Increasingly we are seeing the terms ‘ecosystem services’, ‘ecosystem functioning’ and ‘ecosystem processes’ in the media and the scientific literature, to highlight the benefits the natural environment provides to our wellbeing. Invasive species, from bivalves to balsams, have the potential to impact on ecosystem services, though it is widely accepted that there are gaps in our understanding within this field.
Ecosystem services can be defined as the ecosystem processes that we as humans benefit from and they can be categorised into four groups:
Provisioning: The ecosystem provides products essential for our everyday needs including timber, fuel, food, genetic resources and medicine.
Regulating: We gain from natural services including pollination of wild plants and crops by bees, by rivers and floodplains providing natural flood management, and climatic regulation.
Cultural: We benefit from natural spaces for recreation and social activity. We find harmony in natural areas that are aesthetically pleasing.
Supporting: These services underpin all of those mentioned above. Biological diversity promotes stability and a healthy ecosystem, nutrient acquisition and flow through the ecosystem by fungal and invertebrate decomposers, and primary production.
In November 2011, I attended the 2nd World Conference on Biological Invasions and Ecosystem Functioning in Argentina. The conference brought together over 300 invasive species scientists from more than 20 countries and included talks on invasive species impacts in the broadest sense. For me, what was interesting was that the conference covered the impact of invasive species on every category of ecosystem services. A number of talks and posters focused on the impact of invasives species on provisioning services including a case study of the north American beaver in Chile that is having a catastrophic impact on the sub-Antarctic forests by changing the structure and amount of energy within. In Patagonian rivers, invasion by a microscopic diatom has led to significant shifts in the biogeochemical composition of the water body which may affect the nutrient flow through the system. In the southern states of the US, Tamarix species are severely affecting the water conservation of the region with an annual cost of water loss and flow changes estimated to be between $133-265 million.
The value of native pollinators as a regulating service to the UK economy has been estimated at £1.5 billion per year. Not only threatened by habitat change, bee populations in the UK have been decimated by non-native fungal species, viruses and may soon face a new threat from the Asian hornet which is expected to reach the UK from mainland Europe anytime soon. Indirectly, the pollination network is threatened by non-native plant species. Himalayan balsam, with its high sugar nectar production (higher than any other native European species) lures pollinators away from native species thus reducing genetic diversity in native plant populations.
A couple of presentations at the Biolief conference highlighted the impacts of non-native mammals on cultural services, where feral pigs, boars and mink were shown to degrade protected areas in Argentina, rich in aesthetic value. Closer to home, here in the UK, the invasion of Japanese knotweed has threatened the aesthetic value of a historic Cornish mine, recently designated as a World Heritage Site by growing in, around and over the remaining buildings. Invasive species also affect recreational activities, as in the case of Himalayan balsam, which reduces access to rivers for fishing and boating activities. The aquatic weed species, floating pennywort can impede boating activities along rivers and the recently published report on the economic impacts of invasive non-native species in Great Britain estimate the cost to recreation by this south American species to be over £25 million per year. Even in highly managed amenities we are not free from the costs and problems associated with invasive species. In the United States, the costs of weeds in golf courses are in excess of $1 billion a year.
The health of our soils is fundamental as a supporting service. Soil provides native plant species with essential resources, which in turn promote the biological diversity of invertebrate organisms and fungi. These provide ecosystem services such as conservation and fertility, which boost the productivity of agricultural systems and increase the abundance of beneficial organisms to control pest species naturally. In the UK, it is estimated that 2.2 million tonnes of top soil is eroded each year, costing the economy between £150-250 million. Invasive plant species can increase the risk of erosion by outcompeting native plant species that provide bank stability along our river systems. Invasive fauna can also impact supporting services; it is estimated that the cost of the non-native New Zealand Flatworm to Scottish agriculture may be in excess of £16 million per year. These ferocious predators of native earthworms have a geographic distribution of over 90% of Scotland’s land area.
The Millennium Ecosystem Assessment Toolkit provides a tool to evaluate and prioritise groups of invasive species that may affect specific ecosystem services. The practice of costing nature has its benefits in preserving natural ecosystems and should not be seen simply as putting a price-tag on the ‘commodity’ for the benefit of mankind. As in the conservation of keystone species, if we regard ourselves as those, we must manage and conserve the environment and those influences which degrade it to ensure we are provided with a sustainable, functional ecosystem long into the future.
Dr. Rob Tanner
Senior Scientist, Invasive Species Management, CABI
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