Search for biocontrol of invasive American bramble intensifies

Rubus section Arguti plant, Cedara. Photo: Costas Zachariades

Invasive American bramble is a thorn in the side of foresters, farmers and land managers across large swaths of South Africa. It chokes up grasslands, forest fringes and river banks, and is notoriously difficult to eradicate. But there is light at the end of the tunnel as a team of scientists are tracking these elusive invaders to find an effective biological control …

American bramble continues to be a major scourge to agriculture, forestry and biodiversity conservation in many of the temperate areas of KwaZulu-Natal, Mpumalanga and Limpopo provinces. The weed forms impenetrable, thorny thickets which impede the passage and access to water of livestock and other animals, replace grazing, smother young plantation trees and make the maintenance and harvesting of older trees difficult. Bramble infestations replace native vegetation, with negative consequences for natural ecosystems, particularly in temperate grasslands. They can also negatively affect specialist flower-visitors. Native bird species increase the spread and germination rates of invasive alien brambles.

There are a number of indigenous bramble species in South Africa, as well as several invasive alien ones. These all belong to the genus Rubus, which falls under the rose family Rosaceae. There are also many species, hybrids and varieties of cultivated Rubus. The most well know of these are the blackberries and raspberries, but they also include youngberries, boysenberries, cloudberries, dewberries and loganberries. There is a small berry industry in South Africa, but most of that sold in our shops is imported – Mexico, for example, is currently one of the main exporters of blackberries worldwide.

Examples of fruits on Rubus section Arguti, southern KZN. Photo: Grant Martin.

The biology of Rubus is somewhat unique, in that most or all species, although perennial, have a biennial flowering and fruiting cycle. “Primocanes” grow from the ground in the first year – long, robust stems which bear no flowers or fruit. In the second year, these become “floricanes”, which bear the flowers and fruit, and subsequently die back. The study of Rubus is also quite specialized, and comes with its own moniker – “batology” – while those who work with Rubus are known as batologists!

The genus Rubus is large and complex, and is characterized by its ability to hybridise. The genus is divided into a number of Subgenera, and within each of these, one or more ‘Sections’. It is widely distributed, with native representatives on six continents, and invasive alien species and hybrids are also widely distributed and cause great harm in certain areas. In South Africa, American bramble is the most damaging of the invasive brambles. Several introductions of various brambles into South Africa were made in the late 19th and early 20th century, chiefly with berry production in mind. By the 1930s, however, American bramble was becoming problematic: an early reference to this bramble as “Rubus cuneifolius” was by E.J. Philips and co-authors in 1939, in “Farming in South Africa”. Rubus cuneifolius is native to Florida and the southern states of the USA, with the common name “sand blackberry”. However, it was soon realized that there was more than one form of this bramble; J.P. Marais, in a 1960 report, divided it into the “Hilton Road variety” (which was shorter, more upright, and grew in more open areas) and the “Richmond variety” (taller, with more arching canes, growing more prominently in more sheltered areas with partial shade).

Jacobus Egberink carried out some of the first comprehensive studies on the weed and its control as part of his MSc in Agriculture through the University of Natal (now UKZN), completed in 1965. Dr Danie Erasmus, based at the Cedara campus of the Plant Protection Research Institute of the national Department of Agriculture (now the Agricultural Research Council’s Plant Health and Protection [ARC-PHP] institute) conducted further work in the 1980s, including on chemical control. Various other studies, on the biology and taxonomy of Rubus in South Africa, were also undertaken in the 1980s by Prof. Charles Stirton, Dr Johan Spies and Henriette du Plessis.

Rubus section Cuneifolii invasion in the Drakensberg. Photo: Michal Sochor.

Worldwide, biological control of Rubus species initially achieved low success, mainly because of the complex nature of the genus, in particular its tendency to hybridise, and therefore difficulties in finding natural enemies in the region of origin that were able to develop on the introduced target weeds. With the advent of genetic techniques, success rates have increased. In South Africa, the first attempts towards Rubus biocontrol were undertaken by Dr Mike Morris and colleagues of the Agricultural Research Council’s Plant Protection Research Institute in the 1990s, using plant pathogens (rust fungi). They discovered that one of these (Kuehneola uredines), already widespread in the country, only developed on the upright form of R. cuneifolius, and was not particularly damaging. They then imported another rust fungus (Gymnoconia nitens) from Florida, USA, where it had been collected off R. cuneifolius, into their quarantine laboratory. However, this fungus only infected some specimens of the sprawling form of American bramble, as well as a commercial variety of Rubus and a native species, so it was rejected as a biocontrol agent. Because of the differences in infection patterns between upright and sprawling forms of R. cuneifolius, Dr Morris and his team believed that these might in fact be two separate species; they also realized that the upright form tended to grow at higher altitude than the sprawling form. In the early 2000s, ARC-PHP attempted to initiate genetic work in order to understand origins and identities of the forms of American bramble present in South Africa, in collaboration with Dr Lawrence (Larry) Alice of Western Kentucky University, USA, but this project did not come to fruition.

Recent efforts – from 2018 on

Given the ongoing problems caused by American bramble, interest in undertaking a feasibility study revived in 2018. A small ARC-PHP project (managed by Dr Costas Zachariades) was granted funding by the Department of Environmental Affairs (its Natural Resource Management Programmes directorate, which includes the Working for Water programme). At a similar time, the recently formed Centre for Biological Control, attached to Rhodes University, initiated a project on northern temperate weeds, under the management of Dr Grant Martin. These two units collaborated. An M.Econ. student, Brett Mason, undertook a study looking at some of the costs and benefits of Rubus in South Africa. Coincidentally, in 2017 a young dynamic researcher from the Centre of the Region Haná for Biotechnological and Agricultural Research, Olomouc, in the Czech Republic, Dr Michal Sochor, had started a study on the taxonomy and phylogeny of Rubus in South Africa, in collaboration with Dr John Manning of SANBI. Dr Sochor had previously undertaken research on the taxonomy and phylogeny of European brambles, and was thus highly experienced and knowledgeable; the European approach differs dramatically from the current American approach: European researchers tend to recognise many more species than their North American counterparts – while the latter are “lumpers”, the former are “splitters”, and will describe “microspecies”. This divergent approach has not been consistent; for example, from 1941-1945, Dr L.H. Bailey undertook the most recent comprehensive revision of the genus in North America, and recognized hundreds of species, many of which he described himself. In stark contrast, Dr Larry Alice, in a 2015 article, sank the entire Rubus section Arguti, consisting of about 110 species listed in Bailey’s monograph, under one species, R. pensilvanicus. While the assignment of variable forms to separate species or microspecies may be complex and confusing, the lumping of many variable forms under one species is not helpful for the purposes of identification of invasive forms and determination of their origins.

Close-up of Rubus section Arguti plant, Cedara. Photo: Costas Zachariades.

