Earth Overshoot Day: Climate Crisis Impacts on South Africa’s Plant Diversity

Written by Zoë Chapman Poulsen. Photos by Nigel Forshaw, Zoë Chapman Poulsen & Isobel Johnson.

Earth Overshoot Day: A Critical Threshold for the Planet

Above: The agricultural landscape of the Overberg looking towards Caledon at the height of the 2017 drought. Photo: Zoë Chapman Poulsen.

This year’s Earth Overshoot Day falls on 22 August of this year, acting as a reminder to all of our impact on the planet. Earth Overshoot Day is the day of the year that we cross an important threshold, the date that humanity’s demand for ecological resources exceeds that which the Earth can regenerate during that year.

With 60% of humanity’s ecological footprint being carbon, there is no hiding from the climate crisis, which is already impacting on the ecosystems and biodiversity of southern Africa. This week on the BotSoc Blog we will be taking a closer look at how the changing climate is impacting and may continue to impact on South Africa’s ecosystems and plant diversity.

The Climate Crisis: Increasing Temperatures & Aridity for southern Africa

Above: In 2017 the Calvinia Dam sits empty after two years of no rainfall during the worst drought in living memory. Photo: Zoë Chapman Poulsen.

South Africa is one of Africa’s leaders in climate change research, and the findings are deeply worrying. Climate change plays a significant role in impacting on water resources, food and water security, health and ecosystem services. Recognition of the problem and finding solutions for climate change mitigation and adaptation are key.

South Africa’s average annual temperatures have increased by at least 1.5 times more than the global average over the last 50 years. These trends are forecast to continue with temperatures projected to rise by 3-6°C by 2081-2100. Models also suggest that most parts of South Africa are likely to become drier, with increasing frequency of extreme rainfall events already a reality.

On the Red List of South African Plants, a relatively small number of species have been identified as being at risk due to climate change, but this number is likely to increase as our understanding of how plants respond to the climate crisis improves.

On the Edge: Impacts of Drought

Above: Drought has lead to extensive mortality of shrubs in the Succulent Karoo near Louriesfontein, Namaqualand. Photo: Zoë Chapman Poulsen.

Increasing aridity and temperatures due to climate change have been forecast to lead to greater frequency and intensity of drought periods, particularly affecting semi-arid ecosystems in South Africa including the Nama Karoo and Succulent Karoo.

With these ecosystems normally reliant on low but stable winter rainfall to trigger growth of plants including both autumn and winter flowering geophytes (bulbs), extreme drought and increasingly unreliable rainfall are becoming commonplace. In Namaqualand in response to the current drought, researchers have noted extensive mortality of trees, shrubs and large succulents at a scale never seen before. 

Nowhere to Go: Impacts on Montane Flora

Above: Protea cryophila. Photo: Nigel Forshaw. http://www.inaturalist.org.

South Africa’s mountain ranges including the Cape Fold Mountains, Drakensberg and others are home to a range of specialist species adapted to very specific growing conditions in narrow microhabitats. These makes many of these species more vulnerable to a changing climate as migration to higher altitudes will lead to contraction of their distribution ranges.

It is possible that this may eventually lead to species extinctions when no more suitable habitat can be colonised by growing at increased altitudes. Furthermore, it has been shown that areas at higher elevation have a higher rate of warming. Several members of the genus Protea have been identified as being under threat due to the impacts of climate change on montane species, including Protea cryophila, Protea convexa and Protea montana.

Fiery Futures: Impacts of Changing Fire Regimes

 

Above: Protea seed cone after the Betty’s Bay fire in 2019. Photo: Zoë Chapman Poulsen.

Climate change projections also indicate that in fire prone and fire dependent ecosystems in South Africa such as fynbos, renosterveld, savanna and grassland vegetation types, fire regimes are likely to change to higher fire frequency and intensity. These ecosystems are dependent on fire for their survival, including for the reproduction of many different plant species.

However, if fire frequency increases too much, it is possible that it may move beyond a threshold at which the ecosystem has the capacity to recover post fire. Prolonged post fire drought in the first year after fire has been shown to significantly reduce survival of seedlings, particularly forbs and graminoids. Increasing fire frequencies have also been shown to likely impact on woody species such as members of the Proteaceae family, that require several years between fires to mature, flower and set seed before the next fire moves through the landscape.

Trees on the Move: Climate Change Driving Bush Encroachment

Above: Sub escarpment grassland with forest. It is possible that South Africa’s grasslands may be threatened by bush encroachment with increasing levels of CO₂ due to the climate crisis. Photo: Isobel Johnson.

