds and bushbuck.

It has yellow-ish sapwood and hard, heavy heartwood. Leaves are blue-green with reddish stalks. Flowers are yellow or green-white and grow in clusters. The fruit is yellow to brown-red.

Red ivory trees occur naturally from Zimbabwe to the Eastern Cape in South Africa, and are common in Limpopo. It grows in woodland, bushveld, rocky areas, along rivers, streams and on old termite mounds. It is also found on south and east-facing mountain slopes.

The fruit of red ivory is delicious and can be eaten fresh or stored in containers, and is sold by hawkers in northern Limpopo. It is also a source of food for many birds and wild animals including baboons, vervet monkeys and bushbabies.

The wood is good for making strong and durable furniture, also wooden bows, walking sticks, small boxes, curios and fencing poles. In KwaZulu-Natal it was known as the ‘royal tree’ because only chiefs were allowed to carry knob-kerries made from Red ivory. The wood is also highly regarded in Mozambique.

Diospyros mespiliformis aka African ebony or Jackal-berry

Jackal-berry trees are found throughout Africa as well as in South Africa, where they are common in savannas or savanna woodlands like the Kruger National Park. It is one of the savanna giants that can live for over 200 years.

This tree has a dense, evergreen canopy and can grow up to 25 metres high, with a trunk circumference of five metres. It can often be found growing on termite mounds, and produces a fleshy oval, yellow-green fruit which is sought after by nyala, impala, warthog, baboons and hornbills.

The tree is widely distributed throughout the eastern part of the African continent, from Ethiopia to the south of Swaziland. It grows well in areas with plenty of water and little or no frost.

The tree is not threatened in South Africa, but because of its important role in the ecosystem and the food web, it is listed as a protected tree.

Many insects such as bees and wasps play a role in pollinating the flowers, while seeds are dispersed either through wash-off by rain or in the droppings of animals that feed on the fruits. Termites often build their nests around the tree and feed on the roots. The tree benefits from moisture and aeration as a result of termites burrowing in the soil beneath it. Snakes are often found around these trees as they prey on the rodents and birds that feed on the fruits.

Fallen fruit is eaten by kudu, impala, nyala and jackal, while the leaves are eaten by elephant, kudu and eland. The larvae of the emperor butterfly also feed on the leaves.

The fruit is popular with local people who eat it fresh or dried. The wood is tough and used to make spoons and canoes, while different parts of the tree are used for muti.

It is a good shade tree and makes an excellent screen or windbreak.

Schinziophyton rautanenii aka False balsa, Manketti tree or Mongongo nut

This tree can be found across Africa in southern Tanzania, southern DRC, Angola, Namibia, Botswana, Zambia, Malawi, Zimbabwe, Mozambique and in Limpopo province in South Africa.

It is a large spreading tree which usually grows to between 15 to 20 metres tall, with grey to pale golden-brown bark. Leaves are dark green above, pale grey below, turning bright yellow before falling.

The light grey-green fruit is covered in velvety hairs, while its hard seeds produce an edible oil.

It grows well on sandy soils in deciduous woodland, along rivers, on wooded hillsides, often on Kalahari sand and sometimes forming large stands.

Cuttings have been used in Angola for live fences and the tree has potential in desert encroachment prevention. A number of cases have been reported where fence posts made from freshly cut posts grew into large trees. The fibrous inner bark is used to make strings for nets and the seeds are used in board games.

The heartwood is straw-coloured and the grain is straight or wavy. The wood is very soft and light, but comparatively strong in relation to its weight, though not very durable. The wood is used for diverse purposes, including floats, canoes, notice boards, boxes, tools, musical instruments and carvings. It can be used as a substitute for balsa wood, hence the common name.

Umtiza listeriana aka Umtiza  

Umtiza is a localised tree, part of the legume family, that is found only in Southern Coastal Forest and Scarp Forest in the East London, Kentani and King William’s Town Districts of the Eastern Cape. This rare evergreen tree grows up to 12 metres in height and produces oblong leaves 20 to 60 mm long. Its dark green foliage make it ideal for small gardens or for use as a shade tree or screen. It is a slow grower, has rough dark brown bark and is covered in thorns.

Umtiza also produces fruit which matures into brown and woody pods.