Dr Sochor and colleagues used several techniques in their work, including extensive field and herbarium studies across South Africa, aimed at clarifying Rubus taxonomy in the region with the help of DNA – ploidy estimation and assessment of reproductive mode. They have subsequently published their findings in two scientific papers: the first, in 2018, deals with Rubus in the Cape Floristic Region, while the second, in 2022, examines the entire country, and is thus more relevant for the purposes of American bramble. They found that the upright form of what had been previously referred to as Rubus cuneifolius is a separate species, and in a separate section of the genus, to the sprawling form. Unfortunately they were unable to put species names to these, and refer to them only as Rubus section Cuneifolii (upright) and Rubus section Arguti (sprawling). Rubus section Cuneifolii is found predominantly in KwaZulu-Natal, while Rubus section Arguti is more widespread, occurring predominantly in KZN, Mpumalanga and Limpopo. Furthermore, the Arguti plants could be divided into two commonly occurring forms. Interestingly, both Rubus section Cuneifolii and Rubus section Arguti are “facultatively apomictic” (meaning that they can reproduce asexually) – apparently this indicates that both of these invasive Rubus are in fact hybrids, not true species; in discussion with Dr Sochor, he felt it was likely that such hybridization had occurred in North America, under natural circumstances, prior to the plants being imported into South Africa. Dr Sochor and colleagues also identified two hybrids of which one parent was Arguti and the other was one of two indigenous Rubus species, but did not find any hybrids of Cuneifolii.

Left: Dr Grant Martin. Centre: Rubus section Arguti invading young pine plantation, southern KZN (photo by Grant Martin). Right: Dr Costas Zachariades.

A year prior to the publication of the 2022 paper discussed above, Dr Bram van de Beek, a Dutch theologian who had devoted many years to the study of Rubus in South Africa, published an article focusing on the Cape, although he examined material from across the country, using only taxonomic features (i.e. no ploidy or reproductive methods). Collaborating with Dr Mark Widrlechner, an expert on Rubus taxonomy at the University of Iowa, they identified one of the two sprawling forms (Rubus section Arguti) as Rubus originalis and described the other as a new species, Rubus revealii. For the upright form, they identified a few (“stronger”) plants from KZN as Rubus pascuus but used Rubus probabilis for most plants. Dr Sochor does not feel confident in these identifications; in general we have aligned our work with Dr Sochor rather than Dr van de Beek, but we are also working with Dr Widrlechner in the USA.

In order to familiarize ourselves with the South African Rubus flora (both alien and indigenous), we joined Dr Sochor on one of his fieldtrips to South Africa, in early 2020. Despite our initial confusion as non-botanists, we soon found it quite easy to distinguish between various species based on characteristics such as leaf shape and flower colour. This trip also gave us an opportunity to look for natural enemies present on both alien and indigenous Rubus species. This proved interesting, as we found many more species of insects and pathogens on the indigenous species than the alien ones – although this is expected, it does give an indication that many natural enemies of Rubus are specialized, and secondly that were we to introduce natural enemies from North America onto these alien Rubus plants in South Africa, they have the potential to reduce the invasiveness of these plants.


Comparison of flowers and leaves of Rubus section Cuneifolii (top) and Rubus section Arguti (bottom). Photos: Michal Sochor.

Current work and the way forward

What is the relevance of the recent taxonomic and phylogenetic studies discussed above to our biocontrol project? The lack of much hybridization, together with the weediness of the plants, led us to restrict our focus to invasive North American Rubus i.e. plants previously falling under “Rubus cuneifolius” in South Africa. In order to progress, we need to firstly understand how many species, and how much genetic variability exists in these species in South Africa. We hope that it allows us to find plants growing in the USA which are close matches to at least some of these invasive Rubus, and thereby find potential biocontrol agents (insects, mites and pathogens) which are compatible with the plants. To achieve the first goal, Dr Sochor agreed to undertake genetic analysis of these species – we therefore undertook a fieldtrip across KZN in early 2023 to collect as much genetic material and herbarium specimens as possible (the latter have been lodged in the Bews Herbarium at UKZN, Pietermaritzburg). This fieldtrip confirmed previous observations that the upright form (Rubus section Cuneifolii) occurs more commonly at high altitude (KZN Drakensberg), while the sprawling form (Rubus section Arguti) occurs more commonly at lower altitude (KZN Midlands). Dr Martin also opportunistically collected some specimens in the USA while on a fieldtrip there for other purposes. Dr Sochor has conducted some analysis of our specimens, and has concluded that while the upright form is genetically quite homogeneous and consistent with a single species/hybrid, the sprawling form in KZN consists of three species/microspecies/hybrids (we still need to sample Rubus section Arguti in other provinces). Furthermore, he did not find a close match between the South African and North American specimens sampled, and the North American samples displayed a high level of variability amongst themselves.


Stem girdles caused by insect larvae on two indigenous Rubus species. Photos: Brett Mason.

So the identification of North American plants which are genetically close to ours remains a critical step. One way to do this is to obtain genetic material from Rubus herbarium specimens in the USA which are morphologically similar to our invasive ones. Dr Sochor has found that leaf material from herbarium specimens, even those over 100 years old, can yield good DNA. Dr Widrlechner has agreed to assist in obtaining such material, and also in re-examining Rubus specimens of species said to be similar to ours. Bearing in mind that both Rubus section Cuneifolii and Rubus section Arguti in South Africa are hybrids, we may not find a perfect match among herbarium specimens in the US, but we hope this exercise gives us some direction. If so, we can transfer our attention to the field in the US – to areas where these herbarium specimens were originally collected. Again, it would be extremely helpful if a local taxonomist such as Dr Widrlechner could assist us to identify these plants in the field. From there, there are two options, viz. (i) to survey these plants for natural enemies, and to import such natural enemies into quarantine in South Africa; (ii) a better option would be to plant out South African material among genetically similar plants in the USA on which natural enemies are present, and allow these natural enemies to colonise our South African plants on their own. In this way we will be more likely to obtain potential biocontrol agents which are compatible with our plants, and thus more likely to be successful in the field in South Africa, should they prove to have a sufficiently narrow host range (i.e. do not attack native or commercial Rubus) to be safe for release in South Africa. Whether the US biosecurity authorities would permit us to plant out South African Rubus is uncertain, but we plan to apply for permission to do so.

There is a final spoke in the works, and that is a lack of current funding. Funding from DFFE: NRMP became more erratic in 2018, and dried up completely in 2023, with no prospect of revival in the short term. CBC itself has funded some of the work since then, but its means are limited. Adequate funding would allow the US work described above to be undertaken properly, and, should natural enemies be found there that show promise as biocontrol agents, to import these into South African quarantine in order to conduct host-range testing.

Funding notwithstanding, what seemed in the 1980s and 1990s as an intractable, complex situation is now resolving itself into a more manageable research project, with some light at the end of the tunnel due to improved understanding of Rubus taxonomy and phylogeny. It is not inconceivable that within the next 10 years, an effective biocontrol agent could be released for one or more of the invasive North American brambles in South Africa, resulting in reduced vigour and competitiveness of these plants, and correspondingly, more cost-effective management using non-biocontrol methods.

