Impacts on the environment
A biodiverse environment underpins the survival of those people living in poverty around the world, many of whom have no alternatives to the products they take from the land, forests, rivers and oceans. They are therefore extremely vulnerable when biodiversity is reduced.
Invasive species can decomate a country's native species by attacking or outcompeting them for nutrients, water, space and breeding sites. The availability and quality of natural resources are diminished as a result.
Invasive plants can come to dominate pastures and crop fields – particularly if they have allelopathic properties, which means they release chemicals that suppress the growth of other nearby plants. The increased cost of land preparation and maintenance this leads to is a serious concern for farmers. Invasive plants can also modify nutrient availability, by affecting soil pH for example, and cause land degradation and erosion.
A loss in the biodiversity of agro-ecosystems also undermines populations of the ‘natural enemies’ that keep native pests under control, causing problems for farmers who do not have access to insecticides or other means to manage them.
Dense growths of invasive plants can increase the frequency of wildfires, with some species also containing highly flammable compounds.
Reducing forest biodiversity
Invasive plants are having a number of impacts on forests and the valuable resources they provide, with detrimental effects on the communities that rely on them. They inhibit regeneration of native herbaceous species, including important medicinal herbs and shrubs, and contribute to reduced diversity.
In rivers, lakes, streams and reservoirs, aquatic weeds can impact on the ecology by displacing native species, including fish. Few native plants can grow under the canopy created by Mimosa, for instance. Infestations can also interfere with irrigation, degrade the habitat and trap sediment – decreasing water supply and promoting flooding.
The heavy use of chemical pesticides, insecticides and herbicides to control invasive pests has in itself had detrimental consequences to ecosystems across the world, leading to pollution of soil and water, as well as causing harm to plants, animals and people working in the fields.
Trees and shrubs that have deep roots or a higher water requirement than indigenous species – such as pine trees, which were introduced into southern hemisphere countries for forestry purposes – have a dramatic effect on hydrology. Just a minor reduction in the availability of water can be catastrophic in areas where it is already scarce, or which are subject to persistent droughts.