Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 183-192)

These case studies illustrate how costs caused by INNS increase depending on the stage of invasion that the species has reached (see Table 16.1). In situations where the species is in an early stage of invasion, the costs of eradication are relatively low. This is illustrated by

the Asian long-horned beetle, water primrose and carpet sea squirt. The costs of keeping a species out of Great Britain, or ensuring that any outbreaks are immediately eradicated are very low in comparison to the costs incurred in other countries where the species are fully established. The costs incurred in Great Britain for these species are mainly due to prevention and quarantine measures and localized eradications.

Table 16.1. Cost of intervention controls by species.

Species Control Stage Cost

Asian long-horned beetle

Anoplophora glabripennis

Early stage eradication £34,000 Late stage eradication £1,316,416,000 Carpet sea


Didemnum vexillum

Early stage eradication £2,356,000 Late stage eradication £927,608,000 Water primrose Ludwigia spp. Early stage eradication £73,000 Late stage eradication £241,908,000 Grey squirrel Sciurus


Early stage eradication £440,000 Late stage eradication £850,734,000

Coypu Myocastor


Mid stage eradication £4,700,000 Late stage eradication £18,800,000

However, when species become established and consolidate their presence in the country, the eradication costs increase considerably. All the case studies illustrate that the cost of late stage eradication vastly exceed eradication at an early stage of invasiveness. For example, the cost of eradicating water primrose at its present stage of invasiveness is less than 0.03%

of its potential eradication costs if the species is allowed to become fully established.

Figure 16.1. Average estimated eradication costs, depending on stage of invasiveness.

Prevention costs are on an annual basis, other costs are total.

Generally speaking, the costs increase exponentially if species are allowed to spread (Fig.

16.1). These case studies therefore show that early eradication is more cost-effective than long-term control or eradication of well-established INNS. They also demonstrate that even eradication of some well-established INNS could be more cost-effective that long-term control of the species as annual costs can quickly exceed eradication costs over a few years. These conclusions are in agreement with findings based on the other species and the general consensus on the best methods to deal with biological invasions (Wittenberg and Cock 2001). They are also supported by the fact that most attempts to eradicate well-established INNS have failed (Pimentel et al. 2001), emphasising that eradication at an early stage of invasion is the most cost-effective method of controlling an INNS.

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17 Discussion

The total annual cost of INNS to the British economy, as estimated in this report, is

£1,678,434,000. Table 17.1 presents the costs by sector and country and reveals that the costs to the sectors are widespread and often significant. In most cases, the only costs that could be quantified are the direct market costs, such as the money spent on control measures or the reduction in productivity due to the presence of an INNS. Indirect costs constitute less than 1% of our total estimate and exclusion of the indirect costs from the estimate for better comparison with other studies reduces the estimate of the total cost to


Table 17.1 Estimated total costs of INNS to Great Britain by sector and country.

All Costs England Scotland Wales GB

Agriculture £839,189,000 £156,120,000 £71,110,000 £1,066,419,000 Forestry £45,780,000 £48,666,000 £14,950,000 £109,396,000 Quarantine and


£14,523,000 £1,287,000 £1,956,000 £17,766,000 Aquaculture £4,370,000 £722,000 £2,053,000 £7,145,000 Tourism and


£78,920,000 £13,059,000 £5,759,000 £97,738,000 Construction,

Development, Infrastructure

£194,420,000 £6,870,000 £11,078,000 £212,368,000

Transport £62,894,000 £9,621,000 £8,768,000 £81,283,000 Utilities £8,515,000 £1,119,000 £483,000 £10,117,000

Research £17,387,000

Biodiversity and Conservation

£11,176,000 £5,802,000 £6,218,000 £40,583,000 Human Health


£37,844,000 £4,470,000 £5,816,000 £48,130,000 Subtotal £1,297,631,000 £247,736,000 £128,191,000 £1,708,332,000 Double count


£6,170,000 £3,268,000 £3,073,000 £29,898,000 Total costs


£1,291,461,000 £244,468,000 £125,118,000 £1,678,434,000

a The total cost for biodiversity does not equal the country totals, due to the inclusion of research costs, which are not divided by country. Similarly, the GB total does not equal the country totals.

B The double counting, removed to obtain the overall total cost estimate, relates to the £1,945,000 cost of quarantine and surveillance for forestry species that is included in the quarantine, forestry, and research sectors.

The £8,621,000 cost of rhododendron control is included in both the forestry and biodiversity sectors. Finally, the entire cost of research is included in the biodiversity and conservation sector, as all research carried out on INNS will be of benefit to biodiversity and conservation either directly or indirectly.

