Care and management of natural capital
IMPACT OF ALIEN INVASIVE PLANTS
South Africa is a water scarce country, “every year an estimated 1.44 billion m3 of water is lost to invasive alien plants(IAP’s) in South Africa. To put it in perspective, this amount of water loss is enough to provide 3.38 million households with four inhabitants with water for a year or to irrigate 120 000 hectares of cropland”. Invasive alien plants also out-compete and displace indigenous species, cause habitat degradation and disrupt ecosystem functioning by transforming the ecology of the area they inhabit. They also increase the risk and intensity of wildfires.
There are two processes of alien plant invasions, expansion and densification, where existing stands of IAP’s spread by dispersal, particularly along seed dispersal vectors, such as paths, roads and seasonal and perennial watercourses, which is then followed by the densification of new colonies. Since the 1650’s most alien species were introduced for agriculture, horticulture or for forestry. Many weeds have been introduced accidentally with fodder imported from Argentina for horses during the Anglo Boer war. Problem woody species, such as pine, eucalyptus and poplar (introduced for poles for construction, infrastructure and mining) continue to spread from source plantation, while black wattle (introduced for leather tanning), syringa and jacaranda (introduced ornamentals) have subsequently naturalised (Hoffman & Ashwell, 2001).
Herbacous species that invade grassland areas degrade habitat and reduce grazing capacity by displacing indigenous grass species. The following invaders threaten grasslands in the Magaliesberg Biosphere and efforts must be made to control them: Verbena bonariensis – Wild Verbena and Campuloclinium Macrocephalum – Pom pom weed.
CONTROL OF INVASIVE ALIEN PLANTS
The control of invasive alien plants is necessary to protect our biodiversity and water resources.
The Alien and Invasive Species Regulations of the National Environmental Management: Biodiversity Act 10 of 2004 (NEMBA) categorizes invasive plant species into four different categories, and requires that landowners are legally obliged to control invasive alien plants occurring on their properties.
Invasive plants requiring compulsory control. Plants are to be removed and destroyed.
Permits must be issued for these plants to be kept on a property, and their management and control must be in terms of an approved invasive species management plan.
Declared invader plants with a commercial or utility value. They are not permitted within 30m of the 1:50 year floodline of a watercourse or wetlands unless authorised by the Department of Water Affairs.
Primarily ornamental or ‘exotic’ horticultural plants that have escaped from gardens. Eradication of existing plants is not required, except within 30m of the 1:50 year floodlines of watercourses or wetlands, where any category 3 species must be regarded as category 1b. The spread of these plants must be prevented and they may not be planted.
Three different control methods are used for IAP control: mechanical, chemical or biological control methods. The methods used will depend on the species, size and age of the plants.
MECHANICAL CONTROL : The physical destruction or total removal of plants (e.g. felling, strip-barking; ring-barking, hand-pulling and mowing).
CHEMICAL CONTROL : Foliar spraying of herbicides to kill targeted plants. Gel (e.g. Kaput) stump applications are generally less toxic to surroundings than foliar sprays or liquid/diesel applications.
BIOLOGICAL CONTROL : Involves the release of natural enemies that will reduce plant health and reduce population vigour to a level comparable to that of the natural vegetation.
Using a combination of at least two of these methods may be required, and repeated follow up ( every 6 weeks) with mechanical and chemical control to remove seedlings and coppiced foliage is necessary.
The National Alien Invasive Plant Survey (Kotzé, et al., 2010), identifies 27 prominent invasive woody species nationally of which 11 occur in the Magaliesberg Bisphere.
|Species||Common Name||Invader Category||Control Method|
|Acacia mearnsii/dealbata/baileyana||Wattle||2||M, C|
|Arundo donax||Spanish reed||1||M|
|Cereus jamacaru||Queen of the night||1||Biological control – Thrips sp. released in Magaliesberg|
|Salix babylonica||Weeping willow||2||M,C|
|Opuntia spp.||Prickly pear||1||C|
(Source Kotzé, et al., 2010; Department of Environmental Affairs, 2014)
IMPACTS OF WILDFIRES
Fire as an ecological factor, is an essential part of the savanna and grassland biomes. Over millions of years fire tolerant and fire dependant species have evolved in the presence of fire. On the Highveld, lightning is responsible for about 20% of wild fires, the balance being anthropogenic ignitions. However, fire intensity, pattern and spread in grassland and savanna landscapes is limited by seasonal variations in fuel-load and fuel (biomass) moisture rather than by ignition frequency (the opposite applies for forest biomes) (Scholes, 2012; Govender, et al., 2006) Detrimental effects of fire have been noted with respect to some faunal species, specifically reptiles and in riverine and forest vegetation that is not fire tolerant (Van Oudshoorn, 2012).
Data from the Pilanesberg Game Reserve (typically savanna bushveld close to the Magaliesberg) indicates approximately a third of the area is burned annually, with a larger fraction being burned after a good rainy season (the average being ±600 mm).
This indicates a climatological influence on fire intensity and spread. Studies also find that fire frequency also influences fire intensity, where results show a decline in fuel load only after the sixth year post fire (Smith, et al., 2012; Uys, 2004).
In savanna vegetation, variation in fire intensity is seen as an essential factor in maintaining the grass/tree matrix. Intense fires result in tree mortality and reduced recruitment to adult sizes.