Plant of Rubus section Cuneifolii. Photo: Michal Sochor.

Authors:-
C. Zachariades, Agricultural Research Council’s Plant Protection Research Institute
G. Martin, Centre for Biological Control

Notes from the field
Roger Poole, Member Services Co-ordinator for NCT and Agro-Chemical Liaison Officer for the Timber Industry Pesticide Working Group (TIPWG), provided some useful notes on the chemical control of American bramble …

Bramble is a tricky one due to it having two stages of growth, these being the older stems one always sees and then there is secondary (new) growth you'll find inside the thicket. Timing is critical. Best months to spray are between February through to April as the plant is building up reserves for winter so absorption of herbicide is the most efficient.

The best herbicide is metsulfuron methyl, it is slow acting and gives the best results. If there are other invasive species within the area of treatment, then one can look at glyphosate or the picloram/fluroxypyr formulation.

Glyphosate is not the best but does work on bramble that has been cut down. Depending on the size of the thickets one can apply it with a high pressure unit (bakkie sakkie) or tractor boom sprayer. Knapsacks only work on bramble that a person can walk through so you’ll have to cut the thicket with either a brush cutter or tractor-mounted slasher.

Aerial application has been done previously but water volumes need to be checked and applied as per label due to the need for penetration to ensure the mixture gets through the thicket and results in a good coverage.

Finding biodiversity in timber plantations

Eucalyptus plantation set back from riparian area, Karkloof.

Finding a balance between wood fibre production while conserving biodiversity and minimising environmental impacts is the big challenge facing the forestry industry all over the world. In South Africa it has a particular significance because almost all timber production comes from planted forests established in the wetter grassland areas located along the escarpment and eastern coastal plains.

These plantations, which occupy some 1% of South Africa’s land area, play a vital role in providing the primary raw material for a wide range of products from paper and packaging to structural timber, veneers, boards, fabric and charcoal, to name but a few. The forestry and forest products industry generates 10.4% of South Africa’s agricultural GDP and 4.5% of manufacturing GDP, creating 105 600 direct jobs and 43 500 indirect jobs in the process.

Crucially, these plantations have made it possible to protect the natural forests in South Africa from over-logging by providing the wood fibre needs of the growing population. Many of the plantations in this country were established by government specifically for this purpose.

But the loss of biodiversity which underpins life on earth and the ecosystem services upon which we depend, is a massive red flag for every country in the world, South Africa included. As populations increase more land is transformed from its natural state, and inevitably, the biodiversity supported by those natural systems is negatively impacted.

Sappi Forests Environmental Manager Hlengiwe Ndlovu (left) leads the way across a grassland conservation area at the top of the Karkloof mountains. It is located on Sappi’s Lebanon plantation, and borders with the indigenous forest in the Karkloof Nature Reserve.

This places a heavy responsibility on land managers to proceed cautiously when biodiversity, ecosystem services and the health of the entire natural environment is at stake.

So how do we continue to provide the wood fibre raw materials that we need from alien tree plantations that have transformed natural grassland, while at the same time conserving biodiversity? This was the focus of a recent visit by key staff members from SA National Biodiversity Institute, Department Forestry, Fisheries & Environment, Forestry South Africa and Paper Manufacturers Association of South Africa, to Sappi’s plantations in the Karkloof in the KZN Midlands.

What followed was a fascinating journey from the comfort of the Karkloof Country Club (and a delicious cappuccino) to a natural grassland in the middle of Lebanon plantation at the top of the rugged Karkloof mountains; to the 160 ha Shafton-Kusane wetland surrounded by forestry, dairy and sugar farms; to the magnificent Karkloof Falls where the Karkloof river plunges 105 meters into a gorge before joining the Umgeni river which provides the primary water resource for several million people downstream.

Sappi Forests Environmental Manager Hlengiwe Ndlovu and Sappi’s former Environmental Manager (now retired) and Chairperson of the Sustainable African Forest Assurance Scheme, Dave Everard, provided fascinating insights into the company’s strategy to achieve this elusive balance.

The Karkloof falls, a popular picnic spot, is at the centre of an impressive network of mountain bike and hiking trails.

Water

The thread that stitched this journey together was the water that trickles out of the springs and seeps at the top of the catchment. It makes its merry way along countless streams, through wetlands, natural forest patches, plantations, grasslands and farms, gathering momentum as it goes before entering the mighty Umgeni River which provides life-giving water for millions of people all the way to the coast. The water’s journey serves to emphasize the connectedness of the landscape, the fact that how we use the land in one place ultimately affects the health of the land everywhere.

Key to understanding Sappi’s - and indeed much of forestry’s approach – was the patchwork nature of the landscape. From the top of the Karkloof mountain we could see that the plantations stretching across the valley below were not contiguous wall-to-wall trees. There were open grassland corridors between the tree patches, along the rivers and around the wetlands and the steep, rocky outcrops. These open areas constitute around one third of the forestry company’s landholding, and are proactively managed for conservation purposes.

The way these open, unplanted areas are connected to each other, to the wetlands, high conservation value areas and natural forest patches in the landscape, plays a crucial role in their effectiveness as biodiversity enablers. If well planned out and managed, timber estates can therefore become ‘green corridors’ that allow the free movement of plants and animals, thereby supporting biodioversity in the landscape.

The group that attended the Biodiversity in Forestry field day arranged by the Paper Manufacturers Association of SA (PAMSA) and Forestry South Africa (FSA) and hosted by Sappi Forests at their Karkloof plantations. Left to right: Dave Everard (Chairperson of the Sustainable African Forest Assurance Scheme), Hlengiwe Ndlovu (Sappi Forests Environmental Manager), Julie Borland (R & D consultant, PAMSA), Alex Marsh (SANBI), Jane Molony (Executive Director, PAMSA), Jennifer Zungu (SANBI), John Scotcher (Environmental consultant, FSA), Tshifiwa Ramatshimbila (Director Woodlands & Indigenous Forests, DFFE) and Trudy Sebelebele (Forest Certification Manager, Sappi).

Grassland

The grassland we visited at the top of the mountain was a kaleidoscope of different grasses, forbs and bulbs thanks to the fact that it has been protected from excessive livestock grazing, and periodically burnt to mimic nature and promote biodiversity. Encroaching alien vegetation has been kept at bay.

Directly below the grassland an indigenous forest blankets the steep slopes of the mountain. This forms part of the 3 275 ha Karkloof Nature Reserve which includes 198 ha of Sappi owned land, land leased out by several other private landowners as well as land purchased by Ezemvelo KZN Wildlife. Although the forest was heavily logged back in the day, it has remained undisturbed for half a century and harbours a huge array of birds and animals, plant and tree species including the magnificent yellowwoods and stinkwoods. It lies within the upper catchments of the uMgeni and uThukela rivers which are of crucial strategic importance in supplying water to millions of downstream users.

Undisturbed grassland conservation area in between Lebanon plantation and the indigenous forest of the Karkloof Nature Reserve.