Increasing levels of atmospheric CO₂ are thought to be associated with bush encroachment and increasing cover of woody vegetation, particularly in South Africa’s savanna ecosystems. These changes have been documented through the use of historical ground-based and aerial repeat photography, supported by findings from chamber based CO₂ level simulation that showed increased vigour and growth of trees in response to increasing CO₂ levels.

It is also possible that these changes may threaten other ecosystems in South Africa such as grasslands with being colonised by woody vegetation. Bush encroachment is likely to have a significant impact on ecosystem services such as grazing and game viewing as part of the tourism industry. Our savannas and other ecosystems may change beyond recognition in years to come.

Further Reading

Bentley, L.K. Robertson, M.P. Barker, N.P. (2019) ‘Range contraction to a higher elevation: The likely future of the montane vegetation in South Africa and Lesotho’, Biodiversity & Conservation (Volume 28): pp. 131-153.

Helme, N. Schmiedel, U. (2020) ‘Namaqualand Nightmare’, Veld & Flora, Issue 106: pp. 14-19.

Slingsby, J.A. Merow, C. Aiello-Lammens, M. Allsop, N. Hall, A.S. Mollmann, H.K. Turner, R. Wilson, A.M. Silander, J.A. (2017) ‘Intensifying postfire weather and biological invasion drive species loss in a Mediterranean type biodiversity hotspot’, PNAS, pp. 1-6 https://doi.org/10.1073/pnas.1619014114

Forests of South Africa

Written by Zoë Chapman Poulsen. Photos by Eugene Moll, Francois du Randt and Zoë Chapman Poulsen.

Introduction

Above: Sand Forest in the False Bay section of iSimangaliso Wetland Park, KwaZulu-Natal. Photo: Francois du Randt.

As the climate crisis has escalated, an increasing global focus has been placed on forests due to their potential for climate change mitigation through carbon storage. Some researchers advocate widespread global tree planting as a solution, despite many of the world’s ecosystems not being tree dominated. There has been a long held and misconstrued idea that we need to plant more trees in South Africa to ‘save the earth’, with forest mistakenly perceived as one of our most threatened ecosystems.

Despite this strong international focus, research and conservation planning around South Africa’s forests have been highly neglected, with the country having few dedicated forest ecologists. Few realise that South Africa’s forests are some of the most species rich temperate forests worldwide. However, indigenous forest only covers 0.56% of South Africa’s landmass. Within South Africa’s extraordinary range of ecosystems, only a tiny proportion of the country provides the necessary ecological conditions to support indigenous forest.

Forest Biodiversity & Biogeography

Above: Northern Afrotemperate Forest in Royal Natal National Park, KwaZulu-Natal. Photo: Zoë Chapman Poulsen.

South Africa’s forests have a highly fragmented distribution, extending in an archipelago of patches from the south-west to the north-east. Forest species richness and diversity increases in a gradient from the southwest to the northeast. Forest extends inland to the Great Escarpment and northwards to Oorlogskloof, Nieuwoudtville. The most extensive forests are found around Knysna and Tsitsikamma.

Variation in climate, topography, altitude and latitude have resulted in a diversity of forest types. The vegetation map of South Africa, Lesotho and eSwatini recognises 12 forest groups divided into 26 forest types. Forest patch size varies with some as small as 1 ha. Research has shown that these smaller forest patches still support the full suite of ecological processes necessary for ecological integrity and are equally important in conservation planning and practice.

Forests and Fire

Above: Southern Afrotemperate Forest in Orange Kloof, Table Mountain after fire. Photo: Zoë Chapman Poulsen.

Within the fynbos and grassland biomes, one of the key determinants of forest distribution is the presence, absence and frequency of fire. Forest is often found growing in natural fire refugia such as in steep sided kloofs, boulder screes or deeply weathered rock cracks. Forest will rarely burn, only with exceptionally high temperatures and windspeeds or drought. Hot and more frequent fires will lead to a forest patch decreasing in size, whereas infrequent fires or long term absence of fire will lead to the forest patch growing in size. This can lead to significant changes in forest distribution over relatively short time scales.

Conservation status and threats facing South Africa’s forests

Above: Tall Sand Forest in Tembe Elephant Park, KwaZulu-Natal. Photo: Francois Du Randt.