INNS have by far the largest effect on the agriculture and horticulture sector, amounting to just under two thirds of the total estimated cost (Table 17.1). These costs arise from a wide variety of species, from plant pathogens, insect pests and weeds to some of the most common mammalian species in Great Britain, such as rabbit. A further cost that can be considered to affect agriculture is the amount spent on quarantine and surveillance. While approximately £1.9 million of a total of approximately £18 million is spent on forestry quarantine, the remaining £16 million is spent on quarantine and surveillance measures for plant health, primarily agriculture. This emphasises the impact of INNS on the agricultural industry in Britain. The cost to construction, development and infrastructure is also considerable, but the costs in this sector arise from very few species, with Japanese knotweed being by far the most costly species, followed by the brown rat.

The majority of the costs are incurred by England, with far lower costs to Scotland and Wales. Based on the respective land areas, England has higher and Scotland lower costs than expected, and Wales roughly what one would expect if the costs were equally distributed over Great Britain. This is due to a number of factors. England has proportionally more agricultural land than Scotland and Wales and as this is the sector with the highest costs, a larger proportion of the costs are incurred in England. England also has more international transport links than the other two countries and is therefore more likely to be the entry point for any invasion. Consequently, more non-native species have become established in England and some species that are widespread in England only have a limited distribution in Scotland and Wales (e.g. grey squirrel).

Of those costs that could be directly attributed to a species or group of species, plants as a group inflict the highest costs to the economy, with mammals and plant pathogens also causing considerable costs across the sectors (Table 17.2). This is likely to be due to the large number of non-native plants in the country, compared to the number of non-native species in other taxa. Spending on INNS management in general, for example by conservation organisations on general land management where a portion of the cost relates to INNS, was not included in this summary table.

On an individual species level, rabbits and Japanese knotweed cause the highest cost (Table 17.3), reflecting their widespread distribution throughout the country, as well as their impact on a number of different sectors.

Table 17.2. The annual costs of species groups to the British economy.

Group Cost

Plants £483,030,000

Plant pathogens £403,063,000

Mammals £402,483,000

Insects £254,695,000

Birds £6,284,000

Total £1,563,127,000

Table 17.3. The annual cost of individual species or species groups to the British economy.

Species Cost

Rabbit £263,173,000

Japanese knotweed £165,609,000 Common field-speedwell/

wild oat


Rat £62,162,000

Potato cyst nematodes £50,000,000 Non-native deer £34,907,000

Varroa mite £27,119,000

Floating pennywort £25,467,000

House Mouse £17,876,000

Grey squirrel £14,067,000

Rhododendron £8,621,000

Slipper limpet £5,514,000

Mink £4,797,000

Geese/swans £3,617,000

Green spruce aphid £3,569,000

Signal crayfish £2,689,000

Giant hogweed £2,362,000

Himalayan balsam £1,000,000

Buddleia £961,000

Edible dormouse £364,000

Great spruce bark beetle £163,000

Carpet sea squirt £107,000

Parakeets £38,000

Total £794,182,000

The difference in the estimated costs of species and species groups (Tables 17.2 and 17.3) reflects that the calculations for the cost of INNS to agriculture and due to plant pathogens are based on the treatment of all unwanted species in agricultural systems, and the portion of these species that are estimated to be non-native, and not on the treatment of individual species. Consequently, it can be seen that roughly one third of the total cost estimate is based on the more detailed calculations of the impact of individual species.

The results from this study demonstrate that the highest level of interest from stakeholders, both on a sector and a species level, is not necessarily in areas where INNS cause the most costs. The majority of respondents to the questionnaire worked in the biodiversity and conservation sector, even though costs were much higher in other sectors. Follow-up interviews with respondents from the biodiversity and conservation sector confirmed that, although people in this sector are mostly aware of the ecological impact, they were unable to put a monetary value on the damage or changes due to INNS. Oreska and Aldridge (2010) reported similar difficulties associated with the valuation of impact of INNS to ecosystems by stakeholders. This does not mean, however, that the costs of INNS are inconsiderable in this sector. Indeed, the true costs are likely to be higher than indicated in this report and the low cost estimate is due to the difficulties in placing a monetary value on the effects of INNS on the environment and ecosystems. This research has also revealed that the cost of control or perceived impact of INNS as a separate group is limited in various sectors, because all undesirable species are treated in the same manner, whether the species is native or non-native to Great Britain (e.g. insect pests in agriculture or hull-fouling). However, it was clear from interviews with people in those sectors that the lack of specific treatment is not due to a lack of awareness of the problems caused by INNS. For example, strict regulations exist in the shipping industry to prevent the introduction and spread of non-native species.

Furthermore, there is considerable spending on quarantine and surveillance, again indicating awareness of the problems caused by INNS, as both quarantine and surveillance measures help to prevent the introduction, establishment and spread of new non-native species.

Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 183-192)