Rapid human expansion in these areas threatens Umtiza which are becoming increasingly rare. It has been Red Listed as a Vulnerable Species. Umtiza trees are being restored in the Umtiza Nature Reserve near East London where it is reported to be doing well.

Umtiza has hard, oily wood and has been used to make propellor shafts for small boats. It is revered by Xhosa people who use it to ward off lightning and evil spirits.

For more info on these and other protected trees, visit

Below is a full list of the Protected Trees in South Africa.

Afrikaans (A), Northern Sotho (NS), Southern Sotho (S), Tswana (T), Venda (V), Xhosa (X), Zulu (Z)
Acacia eriolobaCamelthornKameeldoring(A), Mogohlo (NS)
Acacia haematoxylonGrey camel thornVaalkameeldoring (A) / Mokholo (T)
Adansonia digitataBaobabKremetart (A), Seboi (NS), Mowana (T)
Afzelia quanzensisPod mahoganyPeulmahonie (A), Mutokota (V), Inkehli (Z)
Balanites subsp. maughamiiTorchwoodGroendoring (A), Ugobandlovu (Z)
Barringtonia racemosaPowder-puff treePoeierkwasboom (A), Iboqo (Z)
Berchemia zeyheriRed IvoryRooihout (A), Munia-niane (V)
Boscia albitruncaShepherd’s treeWitgat (A), Mohlôpi (NS), Motlhôpi (T), Muvhombwe (V), Umgqomogqomo (X), Umvithi (Z)
Brachystegia spiciformisMsasaMsasa (A)
Breonadia salicinaMatumiMingerhout (A), Mohlomê (S), Mutulume (V), Umfomfo (Z)
Bruguiera gymnorrhizaBlack mangroveSwart-wortelboom (A), Isikhangati (X), Isihlobane (Z)
Cassipourea swaziensisSwazi onionwoodSwazi-uiehout (A)
Catha edulisBushman’s teaBoesmanstee (A), Mohlatse (NS), Igqwaka (X), Umhlwazi (Z)
Ceriops tagalIndian mangroveIndiese wortelboom (A), Isinkaha (Z)
Cleistanthus schlechteri var. schlechteriFalse tambotiVals-tambotie (A), Umzithi (Z)
Colubrina nicholsoniiPondo weeping thornPondo-treurdoring (A)
Combretum imberbeLeadwoodHardekool (A), Mohwelere-tšhipi (NS), Motswiri (T), Impondondlovu (Z)
Curtisia dentataAssegaiAssegaai (A), Umgxina (X), Umagunda (Z)
Diospyros mespiliformisAfrican ebony, jackal-berryJakkalsbessie (A), Musuma (V), Mgula (Tsonga)
Elaeodendron transvaalensisBushveld saffronBosveld-saffraan (A), Monomane (T), Ingwavuma (Z)
Erythrophysa transvaalensisBushveld red balloonBosveld-rooiklapperbos (A), Mofalatsane (T)
Euclea pseudebenusEbony guarriEbbehout-ghwarrie (A
Ficus trichopodaSwamp figMoerasvy (A), Umvubu (Z)
Leucadendron argenteumSilver treeSilwerboom (A)
Lumnitzera racemosa var. racemosaTonga mangroveTonga-wortelboom (A), Isikhaha-esibomvu (Z)
Lydenburgia abottiiPondo bushman’s teaPondo-boesmanstee (A)
Lydenburgia cassinoidesSekhukhuni bushman’s teaSekhukhuni-boesmanstee (A)
Mimusops caffraCoastal red milkwoodKusrooimelkhout (A), Umthunzi (X), Umkhakhayi (Z )
Newtonia hildebrandtii var. hildebrandtiiLebombo wattleLebombo-wattel (A), Umfomothi (Z)
Ocotea bullataStinkwoodStinkhout (A), Umhlungulu (X), Umnukane (Z)
Ozoroa namaquensisGariep resin treeGariep-harpuisboom (A)
Philenoptera violaceaApple-leafAppelblaar (A), Mphata (NS), Mohata (T), Isihomohomo (Z)
Pittosporum viridiflorumCheesewoodKasuur (A), Kgalagangwe (NS), Umkhwenkwe (X), Umfusamvu (Z)
Podocarpus elongatusBreede River yellowwoodBreederivier-geelhout (A)
Podocarpus falcatusOuteniqua yellowwoodOutniekwa-geelhout (A), Mogôbagôba (NS), Umkhoba (X), Umsonti (Z)
Podocarpus henkeliiHenkel’s yellowwoodHenkel-se-geelhout (A), Umsonti (X), Umsonti (Z)
Podocarpus latifoliusReal yellowwoodOpregte-geelhout (A), Mogôbagôba (NS), Umcheya (X), Umkhoba (Z)
Protea comptoniiSaddleback sugarbush
Protea curvataSerpentine sugarbushSerpentynsuikerbos (A)
Prunus africanaRed stinkwoodRooi-stinkhout (A), Umkhakhase (X), Umdumezulu (Z)
Pterocarpus angolensisWild teak KiaatKiaat (A), Morôtô (NS), Mokwa (T), Mutondo (V), Umvangazi (Z)
Rhizophora mucronataRed mangroveRooi-wortelboom (A), Isikhangathi (X), Umhlume (Z)
Schinziophyton rautaneniiManketti tree/Mongongo nut
Sclerocarya birrea subsp. caffraMarulaMaroela (A), Morula (NS), Morula (T), Umganu (Z)
Securidaca longependunculataViolet treeKrinkhout (A), Mmaba (T)
Sideroxylon inerme subsp. inermeWhite milkwoodWit-melkhout (A), Ximafana (X), Umakhwelafingqane (Z)
Tephrosia pondoensisPondo poison peaPondo-gifertjie (A)
Umtiza listerianaUmtiza
Warburgia salutarisPepper-bark treePeperbasboom (A), Molaka (NS), Mulanga (V), Isibaha (Z)
Widdringtonia cedarbergensisClanwilliam cedarClanwilliam-seder (A)
Widdringtonia schwarziiWillowmore cedarBaviaanskloof-seder (A)

