How to fix up our rivers so they become assets
By Georgina van Biljon
Post created 2023-07-06
In this article I will be explaining what is river rehabilitation, why it is important and how to go about it.
Photo above left: Klein Berg River rehabilitation site near Tulbagh (Photo taken 2022); Photo above right: The same rehabilitation site after a fire swept through it and (photo taken in 2013). Since planting in 2013, a total of 280 indigenous plant species has been used in this project.
Fresh water is one of the greatest natural assets in our water-scarce country. Most of our rivers are in a poor state (with 84% of South Africa’s rivers being in a moderately to extremely modified condition - State of Rivers Report (2019)). Apart from poor water quality, rivers are heavily invaded with invasive alien plants (IAPs) that out-compete our native indigenous plants due to shading.
Local soil erosion increases in areas densely invaded by alien trees, as the ground cover that provides surface stability is excluded by the alien canopy (Holmes et al. 2005). As the soil gets washed away, riverbanks can become steeper and more deeply channelised ('incised') , especially in lowland rivers. This in turn can increase the river flow velocity, further aggravating the erosion potential. These alien trees are termed ‘transformer species’ as they disrupt and transform entire ecosystems. While IAPs are a serious threat to our freshwater ecosystems, they are not the only one. We also dump pollutants and rubble, reshape riverbanks with excavators, remove indigenous plants and let our livestock overgraze and cause erosion on stream banks, also known as ‘dongas’.
What can we to do about it?
River Rehabilitation is a means to address these issues mentioned above, by trying to undertake ecosystem repair and function. So that it can return to a near natural state as possible. Ecological restoration is 'the process of assisting the recovery of an ecosystem that has been degraded, damaged or destroyed' (SER). These definitions are further explained by the Society for Ecological Restoration (SER) on this link: https://www.ser-rrc.org/what-is-ecological-restoration/ and SER has also provided international principles and standards for the practice of ecological restoration: https://www.ser.org/general/custom.asp?page=SERStandards
Removal of invasive plants:
The biomass of the invasive trees can be very useful. It has a variety of potential uses, including wood chips, biochar, firewood or other wood products like pulp or timber for furniture or construction. It is worth bearing in mind, however, that environmentally whatever one removes out of a system, such as carbon for example, one should try to replace. Removal of category 1 invasive alien plants (IAPs) from one’s property is required by law [NEMBA Act (2004) and the NEMBA Regulations (2014)]. The reason for this is not only to release more water into our rivers, but to protect our unique biodiversity - which is our natural capital. IAPs compete for our precious natural resources and ultimately transform our land. “Secondary invasions” can occur after the removal of the primary invasive alien species from an area. This is because these secondary invasive species are able to capitalise on the disturbances caused to soil chemistry by the primary invaders as well as by the openings caused during the removal of the primary invader species. To overcome this issue, one needs to sow and/or plant indigenous plants as soon as possible after initial clearing to help out-compete the invasive plants. There are some indigenous grasses and fast-growing pioneer plants that can help with this. However, over time one should have a plan to re-establish the appropriate ecosystem (with both pioneer and longer-lived species) which can boost the natural capital of the riverbanks/ riparian zone.
What is ecological infrastructure (natural capital)? Ecological Infrastructure refers to the goods and services that the environment provides for us (for free). By way of example, by planting and establishing palmiet (Prionium serratum) in the wet zone of a river, one helps to reduce the speed of the river, reducing the erosive ability of the water during flooding. It also helps to filter and clean the water due to its dense, mesh-like structure of old leaves that trap sediments (Rebelo et al. 2019). The amount of water lost through A-Pan evaporation (from the surface of the water) is more than what is lost through transpiration of palmiet (Rebelo et al. 2020).
Photo above: palmiet (Prionium serratum) roots in a clear water stream near Waterval Nature Reserve, Tulbagh.
There are multiple benefits associated with establishing the appropriate indigenous plants along riverbanks. Increasing and investing in a biodiverse landscape may act as a buffer against climate change and help to counteract impacts of extreme weather conditions like flooding. In other words, increasing biodiversity also increases the system’s ability to absorb and adapt to stresses. Other benefits of rehabilitation are habitat creation for pollinators, which support fruit production in adjacent agricultural landscapes. Likewise, an increase in predatory insects that can take refuge in these biodiverse rehabilitated areas can act as natural pest control against aphids and other agricultural pests. Soil micro-organisms (like Collembola) thrive in healthy ecosystems and boost soil health. Restored riparian zones act as corridors for the movement of species across a landscape. These interconnections across landscapes also strengthens ecosystem resilience.