Wetland

The Shafton-Kusane wetland is situated in the centre of the Karkloof valley, and fulfils a vital function of capturing, storing, filtering and slowing down the water that drains out of the mountains. It covers an area of 160 ha and was ranked as highest priority in terms of broad regional conservation priorities and opportunities for providing key goods and services. Sappi has pulled its trees back to expand and protect the wetland, and does on-going invasive alien weed control. They’re also busy upgrading all the stream crossings above the wetland to ensure the water flows freely and unimpeded.

The Karkloof river meanders through the 160 ha Shafton-Kusane wetland before plunging over the Karkloof falls.

Karkloof trails

Below the wetland the river enters forest land again, and then plunges over the spectacular Karkloof waterfall. Here we encounter a different side of forestry. This is the focal point of one of the country’s best known trail networks. There are 250 kms of carefully curated single track trails and forestry roads snaking through plantations, grassland corridors and conservation areas, used by mountain bikers, runners and hikers from far and wide who come here to savour what the beautiful KZN midlands has to offer. There is also a well-kept picnic area for day visitors who just want to unwind and enjoy the scenery.

Providing safe public access to these forests and trails is part of Sappi’s social commitment to promote eco-tourism and the local economy.

In the midst of all this, Sappi needs to operate an efficient and productive forestry operation that sustains jobs and keeps shareholders and stakeholders happy.

The Biodiversity field trip ended at the picturesque picnic spot located in the middle of a Sappi plantation, with the magnificent Karkloof Falls as the backdrop.

Biodiversity

Sappi has partnered with organisations such as the SA National Biodiversity Institute and WWF, as well as other plantation owners through Forestry South Arica, to mainstream biodiversity into the forest sector. This includes ambitious catchment management projects that extend beyond their own borders as well as the stewardship programme which facilitates the proclamation of nature reserves and protected areas on forestry land.

Sappi maintains 160 important conservation areas, including seven nature reserves, on its plantation lands in South Africa.

This work includes on-going water quality assessments and monitoring, integrated weed management plans and maintaining and enhancing soil function, a crucial component of sustainable forest management.

Forestry in South Africa is regarded as a streamflow reduction activity, and is regulated and controlled by a raft of legislation. New afforestation is restricted to catchments where spare water is available. The total planted forestry area has actually shrunk over the past 10 years or so, and is unlikely to be expanded in the foreseeable future. Plantations range in size from several thousand-hectare estates all the way down to tiny, one or two hectare plots grown by small-scale farmers located in tribal areas.

Like any crop, growing trees use water, but they use it efficiently in the production of wood fibre, a key natural resource that is renewable, sequesters carbon from the atmosphere and – unlike a material like plastic - leaves behind zero waste. Commercial forestry plantations in South Africa account for some 3% of total water use, according to an Overview of the SA Water Sector, published by the Department of Water & Sanitation. Plantations are not irrigated – they only intercept rainfall, which reduces runoff into rivers and streams. By way of comparison, agriculture/irrigation utilises 60% of total water resources in South Africa.

View of the Karkloof valley from the top of the mountains showing patches of indigenous forest, farm land and plantations.

Moreover the forest sector uses very little chemical weedicides and pesticides, the use of which are also heavily regulated by certification bodies.

So how much biodiversity can thrive in this typical patchwork plantation environment?

During 10 birding events held on Sappi plantation land in the KZN midlands between 1997 and 2007, a total of 455 bird species were recorded. A camera trap survey during the same period yielded 30 mammal species. These included jackal, caracal, civet, genet, serval, porcupine, mongoose, aardwolf, badger, otter, samango monkey, baboon, warthog, bushpig, reedbuck, bushbuck and duiker. Several sightings of leopard have also been recorded in plantations around KZN and Mpumalanga.

These sightings indicate that timber plantations – when properly managed – can play an important role in protecting and enhancing biodiversity.

A trickle of water threads through Shafton plantation at the picnic spot above the Karkloof Falls.

Last word

“Given that plantations are effectively green corridors that facilitate movement throughout the region, it is entirely possible that a land-sparing approach combining large patches of grassland in a mosaic with intensively used plantation patches provides the best compromise to produce the required volumes of wood while preserving meaningful biodiversity outside of formally protected areas.” This summation was provided by Michelle Pretorius and Justin O’Riain of the Department of Biological Sciences at the University of Cape Town, and Kirsten Wimberger of the Wild Bird Trust, in an article titled ‘Preserving large tracts of natural grassland promotes mammal species richness and occurrence in afforested areas’, published in the Forest Ecology & Management journal.

*Images & video by Samora Chapman

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

Alien invasive species a massive threat to biodiversity

Lantana camara … one of the top ten alien invasive plants that has invaded 69 regions around the world – including South Africa.

The severe global threat posed by invasive alien species is underappreciated, underestimated, and often unacknowledged. According to a major new report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), more than 37,000 alien species have been introduced by many human activities to regions and biomes around the world. This conservative estimate is now rising at unprecedented rates. More than 3,500 of these are harmful invasive alien species – seriously threatening nature, nature's contributions to people and good quality of life. Too often ignored until it is too late, invasive alien species are a significant challenge to people in all regions and in every country.

Approved on Saturday in Bonn, Germany, by representatives of the 143 member States of IPBES, the Assessment Report on Invasive Alien Species and their Control finds that alongside dramatic changes to biodiversity and ecosystems, the global economic cost of invasive alien species exceeded $423 billion annually in 2019, with costs having at least quadrupled every decade since 1970.

In 2019, the IPBES Global Assessment Report found that invasive alien species are one of the five most important direct drivers of biodiversity loss – alongside changes in land and sea use, direct exploitation of species, climate change and pollution. On the basis of this finding, Governments tasked IPBES to provide the best available evidence and policy options to deal with the challenges of biological invasions. The resulting report was produced by 86 experts from 49 countries, working for more than four and a half years. It draws on more than 13,000 references, including very significant contributions from indigenous peoples and local communities, making it the most comprehensive assessment ever carried out of invasive alien species around the world.

"Invasive alien species are a major threat to biodiversity and can cause irreversible damage to nature, including local and global species extinctions, and also threaten human wellbeing," said Professor Helen Roy (United Kingdom), co-chair of the Assessment with Prof. Anibal Pauchard (Chile) and Prof. Peter Stoett (Canada).

The authors of the report emphasize that not all alien species become invasive – invasive alien species are the subset of alien species that are known to have become established and spread, which cause negative impacts on nature and often also on people. About 6% of alien plants; 22% of alien invertebrates; 14% of alien vertebrates; and 11% of alien microbes are known to be invasive, posing major risks to nature and to people. People with the greatest direct dependence on nature, such as indigenous peoples and local communities, are found to be at even greater risk. More than 2,300 invasive alien species are found on lands under the stewardship of indigenous peoples – threatening their quality of life and even cultural identities.