Most of South Africa’s forests are currently managed as conservation areas, with a government mandate in place to protect all forests on private, communal and state-owned land in line with the National Forest Act (Act No 84 of 1998). The 2018 National Biodiversity Assessment recognises South Africa’s forests as one of several ecosystem types that provide disproportionate benefits to people relative to their size, including water purification, nutrient cycling, carbon storage, storm protection, recreation and food.

However, some of South Africa’s forests are impacted by wood harvesting for fuel and building materials as well as extensive bark harvesting from certain species for medicinal use. This can lead to eventual death of the tree if the tree is fully ring barked. South Africa’s mangrove forests are classed as Critically Endangered due to habitat loss from harbour development. Riparian gallery forests in Mpumalanga are also threatened due to water abstraction.

Afrotemperate Forest

Above: Afrocarpus falcatus in Southern Afrotemperate Forest in Nature’s Valley, Garden Route. Photo: Zoë Chapman Poulsen.

Afrotemperate forest has two vegetation units: Southern Afrotemperate Forest and Northern Afrotemperate Forest. Southern Afrotemperate Forest is distributed from the Cape Peninsula eastwards to the Eastern Cape, with the main centre of diversity being the Knysna-Tsitsikamma region. This forest type is usually tall and multi-layered and is dominated by yellowwoods (Afrocarpus falcatus and Podocarpus latifolius). Cunonia capensis is present in deep gorge habitats. Northern Afrotemperate Forest is distributed from the Free State and Lesotho northwards to Limpopo, where it is found in small patches in kloofs at higher altitudes. Taller trees present include Celtis africana and Halleria lucida.

Coastal Forest

Above: Coastal dune forest at Twinstreams, Umtunzini, KwaZulu-Natal with an understorey of Isoglossa woodii. Photo: Eugene Moll.

Coastal forest comprises Southern Coastal Forest and Northern Coastal Forest. Southern Coastal Forest is found in the Western and Eastern Cape, including coastal dune systems. These forests are dominated by Milkwood (Sideroxylon inerme) from Llandudno on the Cape Peninsula eastwards to Nature’s Valley. Further east the species richness increases with dominants including Brachylaena discolor and Euclea natalensis. Northern Coastal Forest is found predominantly along the coastline of KwaZulu-Natal and is relatively species rich. It mostly grows on coastal plains and stabilised coastal dunes.

Mistbelt Forest

Above: Mistbelt forest with near endemic Podocarpus henkelii in KwaZulu-Natal. Photo: Eugene Moll.

Mistbelt forests are relatively species rich afrotemperate forests that differ through the presence of subtropical floral elements. Southern Mistbelt Forest is found in the Eastern Cape and KwaZulu-Natal, in fire shadow habitats on south and southeast facing slopes at higher altitudes. Podocarpus henkelii is a near endemic to this vegetation type. The vegetation is dominated by a range of deciduous and semi-deciduous trees such as Celtis africana and Calodendrum capense. Northern Mistbelt Forest is found in Limpopo and Mpumalanga in east facing fire refugia such as moist and sheltered kloofs. There are a number of endemic taxa including Cryptocarya transvaalensis.

Scarp Forest

Above: Scarp forest in the gorge of the Umtamvuna River, KwaZulu-Natal. Photo: Eugene Moll.

Scarp forest is species rich and structurally diverse with a significant number of endemic taxa. It is found in the Eastern Cape, KwaZulu-Natal, Mpumalanga and eSwatini, either on coastal platforms or in deep gorges. This vegetation type was once home to the extinct in the wild Encephalartos woodii, today known only from a few individuals housed in botanical gardens.

Sand Forest

Above: Allelopathic borders in Sand Forest in Tembe Elephant Park, KwaZulu-Natal. Photo: Francois du Randt.

Sand forest is found from KwaZulu-Natal northwards into Mozambique, predominantly in Maputaland. This forest type has a tall forest canopy layer with a relatively depauperate ground layer. Much of this forest has been cleared historically for subsistence agriculture and grazing. Uncontrolled extraction of wood for fuel is also a significant problem. Sand Forest is therefore Critically Endangered.

Mangrove Forest & Swamp Forest

Above: Swamp forest with Barringtonia racemosa flooded at Twinstreams, Umtuzini, KwaZulu-Natal. Photo: Eugene Moll.

Mangrove forest and swamp forest are both azonal vegetation units. Swamp forest is found at low altitudes in KwaZulu-Natal and the Eastern Cape on muddy waterlogged soils. The tree Raphia australis is endemic to this vegetation. Mangrove forests are found in coastal estuaries in the Eastern Cape and KwaZulu-Natal, making them the highest latitude coastal mangroves in the world. This vegetation is Critically Endangered due to historic habitat loss from harbour development.