Rehabilitation sites can be an attraction for eco-tourism, walking trails and birding. In the pictures above, our staff constructed walking trail through a rehabilitation site along the banks of the Berg River. Below is a nest discovered on a rehabilitation site, while conducting research into plant survival.
So how does one go about rehabilitating riparian zones?
Firstly contact a rehabilitation specialist to assist in developing a tailor-made plan according to your site conditions.
Riparian zones are highly dynamic (constantly in a state of change), and one needs to have holistic understanding of geomorphology, hydrology, botany and horticulture in order to restore it. Attempting to do it oneself may seem like a less expensive option but can lead to some regrettable issues and ultimately end up costing considerably more than professional advice upfront. Remember, experts have had years of experience in the field, over which time they have learned many lessons that help ensure the success of subsequent projects.
Johann van Biljon, founder of Intaba Environmental Services (with over 17 years of experience in rehabilitating rivers) talks about this issue:
“We have worked with over 50 landowners undertaking river rehabilitation over the last 10 years. One landowner unfortunately planted bottle brush trees (Callistemon viminalis) after alien clearing had already taken place.”
These trees are a listed IAP, so utterly inappropriate as a restoration species (not to mention unlawful).
“Another landowner planted hundreds of indigenous trees on second hand drippers from his vineyard and lost nearly all his trees due to irrigation failure in summer”.
Fortunately, Intaba has provided a few practical pointers to help guide landowners in their river rehabilitation endeavors.
How to undertake riparian rehabilitation:
Understand the ecosystem drivers
What 'forces' cause change in the environment? What are the anthropogenic (caused by people) and natural drivers? Understand the climate, hydrology, soil and human activities in the area.
Eradicate your invasive plants and remove threats to rehabilitation efforts. Learn about IAPs (see resource links below) and ensure that you follow alien clearing methods that are recommended on the ‘Working for Water’ website. Specific herbicides & dosages are registered for different plant species and growth forms, stick to these specific chemicals and dosage rates. If you are not sure how to identify the plant species, use an app like iNaturalist, check out PlantZAfrica, consult your local Department of Agriculture representative or contact SANBI’s Directorate of Biological Invasions. Understanding the potential threats to your rehabilitation efforts is key: are there livestock overgrazing the riparian zone? Are there too frequent fires? Is there an altered hydrology, due to over abstraction? Find out the cause of the degradation, what is driving it and whether it may be mitigated.
Understanding riverbank dynamics, flooding and local systems is necessary, as there are different zones along a riverbank, secondary channels and various other hydrological and geomorphology aspects that need to be considered when rehabilitating riparian zones. Certain plants are suited to the wet bank zone and can be completely under water in flooding season, while others are better established in the dry bank zone that is flooded only rarely, e.g. during a 1:20 year flood event. Seek to understand the ABIOTIC (climate, soil, etc.) and BIOTIC FACTORS (vegetation type, keystone species etc.) in the system, as they all have an influence on how you undertake rehabilitation. The more you know about your natural environment the more you will be able to best navigate the task ahead.
Reshaping of modified or unnaturally shaped riverbanks (caused by erosion or the historical use of machinery) is sometimes necessary, but a challenge to correct. Just keep in mind that re-shaping of riverbanks can only be done through authorisation via Dept. of Enviro Affairs. This application can only be done through a registered Environmental Consultant and a Freshwater Specialist.
Photo above: Intaba was given authorization to re-shape a river bank into a more natural shape. (Photo taken 2021)
Planting methodology: Intaba has found that a combination of sowing of indigenous seeds and planting seedlings gives the best results in rehabilitating river banks. This also depends on your budget, site conditions and plant material available. If seeds are to be used, one needs to understand sustainable harvesting methods, timing of seed maturation, seed treatment and germination methodologies in order to maximise successes. A permit from Cape Nature is needed to collect seed and plant material from natural areas. Plant selection and sourcing is further described below.
Photo above: a combination of sowing and planting occurred on this rehabilitation site. Overhead irrigation was used instead of drip irrigation, as we were unsure of the filtering of the water that was to be used. (Photo taken 2021)
Timing of planting/sowing is also crucial. Planting and sowing are best done at the beginning of the rainy season, so that the plants have enough time to establish a good root structure to survive the dry season. However, if you have good irrigation and water supply, this can be manipulated. IAPs are very good at colonising disturbed ground, so it is best to plant and sow indigenous plants as soon as possible after IAPs have been removed in order to minimize the second wave of IAP infestation and/or secondary invaders from establishing.