While many alien species were historically introduced on purpose for their perceived benefits to people, the IPBES report finds that the negative impacts of those that do become invasive are enormous for nature and people. "Invasive alien species have been a major factor in 60% and the only driver in 16% of global animal and plant extinctions that we have recorded, and at least 218 invasive alien species have been responsible for more than 1,200 local extinctions. In fact, 85% of the impacts of biological invasions on native species are negative," said Prof. Pauchard. Examples of such impacts include the ways that North American beavers (Castor canadensis) and Pacific Oysters (Magallana gigas) change ecosystems by transforming habitats – often with severe consequences for native species.

Nearly 80% of the documented impacts of invasive alien species on nature's contributions to people are also negative – especially through damage to food supplies – such as the impact of the European shore crab (Carcinus maenas) on commercial shellfish beds in New England and the damage caused by the Caribbean false mussel (Mytilopsis sallei) to locally important fishery resources in India.

Similarly, 85% of documented impacts negatively affect people's quality of life – for instance through health impacts, including diseases such as malaria, Zika and West Nile Fever, spread by invasive alien mosquito species like Aedes albopictus and Aedes aegyptii. Invasive alien species also damage livelihoods, for example in Lake Victoria where fisheries have declined due to the depletion of tilapia, as a result of the spread of water hyacinth (Pontederia crassipes), which is the world's most widespread terrestrial invasive alien species. Lantana (Lantana camara), a flowering shrub, and the black rat (Rattus rattus) are the second and third most widespread globally, with far-reaching impacts on people and nature.

"It would be an extremely costly mistake to regard biological invasions only as someone else's problem," said Pauchard. "Although the specific species that inflict damages vary from place to place, these are risks and challenges with global roots but very local impacts, facing people in every country, from all backgrounds and in every community – even Antarctica is being affected."

The report shows that 34% of the impacts of biological invasions were reported from the Americas, 31% from Europe and Central Asia, 25% from Asia and the Pacific and about 7% from Africa. Most negative impacts are reported on land (about 75%) – especially in forests, woodlands and cultivated areas – with considerably fewer reported in freshwater (14%) and marine (10%) habitats. Invasive alien species are most damaging on islands, with numbers of alien plants now exceeding the number of native plants on more than 25% of all islands.

"The future threat from invasive alien species is a major concern," said Prof. Roy. "37% of the 37,000 alien species known today have been reported since 1970 – largely caused by rising levels of global trade and human travel. Under 'business-as-usual' conditions, we project that total numbers of alien species will continue to increase in this way."

Chromolaena odorata … another of the global top ten alien plant invaders … it is here in South Africa as well.

"But business-as-usual is actually unlikely," continues Roy. "With so many major drivers of change predicted to worsen, it is expected that the increase of invasive alien species and their negative impacts, are likely to be significantly greater. The accelerating global economy, intensified and expanded land- and sea-use change, as well as demographic changes are likely to lead to increases in invasive alien species worldwide. Even without the introduction of new alien species, already established alien species will continue to expand their ranges and spread to new countries and regions. Climate change will make the situation even worse." The report underscores that interactions between invasive alien species and other drivers of change will be likely to amplify their impacts – for example invasive alien plants can interact with climate change, often resulting in more intense and frequent fires, such as some of the devastating wildfires experienced recently around the world, releasing even more carbon dioxide into the atmosphere.

The IPBES experts point to the generally insufficient measures in place to tackle these challenges. While 80% of countries have targets related to managing invasive alien species in their national biodiversity plans, only 17% have national laws or regulations specifically addressing these issues. This also increases the risk of invasive alien species for neighbouring States. The report finds that 45% of all countries do not invest in the management of biological invasions.

On a more positive note, the report highlights that future biological invasions, invasive alien species, and their impacts, can be prevented through effective management and more integrated approaches. "The good news is that, for almost every context and situation, there are management tools, governance options and targeted actions that really work," said Prof. Pauchard. "Prevention is absolutely the best, most cost-effective option – but eradication, containment and control are also effective in specific contexts. Ecosystem restoration can also improve the results of management actions and increase the resistance of ecosystems to future invasive alien species. Indeed, managing invasive alien species can help to mitigate the negative effects of other drivers of change."

Prevention measures – such as border biosecurity and strictly enforced import controls – are identified by the report as having worked in many instances, such as the successes achieved in Australasia in reducing the spread of the brown marmorated stink bug (Halyomorpha halys). Preparedness, early detection and rapid response are shown to be effective at reducing rates of alien species establishment, and to be especially critical for marine and connected water systems. The PlantwisePlus programme, assisting smallholder farmers in Africa, Asia and Latin America is spotlighted by the report as a good example of the importance of general surveillance strategies to detect new alien species.

Eradication has been successful and cost-effective for some invasive alien species, especially when their populations are small and slow-spreading, in isolated ecosystems such as islands. Some examples of this are in French Polynesia where the black rat (Rattus rattus) and rabbit (Oryctolagus cuniculus) have been successfully eradicated. The report indicates that eradication of alien plants is more challenging due to the length of time that seeds may lie dormant in soil. The authors add that successful eradication programmes depend on, amongst other elements, the support and engagement of stakeholders and Indigenous Peoples and local communities.

When eradication is not possible for different reasons, invasive alien species can often be contained and controlled – especially in land-based and closed water systems, as well as in aquaculture – an example being the containment of the invasive alien Asian tunicate (Styela clava) in aqua-cultured blue mussels in Canada. Successful containment can be physical, chemical or biological – although the appropriateness and effectiveness of each option is dependent on local context. The use of biological control for invasive alien plants and invertebrates, such as introducing a rust fungus (Puccinia spegazzinii) to control bitter vine (Mikania micrantha) in the Asia-Pacific region, has been effective – with success in more than 60% of known cases.

"One of the most important messages from the report is that ambitious progress in tackling invasive alien species is achievable," said Prof. Stoett. "What is needed is a context-specific integrated approach, across and within countries and the various sectors involved in providing biosecurity, including trade and transportation; human and plant health; economic development and more. This will have far-reaching benefits for nature and people." Options explored in the report include considering coherent policies and codes of conduct across sectors and scales; commitment and resourcing; public awareness and engagement, such as citizen science campaigns like those promoting 'check, clean and dry'; open and interoperable information systems; filling knowledge gaps (the authors identify more than 40 areas where research is needed); as well as inclusive and fair governance.

"The immediate urgency of invasive alien species, with extensive and growing harm to nature and people, makes this report so valuable and timely," said Dr. Anne Larigauderie, the Executive Secretary of IPBES. "The Governments of the world agreed, in December last year, as part of the new Kunming-Montreal Global Biodiversity Framework, to reduce the introduction and establishment of priority invasive alien species by at least 50% by 2030. This is a vital, but also very ambitious commitment. The IPBES Invasive Alien Species Report provides the evidence, tools and options to help make this commitment more achievable."