Further Reading

du Randt, F. (2018) The Sand Forest of Maputaland, South African National Biodiversity Institute, Pretoria, South Africa.

Mucina, L. Geldenhuys, C.J. (2016) ‘Afrotemperate, subtropical and azonal forests’, pp. 585-615 in Mucina, L. Rutherford, M.C. (Eds) The Vegetation of South Africa, Lesotho and Swaziland, Strelitzia 19, South African National Biodiversity Institute, Pretoria.

Venter, E. (2011) Trees of the Garden Route: Mossel Bay to Storms River, Tien Wah Press, Singapore.

Von Breitenbach, F. (1974) Southern Cape Forests and Trees, The Government Printer, Pretoria, South Africa.

KZN Coastal Branch: The secret life of mangroves

Written by Sandra Dell & Zoë Poulsen. Photos by Tony Dickson

Above: The group gathers at the Beachwood Mangroves Nature Reserve lapa.

On Saturday 3 August the  BotSoc KZN Coastal Branch visited Ezemvelo KZN Wildlife’s Beachwood Mangroves Nature Reserve on a guided walk to learn more about this extraordinary ecosystem. The visit was led by aquatic scientists Professor Ticky Forbes and Nicolette Forbes from consultancy Marine and Estuarine Research (MER). The group was also kindly accompanied by the Beachwood Honorary Officers. The reserve’s lapa and parking area will be the same venue for the BotSoc branch’s indigenous plant fair to be held on 7 & 8 September.

Above: Nicky Forbes reveals the wonders of the intertidal zone and the mangroves that are adapted to thrive there.

Beachwood Mangroves Nature Reserve is one of Durban’s hidden gems. The reserve is normally closed to the public except by appointment but opens on the third Saturday morning of each month for guided walks led by the Honorary Officers. A boardwalk trail through the reserve allows easy access for visitors. Located at the Umgeni River mouth in Durban North, it is one of the last protected fragments of mangrove habitat on the KZN coastline. Mangrove forest is classed as ‘Critically Endangered’, with much of its original extent lost as a result of harbour development, urban development and degradation through unfavourable agricultural practices inland.

Above: A Grey Heron arrived and we eyed each other out.

Mangrove forest is found along South Africa’s eastern coastline where it is warmed by the Mozambique current from Kosi Bay southwards to Nahoon Estuary. This ecosystem forms between mean sea level and mean high water spring tide level in sheltered estuaries on tidal flats. The soils on which they grow are saline and fine grained with poor drainage and high organic content. Mangroves protect the shoreline against extreme weather, stabilise the shoreline and provide a vital habitat for their fascinating flora and wildlife.

Above: The Beachwood Honorary Officers kindly accompanied us. They lead walks during a monthly open day on the 3rd Saturday morning of each month.

There are three different mangrove species present in the Umgeni estuary, each one with its own unique adaptations for eliminating salt. As the scientific name suggests, the Red Mangrove (Rhizophora mucronata) has a ‘mucro’ or needle-like point on the leaf tip. The roots are extensive prop roots of up to 30 metres that anchor and stabilise the tree despite its relatively diminutive height. Red Mangrove Crabs feed on the leaves of this species, collecting the dropped leaves and taking them down their burrows for food.

Above: Red Mangrove Crab collecting fallen leaves for food.

The Black Mangrove (Bruguiera gymnorrhiza) has stabilising buttress roots and underground cable roots. The cable roots loop upwards to form knee roots for taking in oxygen. Nutritive roots also lead from the cable roots into the mud. The White Mangrove (Avicennia marina) is a primary coloniser that allows the other two mangrove species that are found here to grow. Its root system is extensive and consists of shallow, horizontal cable roots with pencil roots (also known as pneumatophores) growing upwards and above ground in fine sediment and when the ground is waterlogged, allowing the tree to breathe.

Above: Here erosion has exposed more of a Black Mangrove’s root system than we might normally see.

Another plant that was seen was the Matting Rush (Juncus kraussii). This plant is in demand in the wild for material used for making sleeping mats. The group also stopped to observe the antics of male Fiddler Crabs with their comical enlarged single orange claws. They may be either left or right ‘handed’, waving their claws to attract females. Different species have different waving patterns.

Above: Matting Rush (Juncus kraussii).

After arriving back at the lapa, Nicolette Forbes showed the group some historical aerial photographs of the reserve. Interestingly these showed that the site now has far more mangroves present than there were in the 1930s. Four dams that have since been built have meant that there are no longer strong river flows, thus allowing more shallow sandbanks to form and hence mangroves to grow.