Plant selection is a crucial aspect of riparian rehabilitation. One should only use local indigenous plants that occur naturally in the same river catchment, in the same riparian habitat and within the same specific soil type as on the rehabilitation site. This is necessary to preserve genetic integrity of plant species in the rehabilitation site and within the river itself. You don’t want to introduce a plant species that doesn’t naturally occur in that ecosystem, as they can potentially be invasive and out-compete the local plants. A local freshwater ecologist/botanist or riparian rehabilitation specialist should be able to devise a suitable plant list for you. There are a few specialist rehabilitation nurseries and companies in the Western Cape, see list below.
Sourcing of plants: One cannot easily find locally sourced plants on the market. Most plants that are produced in commercial nurseries are grown to look great, but may not be adapted to surviving in more harsh conditions. Many so-called “indigenous” species are hybrids of natural varieties that may, in fact, pollute the genetics of subsequent generations and even affect their wild relatives. It is best to ask a Rehabilitation Specialist where to source the right plants.
Irrigation is recommended for achieving higher success rates for active planting of plants on riverbanks. Preferably in-line drippers, as they are more reliable and don’t require much maintenance. Irrigation is needed in the first year to help the young plants survive over the dry months.
Soil additives will also help with the establishment of plants in eroded and degraded river systems to boost soil organic carbon. This is especially important if IAPs biomass was removed from the rehabilitation site (taking its stored carbon with it). One must use good quality organic compost, as pathogens and weeds that survive in second-rate compost can become an issue. Inoculated biochar is also another alternative that boosts soil health, but it is best to inoculate your biochar with local micro-organisms sourced from pristine habitats as close to the rehabilitation site as possible.
Fortunately, there is a global drive to restore degraded ecosystems (the UN have just launched the Decade on Ecosystem Restoration 2021-2030), with potential funding and support. There are some subsidised/semi-subsidised programmes and organisations which are working on restoring rivers in South Africa, namely DEA&DP (WC Dept. of Environmental Affairs and Development Planning), WC Dept. of Agriculture (LandCare), SANBI, FSC – ReforestAction, GreenPOP, Wildlands are but a few. There are also global organisations like the Society for Ecological Restoration (SER) that have devised global standards for restoration and have resources to assist people and organisations in devising restoration plans. The SER are developing an African Chapter and have provided a list of Restoration Practitioners (Restoration Directory) on their website.
In order to restore degraded ecosystems and rivers, one needs to have a vision that it is never to late to make a change for the good. We are part of our environment and our future depends on it.
Photo above: a rehabilitation site near Tulbagh in its initial phase. Fences were erected to keep livestock out, as the site was heavily overgrazed. (Photo taken in 2022)
Web Resources:
Society for Ecological Restoration (SER): https://www.ser.org/ Invasive Alien Plants(IAPs): www.invasives.org.za https://www.environment.gov.za/projectsprogrammes/wfw Indigenous plants: http://pza.sanbi.org/ iNaturalist: https://www.inaturalist.org/
Cape Farm Mapper: https://gis.elsenburg.com/apps/cfm/
Rehabilitation Nurseries/Contractors/Specialists in the Western Cape (per location): Prince Albert: Renu-Karoo Nursery(Sue Milton)
Tulbagh: Intaba Environmental Services (Johann van Biljon)
Stellenbosch: Envirowise (Lynda Muller)
Worcester: Landcare Field Reserve & Nursery; Karroo Botanical Gardens
West Coast: Vula Environmental Services; Veld & Fynbos Nursery
Cape Peninsula – Cape Ecological Services (Patricia Holmes)
Good Hope Gardens Nursery; Cape Flats Fynbos Nursery; Urban Landscape Solutions.
Overberg: Green Futures Nursery
References:
Holmes, P.M., Richardson, D.M., Esler, K.J., Witkowski, E.T.F., Fourie, S. (2005) A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa. South African Journal of Science. 101, 553-564.
Rebelo, A.J., Jarmain, C., Esler, K.J., Cowling, R.M., Le Maitre, D.C. (2020) Water-use characteristics of Palmiet (Prionium serratum), an endemic South African wetland plant. Water SA 46(4) 558-572.
Rebelo, A.J., Morris, C., Meire, P. & Esler, K.J. (2019) Ecosystem services provided by South African palmiet wetlands: A case for investment in strategic water source areas. Ecological Indicators 101, 71-80.
Thirion, C., Jafta, N. (2019) State of the rivers report; River Ecostatus Monitoring Programme. Department of Water and Sanitation. https://www.dws.gov.za/iwqs/rhp/state_of_rivers/annual/State_of_Water_2017_2018_hydro_year_updated_FINAL_2019_10_11_web.pdf