Top 10 Most Widespread Invasive Alien Species Worldwide

Organism groupTaxonNumber of regions
Vascular plant Pontederia crassipes (water hyacinth)74
Vascular plant Lantana camara (lantana)69
Mammal Rattus rattus (black rat)60
Vascular plant Leucaena leucocephala (leucaena) 55
Mammal Mus musculus (house mouse) 49
Mammal Rattus norvegicus (brown rat) 48
Vascular plant Ricinus communis (castor bean) 47
Vascular plant Ailanthus altissima (tree-of-heaven) 46
Vascular plant Robinia pseudoacacia (black locust) 45
Vascular plant Chromolaena odorata (Siam weed)43

The number of regions where a species has been recorded and classified as invasive based on GRIIS (Pagad et al., 2022). Note this table only refers to the distribution of invasive alien species and not their impacts.

Celebrating International Day of Biological Diversity

Forestry South Africa (FSA) celebrates International Day of Biological Diversity (Monday 22 May 2023) with a video that emphasises the need to take action to conserve biological diversity for future generations and the role multifunctional landscapes can play...

The South African forestry landscape is a multifunctional environment, where grasslands, indigenous forests, wetlands, rivers and streams weave their way between the productive forestry compartments. These natural spaces provide important habitats and migratory routes for all kinds of species, some of which are endangered and others that are only found in South Africa (endemic). These natural corridors are important, enabling the free movement of species both within the forestry landscape and between conservation areas that neighbour it. When these unplanted natural areas are managed in a way that promotes biodiversity, they can play a really important role in the conservation of both individual species and whole ecosystems.

"Across the forestry landscape, there are over 170 000 hectares of grasslands, with their associated wetlands and pans, and over 60 000 hectares of indigenous forests, all of which are sustainably managed by forestry companies. Very few Agri-sector businesses would leave 30% of their landholdings unplanted, however, in forestry this is common practice and as a result, the forestry landscape is made up of a mosaic of planted compartments and natural spaces. FSA is intensely proud of the onus forestry companies place on being custodians of the natural spaces found within their landholdings and the role these are having in maintaining and preserving biodiversity." – FSA Head of Communication and Director of Research and Protection, Dr Ronald Heath.

The Forestry Sector provides the perfect example of how it's possible to incorporate environmental stewardship into a production landscape without compromising on productivity. This not only benefits biological diversity, but it also produces a patchwork landscape that provides all manner of recreational activities that benefit our mental and physical health. FSA commissioned this video in celebration of the International Day of Biological Diversity to encourage other land users to take a multifunctional landscape approach when planning their management activities. We hope this will inspire them to do their bit in conserving South Africa's precious biodiversity for future generations to come.

"We are only now realising the true extent of the impact human activity is having on our planet. The dramatic loss in global biodiversity combined with the changing weather patterns attributed to climate change, are a warning to us all that now is the time to act. Small changes make big differences and if we all take responsibility now, as individuals and companies, we still have time to reverse these worrying trends. We have gone past the point where biodiversity can be conserved in dedicated nature reserves alone, we need to adopt a multifunctional landscape approach where production landscapes are managed in a sustainable way that promotes environmental and social benefits alongside economic gains. The video illustrates this, showcasing the important role multifunctional landscapes play in the conservation of biological diversity and how adopting this approach can make a big difference", Dr Heath concludes.

Visit the FSA website: Forestry South Africa | Forestry South Africa Official Site

*Video shot and edited by SA Forestry / Green Forest Films

Massive mangrove restoration project launched in Mozambique

Around 100 million mangrove trees to be planted; total project area 185,000 ha; 200,000 tons of CO2 to be offset annually...

The largest mangrove reforestation project in Africa has been launched by Mozambique’s Ministry of Sea, Inland Waters and Fisheries (MIMAIP) in partnership with Blue Forest, a UAE-based mangrove reforestation specialist.

The project will be implemented in the biodiversity-sensitive provinces of Sofala and Zambezia, spread across 185,000 hectares of mangrove forests. It is expected that between 50-100 million trees will be planted as part of this long-term partnership. This project will offset approximately 200,000 tons of CO emissions annually, equivalent to taking 50,000 cars off the road.

Mozambique has over 300,000 hectares of mangroves along its coast, which is one of the largest tracts of mangrove forest in Africa

The partners will utilize high resolution satellite imagery, LiDAR technology and remote sensing data to identify key ‘hot spots’ where the need for restoration is highest. Artificial Intelligence (AI) algorithms will then be used to decipher the satellite data and field measurement to customize the reforestation activities in an accurate, efficient and transparent manner.

The reforestation work will be carried out in collaboration with several stakeholders tackling the issue of mangrove forest restoration in Mozambique. Public institutions such as the National Directorate for Forrest (DINAF) and the National Fund for Sustainable Development (FNDS), as well as universities and NGOs will be engaged in this flagship campaign.

The project will be financed through carbon credits that will be generated through the reforestation and conservation activities over the 30-year period of this partnership. The proceeds will be shared between the local and national stakeholders as per the guidelines set by FNDS.

Xavier Munjovo, Permanent Secretary of MIMAIP, commented: “Mozambique has over 300,000 hectares of mangroves along its coast, which is one of the largest tracts of mangrove forest in Africa. We are delighted to partner with Blue Forest and to introduce innovative technology in the way we map and restore our vital mangrove forests for generations to come.”

Vahid Fotuhi, Founder and CEO of Blue Forest, added: “Mozambique is a hugely strategic country when it comes to mangrove forests. We are thrilled to partner with MIMAIP and to work in coordination with all the public and private national and provincial institutions, as well as the local communities in Sofala and Zambezia on this historic project. Tens of thousands of people and endless marine life will benefit from this project.”

Mangroves are a rare ecosystem that support biodiversity and provide vital ecological services including coastal protection from floods and storm surges, water filtration, carbon sequestration and nursery grounds for thousands of species of fish and crustaceans.

Mangroves all around the world are under threat due to urban development and poor farming practices upstream which release excess sediment into rivers.

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 https://ferncliffe.org. 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…

Shop with purpose at https://ferncliffe.org/support/.

Support Ferncliffe via social media:
https://www.instagram.com/ferncliffeforestwilding/
https://www.facebook.com/ferncliffeforestwilding
https://twitter.com/Ferncliffe11
https://www.youtube.com/channel/UCibUFk5m_gvCg57Y46F7_7w

Grassland dynamics & bush encroachment in forestry plantations

By Lize Joubert-van der Merwe, Veldtology (Pty) Ltd
I really like grasslands. I especially like how they ripple in waves up and down hill and mountain slopes when there is an approaching thunderstorm; how they change to that rich golden color in the final sunspots just before the dark-grey, rolling thunderclouds and lightning chases you indoors; and how their inflorescences hold rain drops from the previous night like a chandelier of diamonds. My fascination with grasslands extends beyond their aesthetic appearance to also include their ecology, management, and why this matters to forestry.

Moisture and temperature shape grasslands
Grasslands are so vast that we often accept their presence as ubiquitous, yet, they are constantly changing in response to natural and anthropogenic drivers of diversity. I interpret grassland diversity from an understanding that moisture and temperature influenced broad vegetation patterns over the past few thousand years, as outlined by Frank Neumann. Did you know that the current wet-and-warm climatic period has only been around for 800-1000 years? A cooler period with less fires (more than 13 000 years ago) caused grassland to have many more fynbos elements, and we still see relics of Protea and Erica communities growing on cooler, south-facing slopes (Figure 1 above). Much later (~4600 to 3500 years ago), there was a drier period when grasslands saw an increase in karroid elements, specifically Pentzia incana (Ankerkaroo) that nowadays dominates sheep farms in the central Karoo.

