Erosion and Sediment Yield in Relation to Afforestation and Fire in the Mountains of the Western Cape Province, South Africa

Scott, David F.; Versfeld, D. B.; Lesch, Walter

doi:10.1080/03736245.1998.9713644

Cited by 80 publications

(62 citation statements)

References 18 publications

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“…The increased intensity of fires in invaded areas makes them more difficult to control (Chandler et al, 1983). The increased severity of the fires also results in greater damage to soils through heating and combustion of the organic matter which, in turn, can result in water repellency and severe soil erosion (DeBano and Rice, 1973;Giovannini and Lucchesi, 1983;Scott andVan Wyk, 1990, 1992;Scott, 1993;Scott et al, 1998b). The risk of severe flooding is also increased by the increased surface runoff and higher peak flood water volumes (Scott et al, 1991).…”

Section: Other Benefitsmentioning

confidence: 99%

Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management

Maitre¹,

Wilgen²,

Gelderblom³

et al. 2002

Forest Ecology and Management

239

136

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Invasive alien plants are consumptive water-users, and may have reduced river flows in South Africa by about 6.7% according to a broad-scale study. An effective programme to bring the invasions under control would cost about US$ 92 million per year for the next 20 years. This paper reports on studies of four representative catchments (the Sonderend, Keurbooms, Upper Wilge and Sabie-Sand) to assess the impacts and costs of invasions at a scale that is more relevant to managers. Several alien plant species have invaded the catchments. Non-riverine invasions are mainly Pinus and Hakea species in Sonderend and Keurbooms, eucalypts in the Upper Wilge, and pines and scramblers (e.g. Lantana camara) in the Sabie-Sand catchment. Riverine invasions are dominated by Acacia mearnsii and, to a lesser extent, A. dealbata, except in the Sabie-Sand and the lower Sonderend River where Eucalyptus species are important. About 44% of the Sonderend, 54% of the Keurbooms, 2% of the Upper Wilge and 23% of the Sabie-Sand catchments has been invaded to some degree. The corresponding reductions in the natural river flows attributed to these invasions are about 7.2, 22.1, 6.0 and 9.4%. If the invasions are not controlled they could potentially spread, and occupy 51, 77, 70%, respectively, of the first three catchments. At an annual expansion rate of 10-15% this would take about 13, 26 and 63 years, respectively. The invadable areas in the Sabie-Sand catchment are already invaded so invasions will only increase in density. It would take about 26-30 years to reach 100% canopy cover. The projected flow reductions for the four catchments would increase to 41.5, 95.5, 25.1 and 22.3%, respectively. The estimated cost of the control programmes to prevent these losses would be about US$ 13.2, 9.9, 4.1 and 6.6 million for the Sonderend, Keurbooms, Upper Wilge and Sabie-Sand catchments, respectively. Should the catchments be allowed to become fully invaded before control operations were started, then the costs would rise to US$ 86.5, 20.5, 278.0 and 11.1 million, respectively. The impacts and costs are significant and are comparable with those calculated independently for other South African catchments. Water is acknowledged to be a key constraint to economic growth in South Africa and there is considerable pressure for efficient and sustainable use of the limited water resources. The projected impacts would justify control programmes aimed at clearing alien invaders for water conservation. #

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Section: Other Benefitsmentioning

confidence: 99%

Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management

Maitre¹,

Wilgen²,

Gelderblom³

et al. 2002

Forest Ecology and Management

239

136

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“…Le Maitre, personal observation). In addition, alien invasive plants typically suppress ground-cover and understorey vegetation and the absence of these shallow root systems increases the likelihood of soil loss after a fire (Scott et al, 1998).…”

Section: • Horizontal and Vertical Continuity Acacia Cyclops Andmentioning

confidence: 99%

“…Scott, Versfeld and Lesch, 1998 Drakensberg, KwaZulu-Natal Pinus patula 37 t/ha of soil was lost following fires in pine stands compared to 1.8 t/ha in adjacent grassland. The degree of damage to the soil following fires was in proportion to the degree of invasion, with heavily-invaded sites being the worst affected.…”

Section: Impact Sourcesmentioning

confidence: 99%

Impacts of invasive alien plants on water quality, with particular emphasis on South Africa