In grasslands the exclusion of fire for >10 years can result in compositional changes, such as bush encroachment in grasslands. In terms of biodiversity, grassland forbs appear to be particularly resilient to any fire regime while dominant grasses showed a strong response to season and frequency of burn which could support the suggestion that repeated fire in the wrong season can lead to veld deterioration over the long term. Further studies show a burn interval of 1 to 5 years maintains fire tolerant species and species richness, with perhaps a longer interval required to maintain species with low fire tolerance. The effects of fire exclusion on both tolerant and low-tolerance species, needs further study(Uys, et al., 2004;Van Oudshoorn, 2012; Smith, et al., 2012).
Traditionally veld management for fire was related to maximising grazing capacity with hot fires applied to combat woody encroachment to pasture and 2-3 year burn cycles to coincide with the flowering cycle of grasses. Fire was also used to remove moribund to improve grazing, and to provide early season green-bite grazing (Govender, et al., 2006; Scholes, 2012;Van Oudshoorn, 2012).
To date, the effects of fire on all savanna and grassland biodiversity is still poorly understood, and so are the long term effects of changing fire regimes .Recent suggestions focus on flexible fire regimes or “pyrodiversity” in these biomes, to encourage a variety of fire-types and a spatial and temporal randomisation of fire regimes over the long-term (Smith, et al., 2012; Scholes, 2012).
As a landowner, you are responsible for the prevention and management of all fires that occur on your land, in terms of the National Veld and Forest Act 101 of 1998. If you and your neighbours form a Fire Protection Association (FPA), it will help you to comply with these regulations. An FPA is an organisation formed by landowners to predict, prevent, manage and help fight wildfires in a particular area.
Some advantages of an FPA is that “no presumption of negligence” can be used in civil proceedings due to fire damage if you belong to an FPA, even if the fire started on your property. Furthermore, resources can be combined more effectively with other landowners to manage fires more effectively. Firebreaks can also be placed where it is best for the area as a whole, not just for one property.
Have a good fire management plan in place and be sure you have identified the high-risk areas on the farm and have preventative measures in place. Maintain your fire breaks as well as access roads and have an emergency procedure in place. Make sure it is communicated to all staff. Also, remove alien vegetation on the farm as alien infested areas pose a higher fire risk than the indigenous [vegetation]. After a fire, in areas where there were heavy alien infestations, you have a window of opportunity to clear alien vegetation at a much lower cost. (Justin Lawrence, Cape Nature)
Fire Management tips
- Ensure that fire-fighting equipment is maintained and in good working order before the start of each fire season.
- Ensure that staff is trained and adequately equipped to fight runaway fires.
- Set up or join a community group for monitoring , reporting and rapid response to fire events.
- Obtain the necessary permits and inform property neighbours, your fire protection association (FPA) and local municipality fire officers of your intention to burn at least two weeks prior to the event.
- Keep accurate records of fires, using a map of veld age as a basis. Note the date and time of ignition, weather conditions, etc.
- Make sure houses have large areas cleared around all buildings.
- Investigate fire insurance options
IMPACTS OF EROSION
Erosion by wind or water occurs when the soil lacks protective cover, such as bare or tilled lands.
Water or wind dislodges and removes particles of soil from the surface, mostly by a fairly uniform removal of topsoil called sheet erosion, but sometimes in a concentrated flow of water forming rills and gullies, landslides and stream bank collapse. Erosion Gullies or “Dongas” are a sign of severe erosion.
Erosion reduces the productivity of the land by reducing water infiltration, soil organic matter, soil nutrients, and soil depth which diminishes the diversity of plants animals and microbes, and threatens the stability of ecosystems. Badly eroded agricultural fields are often abandoned and replaced by converting areas of natural vegetation to agriculture, which places more strain on intact biodiversity resources (Pimentel & Kounang, 1998).
The natural rate of erosion in undisturbed vegetative cover is between 0.02 and 0.75 tons per hectare per year, depending on rainfall erosivity, slope and the physical characteristics of the soil. This rate can increase to 25.7 tons /ha/yr for bare soil and 5.9 tons /ha/yr for rotational mixed cropping (Hoffman & Ashwell, 2001). In general the extent of the Magaliesberg region is classified as med-low erosivity risk according to the type of soils present and taking slope into account (AGIS, 2007).
PREVENTING SOIL EROSION
Some of the following measures can be implemented to prevent soil erosion:
- The use of contour ploughing and windbreaks
- Leave unploughed grass strips between ploughed lands (strip cropping)
- Make sure that there are always plants growing on the soil, and that the soil is rich in humus
- Avoid overgrazing
- Allow indigenous plants to grow along riverbanks
- Conserve wetlands
- Cultivate land using a crop rotation system
- Minimum or no tillage
- Encourage water infiltration and reduce water runoff ( Agric.za 2008)
Remediating a gully is a labour intensive and costly exercise. Some general strategies needed to remediate and control gully erosion:
- Modifying the catchment or slope to reduce or redirect runoff.
- Stabilize gully heads, floors and walls with built structures, earthworks, vegetation, woody biomass or rocks and fencing.
- Remove access for livestock, game, 4×4 vehicles, quadbikes and motorbikes.
- Revegetate surrounding land as much as possible.