KZN forest needs your help

A local artist and environmental NPO are rallying efforts to conserve a rare and shrinking patch of indigenous mistbelt forest on the northern edge of Pietermaritzburg, KwaZulu-Natal, which is under threat from alien plant invasion.

Ferncliffe is the precious remnant of a biome that originally stretched over 2 000 hectares. This magical tangle of vegetation, situated right at the edge of the city’s urban sprawl, is blessed with high rainfall and is often swathed in mist.

Although Ferncliffe is small, it still contains an astonishing diversity of life, ranging from large mammals like bushpig and caracal, to unusual millipedes and amphibians, a species of carnivorous snail, and the enormous monkey-catching crowned eagle. It harbours unexpected, often secretive creatures that dwell in, and depend upon, the profusion of indigenous plants that grow there.

Unfortunately, a tide of alien plants is threatening the ecosystem's survival. This environmental degradation is an enormous problem. Now members of the public are invited to assist efforts to restore the biodiversity of this mist-drenched wonder.

To help fund the registered NPO’s vital work, local fine artist Connor Cullinan is producing a series of original art prints that are sold online as open editions via Since 1991, Cullinan has participated in several solo and group exhibitions at a number of respected galleries - these include Obert Contemporary, Erdman Contemporary, Barnard, whatiftheworld and Daor Contemporary. His screenprints have been shown at the FNB Joburg Art Fair, Cape Town Art Fair and Turbine Art Fair. Outside of South Africa, he has showcased his work in Queretaro and Oaxaca in Mexico; his paintings and prints form part of the Nando's permanent collection and are on show in various countries; and his work is held in private collections in Europe and the United States.

His beautifully illustrated images in aid of Ferncliffe are based on the fauna and flora that can be found in the forest and on its fringes. The first two prints in this ongoing series have already been released and were produced at Black River Studio in Cape Town. They depict a tenderly hand-drawn porcupine and the vibrantly yellow Forest Weaver. These art prints make a meaningful acquisition, whether for a formal art collection or to grace the walls of your home.

There are other ways of participating in the restoration of Ferncliff too. You can adopt an existing tree, plant a tree (which comes with an exquisite tree certificate appointing you as an honorary forester), make a straightforward donation, or contribute to unemployment alleviation by sponsoring a day’s wage to clear invasive aliens. Whether it’s for conscious corporate gifting, or a thoughtful gesture for a friend or loved one, you’ll be reaffirming how much the world needs forests, and how much these forests need us…

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