Chamier¹,

Schachtschneider²,

Maitre³

et al. 2012

WSA

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We review the current state of knowledge of quantified impacts of invasive alien plants on water quality, with a focus on South Africa. In South Africa, over 200 introduced plant species are regarded as invasive. Many of these species are particularly prominent in riparian ecosystems and their spread results in native species loss, increased biomass and fire intensity and consequent erosion, as well as decreased river flows. Research on the impact of invasive alien plants on water resources has historically focused on water quantity. However, although invasive alien plants also affect the quality of water, this aspect has not been well documented. Alien invasive plants increase evaporation rates, and reduce stream flow and dilution capacity. The biomass inputs of alien invasive plants, especially nitrogen fixers such as Acacia spp., alter nutrient cycles and can elevate nutrient concentrations in groundwater. Alien plant invasions alter the fire regimes in invaded areas by changing the size, distribution and plant chemistry of the biomass. More intense fires increase soil erosion and thereby decrease water quality. In contrast to riparian invasions, aquatic invasive plants have been more extensively studied in South Africa and their impacts on water quality have been relatively well monitored. Water quality in South Africa is rapidly deteriorating, and all factors that influence this deterioration need to be taken into account when formulating actions to address the problem. The changes in water quality brought about by alien plant invasions can exacerbate the already serious water quality problems.

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“…Physical damage to the soil can occur, resulting in increased erosion after fire. For example, 6 tonnes of soil per hectare was lost following fires in pine stands compared to 0.1 tonnes per hectare following fire in adjacent fynbos in the Western Cape (Scott et al 1998 Finally, there is evidence from the Cape Peninsula (and elsewhere in fynbos ecosystems) that ecosystem diversity can be restored after invasive alien plant control operations, especially in areas that were not too heavily invaded or have not been invaded for so long that the soil-stored seed banks have become substantially depleted (Holmes and Richardson 1999). Managers have typically relied largely on the unaided recovery of native species from residual individuals or seed banks to drive restoration (Vosse et al 2008), but areas that have been densely invaded for long periods could require further interventions in the form of reintroductions of certain major plant guilds (groups of plants with similar response strategies for dealing with disturbance) to ensure that the original guild structure of the vegetation could be restored (Holmes and Richardson 1999).…”

Section: Opposing Views Of Alien Plant Controlmentioning

confidence: 99%

“…The risk of erosion is therefore relatively short-lived, and needs to be assessed against the risks associated with not clearing the plantations. There is a risk that the plantations could burn in a wildfire, which will also lead to erosion (Scott et al 1998). In addition, and more importantly, leaving the plantations in place will provide an ongoing source of seeds that will invade adjacent natural vegetation, perpetuating the problem of invasive alien plant control, and leading to more widespread risks of erosion over larger areas (van Wilgen and Scott 2001).…”

Section: Concerns Regarding the Negative Impacts Of Controlmentioning

confidence: 99%

Evidence, Perceptions, and Trade-offs Associated with Invasive Alien Plant Control in the Table Mountain National Park, South Africa

Wilgen¹

2012

E&S

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ABSTRACT. The Table Mountain National Park is a 265 km 2 protected area embedded within a city of 3.5 million people. The park contains an extremely diverse flora with many endemic species, and has been granted World Heritage Site status in recognition of this unique biodiversity. Invasive alien plants are arguably the most significant threat to the conservation of this biodiversity, and the past decade has seen the implementation of aggressive programs aimed at the removal of invasions by these plants. These invasive alien plants include several species of trees, notably pines (Pinus species) and eucalypts (Eucalyptus species), which historically have been grown in plantations, and which are utilized for recreation by the city's residents. In addition, many citizens regard the trees as attractive and ecologically beneficial, and for these reasons the alien plant control programs have been controversial. I briefly outline the legal obligations to deal with invasive alien plants, the history of control operations and the scientific rationale for their implementation, and the concerns that have been raised about the operations. Evidence in support of control includes the aggressive invasive nature of many species, and the fact that they displace native biodiversity (often irreversibly) and have negative impacts on hydrology, fire intensity, and soil stability. Those against control cite aesthetic concerns, the value of pine plantations for recreation, the (perceived) unattractive nature of the treeless natural vegetation, and the (incorrect) belief that trees bring additional rainfall. The debate has been conducted through the press, and examples of perceptions and official responses are given. Despite opposition, the policy promoting alien plant removal has remained in place, and considerable progress has been made towards clearing pine plantations and invasive populations. This conservation success story owes much to political support, arising largely from job creation, and a strong body of scientific evidence that could be cited in support of the program.

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Erosion and Sediment Yield in Relation to Afforestation and Fire in the Mountains of the Western Cape Province, South Africa

Cited by 80 publications

References 18 publications

Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management

Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management

Impacts of invasive alien plants on water quality, with particular emphasis on South Africa

Evidence, Perceptions, and Trade-offs Associated with Invasive Alien Plant Control in the Table Mountain National Park, South Africa

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