In the current wet-and-warm climatic period, grasses dominate in grasslands (hence, the name), but they still have to compete with flowering forbs, trees and alien plants to remain numero uno. For this, they use various competitive strategies. Grasses keep flowering forbs at bay by rapidly growing into a dense layer that intercepts heat and sunlight from (s)lower-growing plants. This strategy to monopolize access to sunlight is quite a dicey move, because grasses are themselves not tolerant of shading. In fact, it happens in the absence of fire and grazing that build-up of leaf litter and moribund grass blocks sunlight from reaching live buds and leaves, which causes die-back of grass tussocks – a phenomenon known as ‘self-shading’. This is why fire is such an important part of grassland management. Fire is truly the exfoliating treatment that removes dead and dry cells from grasslands, so that new life can flourish.

Importantly, the ability of grasses to outgrow forbs and intercept limiting resources is directly tied to the current climate. During periodic droughts, when grasses cannot maintain their productivity levels, forbs are quite capable of recruiting successfully from seeds (Figure 2). Similarly, grasslands subjected to severe overgrazing are not able to keep forbs in check, leading to an overabundance of flowering forbs that is sometimes even visible on satellite images (Figure 3).

The role of fire
If we shift our focus to the woodies in our midst, grasses keep shrubs and trees in check by sustaining a ‘fire trap’ from which tree seedlings hardly ever emerge unscathed (Figure 4). A fire trap is essentially the fire flame zone of the grassy layer. Unlike grasses, most indigenous shrubs and trees are sensitive to fire, especially as seedlings. So, fire gives grasses the competitive edge over shrubs and trees, just like climate gives grasses the competitive edge over forbs.

Grassland with a well-developed grass layer that burns at the correct intervals (when biomass ~ 4 tons / ha) should have no problem with invading trees. However, where the grass layer is jeopardized by too frequent burning, overgrazing or shading by large trees, fire intensity will be lower with consequently less killing power to aim at invading tree seedlings. For example, in communal rangeland (with heavier grazing → less grass → cooler fires), it often happens that tree seedlings escape the fire trap and grow into bigger trees that are more fire tolerant. Shading by timber trees also play an important role in advancing bush encroachment into grassland, especially in narrow corridors of forestry plantations. In fact, shading might explain much of the ‘edge effect’ of timber on adjacent vegetation, previously reported by Prof. James Pryke.

The role of atmospheric CO2
Interrogations of the local and global drivers of bush encroachment have led to a growing consensus among researchers that elevated atmospheric CO2 levels is an important global driver of bush encroachment. The exact mechanism is still unknown, but possibilities include the fertilizer effect of atmospheric CO2 on woody shrubs and trees, or an indirect effect on soil water content and its depletion in the surface soil layers where grass roots sit. Encouragingly though, a team of researchers led by Prof. Sally Archibald and Prof. William Bond found that bush do not encroach as rapidly in protected areas with elephants – the big giants of Africa that create their favored grassland habitat by pushing over trees. Although I am not advocating for the introduction of elephants to eradicate bush, this shows that local actions can trump global drivers in shaping vegetation dynamics. This is indeed encouraging.

Practical solutions customized to local context
The trick is to find practical management solutions that can be applied in forestry plantations to help control bush encroachment. Such solutions will probably involve a combination of management actions sustained for longer periods of time, rather than single once-off interventions. For example, it would be pointless to do a once-off clearing of dense stands of Ouhout trees, with no follow-up burning and thinning operations to keep shrubs and trees in check. Moreover, instead of looking for a silver-bullet strategy that works well everywhere, management actions would probably need to be customized to fit local context and challenges.

Key local issues will include the shape and size of conservation areas. By virtue of their close proximity, any management intervention inside a narrow, small or irregularly-shaped conservation area has a greater probability of affecting adjacent timber compartments, than if you had a wider or larger conservation area. Thus, when a decision has to be made to control bush encroachment in one conservation area (but not another), shape and size is a useful starting point. In fact, it is non-negotiable that the conservation area must be the correct shape and of reasonable size to allow for safe burning.

Additional considerations include proximity to important conservation areas (e.g., with Red-Listed species or threatened ecosystems) and level of wetness. If bush encroachment threatens the functionality of a threatened grassy ecosystem, this is a good reason to prioritize bush thinning operations. Even more so when that threatened ecosystem contains threatened species, such as Long-toed Tree Frogs (Leptopelis xenodactylus), Swamp Nightjars (Caprimulgus natalensis) or African Grass Owls (Tyto capensis) that all depend on grassy habitats.

Lastly, level of wetness seems to influence vegetation succession (grassland -> bushy thickets or forest) and / or how the wetland ecosystem responds to bush thinning and burning. This is beautifully shown in the delineated areas of Zululand, where wetter wetlands have a greater tendency to remain grassy, whereas drier wetlands have a greater tendency to become bush encroached. We do not quite understand the mechanism of this phenomenon - it might be that grasses (with shallower roots) respond quicker than shrubs and trees when there is a shallow water table present. If this is the case, it will mean a better ecosystem response to burning, because a healthy grass layer is better able to sustain a fire trap that kills tree seedlings. Personally, I would consider shortlisting wetter wetlands for bush thinning and burning.

The role of roads in shaping fire
It makes logical sense that all management operations should be aligned with clearly-visible, on-the-ground features so that operators know where to work. Such features can be roads, trace belts, streams or fence lines, depending on what is available. Where fire management is concerned, roads (mostly vegetated or dirt tracks) work exceptionally well, because they also provide access to vehicles and fire-fighting equipment, and should have low fuel loads (due to routine road maintenance). This makes it possible for foresters to set alight vegetation along the road, so that the fire burns from the periphery towards the interior of a conservation area, with minimal risk to adjacent timber. This is probably why we find grassland vegetation in larger conservation areas with roads along their edges, but bushy thicket in those without roads (or wrongly placed roads) (Figure 5). Exceptions include narrow or irregularly-shaped conservation areas that will probably not burn, regardless of presence or absence of roads, because of risk to adjacent timber. Another exception is conservation areas on steep slopes, where management (also roads placement and burning) would be adjusted to fit the soil erosion risk profile.

The value of well-placed roads is not new and already embedded in wetland delineation procedures for some forestry companies. Especially in Zululand (where terrain is not a problem), valley-bottom cut-off roads are routinely implemented at the edge of conservation areas (where they join commercial timber) to mark new compartment boundaries, to provide access, and to enable the use of fire in alien plant control (Figure 6). Getting control of alien plants within the first few years after felling timber is a major delineation goal, because it feeds into water security and sets the direction of ecosystem recovery in terms of biodiversity. Most of the roads around conservation areas have vegetated surfaces and are not expensive to maintain (Figure 6), but they make the world’s difference in restoring delineated land to a semi-natural state.