Above: Male Fiddler Crab.

The KZN Coastal Branch would like to thank Ticky and Nicolette Forbes for a wonderful outing. The Forbes gave patient explanations on many complex subjects around mangrove ecosystems. For more information, please see their recent update of the WESSA handbook, ‘In the Mangroves of Southern Africa’. Thank you too to the reserve’s Conservation Manager Basil Pather, the Ezemvelo KZN Wildlife staff and Honorary Officers for all of their assistance.

Paintbrushes of the Veld: Spotlight on Haemanthus

Article and photos by Zoë Poulsen

Known for its bizarre paintbrush-like flowers, the genus Haemanthus is one of the most famous of the Amaryllidaceae family. When autumn comes to the veld and little else is in flower, these strange blooms emerge from the dry earth where they have been lying dormant over the summer months. The genus is endemic to Southern Africa and found only in Namibia, South Africa, Lesotho and Swaziland with the main centres of diversity being central and southern Namaqualand and the Knersvlakte around Vanrhynsdorp. Some species are widespread and occur across a wide variety of different habitats whereas others are specialists adapted to a specific habitat niche. Some Haemanthus from winter rainfall areas flower in profusion after fire has cleared overstorey vegetation. Most members of the genus grow in colonies, a phenomenon perpetuated by the peduncles leaning towards the ground under the weight of the seeds as they ripen leading to germination around the parent plant.

Above: Haemanthus albiflos growing in afrotemperate forest habitat on the Garden Route.

Haemanthus albiflos is one of only three evergreen species of Haemanthus. It was first described and illustrated by N.J. Jacquin in 1797 from material collected from the Cape. This species is distributed from Stilbaai eastwards to northern KwaZulu Natal where it grows in coastal and riverine forest, thornveld and valley bushveld in light to deep shade. Flowering takes place from May to October.

Top & Above: Haemanthus coccineus in flower and fruit on the Bokkeveld Escarpment.

Haemanthus coccineus is the most widely distributed members of the species. It is found from southern Namibia southwards to the Cape Peninsula, eastwards to the southern Eastern Cape and inland to Sutherland and Ladismith. This species is found in habitat as varied as its distribution, growing on soils derived from sandstone, granite, quartzite, shale and limestone. Haemanthus coccineus is often found in rocky habitats where it commonly grows in the shade of boulders. In contrast it is also found growing on coastal dunes. Flowering occurs from February to April.

Above: Haemanthus barkerae flowering in habitat.

My first encounter with the intense pink inflorescences of Haemanthus barkerae was a lonely flowerhead lying on the ground after having likely been removed by foraging baboons. This species is endemic to South Africa’s Northern Cape, distributed from Louriesfontein to the Hantamsberg and northern Tanqua Karoo where it grows on heavy clay soil. Haemanthus barkerae was only recently described, previously being thought to be part of Haemanthus pumilio until it was revised by Dee Snijman in 1984. Flowering takes place from March to April.

Above: Haemanthus canaliculatus flowering after fire in Hangklip Sand Fynbos.

Haemanthus canaliculatus is another range restricted member of the genus, known only from the Overstrand coast between Rooiels and Betty’s Bay. It was first collected in Betty’s Bay by a Mrs. M Brunt in 1943, but not described until 1966 by botanist Margaret Levyns in the Journal of South African Botany. The species epithet of Haemanthus canaliculatus refers to the deeply channelled leaves that typify this species. It is a wetland specialist, growing in peat in Hangklip Sand Fynbos. It flowers in profusion after fire, growing in dense colonies. Haemanthus canaliculatus is Endangered on the Red List of South African Plants as a result of housing development reducing the number of populations.

Above: Endangered Haemanthus pumilio flowering in habitat.

Last but not least is the diminutive Haemanthus pumilio, its species epithet meaning ‘dwarf’ in reference to its low growing habit. This species was first described in 1797 by N.J Jacquin having been introduced to RBG Kew by Francis Masson who collected it at an unrecorded locality at the Cape. Haemanthus pumilio is endemic to the lowlands around Stellenbosch and Paarl where it grows on gravelly clay flats in renosterveld vegetation. Much of its habitat has been lost as a result of urbanisation and transformation for agriculture and it is now only known from a handful of sites. Flowering takes place from March to April and the seeds are thought to be water dispersed. Haemanthus pumilio is listed as Endangered on the Red List of South African Plants.