Invasive plants and fire: A threat to biodiversity
21 July 2017
With the fire season still upon us, Invasive Plants continue to pose a threat to the environment and infrastructure. Invasive plants can burn with 10 times the heat of indigenous plants, destroying the fynbos seeds stored in the soil, or adapted for release in low-heat fires.
The invasive plants’ own seeds survive, however, and as a result they usually sprout thicker than before on land that has recently burnt. An increase in invasive plants is a cause for concern as they increase fuel loads and aggravate the intensity and heat of fires, making it more difficult and unsafe to control. This type of vegetation also makes fires extremely hot, which damages the burnt area’s soil structure and that has a negative impact on the productivity of such soil.
The effect of invasive vegetation on fire increases the intensity of the flames, having an impact on indigenous vegetation, and increasing the likelihood of extreme or catastrophic loss to infrastructure and/or lives. Invasive plants out compete most endemic and indigenous plants, which require fire to germinate, thus multiple fires over a short period leads to loss of species and biodiversity.
Invasive plants also increase the fuel load, as fynbos composition is naturally of small to medium high shrubs, with very few tree species. Erosion occurs due to the adventitious root system of the invasive plants. A veldfire thus removes the vegetation holding the topsoil in place and the soil is loosened and is lost with the next rainfall.
Priority areas to consider first when clearing are those around buildings if there is a risk of fire. Other areas include low-density infestations, to keep the spread of invasive plants into the surrounding areas in check, the sites where initial control work has been completed and regrowth is present, to prevent densification and further infestation. Disturbed sites, to prevent new infestations from mass germination of alien seeds in the soil. Seedlings should be controlled while they are less than 0.5 meters tall to avoid costly control work later.
Everyone is impacted directly or indirectly by invasive species – which means that there’s a shared responsibility to manage the problem. Landowners on which a listed invasive species occurs must notify any relevant competent authority, in writing, of the listed invasive species occurring on that land and they must take steps to control and eradicate the listed invasive species and to prevent it from spreading. For properties over one hectare, a Control Plan for listed invasive species must be developed. Applications must be done for a permit to keep Category 2 invasive plants and adhere to permitting conditions for Category 2 plants. Finally control methods must be appropriate for the listed species and the environment.
Failure to do so can result in a fine and/or the work being done by the authorities, at the expense and risk of the land-owner. This includes any necessary follow-up clearing of the invasive plants, and any fire-related need to deal with the cleared biomass.
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