I think many environmentally-minded people (including myself) have been blinded by the negative impacts of roads, notably in connection with soil erosion and sedimentation. Perhaps, it is time to recognize that well-designed road networks (with roads that are well-placed, well-drained and well-maintained) can be conservation assets too.

Using fire in alien plant control
Fire, along with foliar herbicide sprays and cut-stump applications are your cost-effective tools in the fight against alien plant invasions, notably American Bramble. Of these, fire followed by foliar sprays is the most cost-effective treatment option available in grasslands, but it is seldom (if ever) used in dense thickets.

Fire in grassland simplifies access, reduces the size of alien plants and causes a flush of new growth, which is more susceptible to foliar sprays than stems and mature leaves (Figure 7). However, of critical importance is the timing of post-fire follow-up sprays to hit the flush of new vegetative growth just at the right time, i.e., when plants are between knee and hip height. Get the timing wrong, and it is back to square one. No alien plant control operation should start without a viable follow-up plan that can be implemented with available resources - money, manpower and the necessary expertise to guide effective alien plant control.

Different stages of bush encroachment
Bush encroachment is a gradual process of indigenous shrubs and trees replacing grasses often over a period of >10 years. Drought with uncontrolled grazing and shading of the grass layer in narrow corridors can increase the rate of bush encroachment, while expeditious burning can delay or stop the process. At the end of the day, there will be different stages of bush encroachment in a forestry landscape, with at least some alien plants that need to be controlled.

Early stages of bush encroachment (when shrub and tree cover is still sparse) should be prioritized for intervention, because the cost-effective management of alien plants with fire and foliar sprays is still possible. Basically, foliar sprays can be used until alien plants are about shoulder height, but do remember that bigger plants → more herbicide → greater cost. For alien plants above shoulder height, cut-stump applications are your next-best option, but at a far greater expense. Even larger specimens can be frilled or ring-barked, which are labor-intensive and time-consuming operations. Here, you must ensure it is done correctly to ensure maximum effectiveness.

For late stages of bush encroachment (dense thicket or early-successional forest), a different mechanism is used to effectively control alien plants. Here, the tree canopy effectively intercepts sunlight from reaching the soil surface, which prevents alien seeds from germinating. Dense thickets with an intact tree canopy generally do not have a problem with alien plants. It is only where there are gaps in the canopy (due to windfall or along thicket edges) that alien plants can establish, and where they need to be controlled.

A word of caution, though. Chopping down a large, solitary pine or eucalypt tree inside a dense thicket patch will create a gap in the tree canopy that presents an opportunity for alien plant recruitment. It is better to ring bark or frill such trees, so that surrounding indigenous trees are not damaged and so that there is not a sudden flush of sunlight available at the forest floor. The longer ‘time-to-kill’ for ring barked or frilled alien plant specimens also leaves a window of opportunity for indigenous tree species to fill the tree canopy gap, which effectively removes the alien plant recruitment opportunity. The effective control of alien plants in dense thickets considers treatments along with this careful manipulation of shade and sunlight on the forest floor.

In contrast to early and late stages of bush encroachment, there is an intermediary bushy state that presents a problem to management, and also has less biodiversity value than both more-grassy and more-forested states, according to Dr. René Gaigher. Here, fire cannot be used anymore (due to lack of grass cover) and the tree canopy has not yet locked out sunlight. This stage is susceptible to alien invasion, but it is difficult to gauge extent of invasion due to poor visibility and accessibility. For the same reasons, alien plants are difficult to find and treat. Viable treatment options in this context are expensive and time-consuming: cut-stump applications and frilling. Foliar herbicide spraying is an option along edges, but cannot be recommended for the interior of these bushy patches.

Where it makes sense to do so, the long-term strategy to control alien plants would be to reverse the intermediary bushy state back to grassland, so that fire and foliar spraying can again be used as treatment options. This will also benefit biodiversity. However, it will be an expensive and difficult journey of sustained effort for many years, which necessitates careful consideration of the points raised earlier (size and shape, important conservation areas, slope direction, and level of wetness). For all other conservation areas that is still in a predominantly grassy state, it is of utmost importance to maintain that grassy state with appropriate management.

Grassland for water production
Probably the greatest benefit of functional grasslands in conservation corridors involves their ecological function in the sense of water production. Grasslands use less water than bushy thickets, and much less than alien vegetation. According to the National Water Act (Act 36 of 1998), commercial forestry is a stream-flow reduction activity that requires a water use license to safeguard national water security. It is this legal framework that enforces wetland delineation and control of alien plants along waterways, but it does not stipulate desired natural vegetation type (grassland vs. bushy thickets vs. forest) once timber along streams and around wetlands is felled. If the objective of legislation is to safeguard water security for downstream users, it would seem advantageous to have more grassland and less bushy vegetation in riparian and wetland buffer zones.

However, conservation corridors are not just water production areas. They also conserve biodiversity and ecosystem function, specifically ecological values representative of the historic state before timber dominated these landscapes. If the historic state in Zululand is coastal forest along streams, with grassland a bit further way, there is no reason for bush thinning operations in the riparian zone. Burning of grassland adjacent the forested riparian zone will maintain a functional ecotone and ensure that the coastal forest do not expand to dominate the entire drainage line. Maintaining this natural range of habitat types (grassy and woody types in wetter and drier areas) will tick the ‘biodiversity conservation’ block along with the one for water production.

A bit of practical wisdom also goes a long way for the management of rugged, south-facing, bush encroached hillslopes in the KZN Midlands. If the terrain is too rugged to have roads (to help safe burning) and if the microclimate on that hillslope is too cold and wet to sustain a fire, it might be best not to intervene with bush thinning operations. However, conservation areas on warmer hillslopes that jut down to rivers and with bush encroachment that can be traced back to a clear starting point (such as a change in ownership or retirement of an experienced forester) are good candidates for bush thinning operations that will probably also benefit water production.

Lize Joubert-van der Merwe is an independent consultant specialising in sustainable agriculture and forestry through improved management of natural resources.

Drone-mounted tool for sampling tree canopies

A University of Sherbrooke research team specialising in aerial robotics has developed a self-powered, drone-mounted tool that is able to collect foliage samples from high up in tree canopies, according to a report from Friday Offcuts.

The DeLeaves canopy sampling tool is suspended beneath a drone, is equipped with an HD camera, and has two robotic arms to collect foliage samples from trees.

The tool was first used by a group of horticulturists to sample foliage from tropical forests in Vietnam.It has been deployed by the Canadian Airborne Biodiversity Observatory to study the spectral and functional trait differences within tree crowns; and has been used to sample Douglas Fir, Silver Firs, and Western Hemlocks by the National Ecological Observatory Network team.

Since then it has been used to collect samples of tree canopies in North America and Europe. It has further potential for crop sampling in agriculture. The DeLeaves canopy sampling tool will be showcased at the ForestTECH 2021 event being run in Rotorua, New Zealand in November.

Source: Friday Offcuts
Visit: www.foresttech.com