Although the costs and manpower involved in control of INNS can often be substantial, the cost of widespread impacts of INNS on biodiversity is likely to be many times higher because many impacts are indirect, non-market costs. The economic impact of the displacement of a species, or a change to ecosystem functioning is very difficult to value and some changes to ecosystems may go unnoticed, especially if an established non-native species is not considered a nuisance yet. The impact of INNS on biodiversity, like the cost of control, increases with the time a species has been present in the country as shown in the case studies.
An indirect effect of INNS can be a perceived devaluation of the natural environment when INNS are present. The resources spent on control of these INNS are driven by people’s fear of losing an attractive or rare species. Hence, the resources that are invested in the eradication of INNS from natural habitats in Great Britain and in the protection of a few, high profile endangered species, such as the red squirrel, illustrate some of the appreciation of native flora and fauna and the willingness to protect them. However, very little data are available that attributes a monetary value on the existence of the native flora and fauna separately from the control costs to protect them. One example that was available was that of the impact of the American mink on water vole.
There is a strong causal link between the introduction and spread of mink and the decline in water vole population in Britain. The entire population of water vole would crash if mink control measures failed, regardless of other conservation or land management effort (Jonathan Reynolds, Game and Wildlife Conservation Trust, pers. comm.). The value of water vole was estimated using a contingent valuation telephone survey giving a willingness
to pay value of £7.44 in 1996, £10.46 today (White et al. 1997). Therefore, with a total population loss of 1,946,000 water voles between 1990 and 1998, a cost of £2,544,395 can be attributed to mink. Although the water vole population has been stable in recent years, the reduction in population of water vole is still a cost to the economy, as people are not able to gain enjoyment from the water vole that no longer exist. This is included as an annual cost in the same manner as the lost production experienced by crofters in the Western Isles is included as an annual cost. In the Western Isles the presence of mink prevents crofters from keeping poultry, and here the presence of mink prevents the water vole population from re-establishing itself, and is therefore considered to be an annual cost. This cost may reduce if the water vole population increases in the future and the value that people place on a water vole reduces as they become more common. It is, however, a current annual cost.
Table 14.3. Cost of biodiversity loss due to mink.
Pop. 1990 Pop. 1998 Pop. decrease Cost at £10.46 per vole
England 1,479,795 227,760 156,504 £1,637,036
Scotland 740,488 113,971 78,315 £819,171
Wales 79,718 12,270 8,431 £88,188
GB 2,300,000 354,000 243,250 £2,544,395
The responses to the questionnaire from people who indicated that they work in the biodiversity and conservation sector indicated that 26 INNS species caused a quantifiable reduction in biodiversity (Fig. 14.1). Himalayan balsam was mentioned 12 times, but the majority of species were mentioned only once or twice. The respondents were asked to indicate the biodiversity costs of the species they mentioned in nine classes, ranging from £1 to “more than £500,000”. However, many respondents indicated that the value of reduction in biodiversity was almost impossible to estimate, and therefore the response they had given was a guess, or they were not prepared to provide an estimate at all. Of the responses provided, it is clear that the estimates of lost biodiversity value vary considerably, confirming the difficulties in estimating the value of lost biodiversity. However, all these respondents were controlling INNS for the primary purpose of protecting native biodiversity, so even though they could not put a monetary value on the biodiversity lost due to the INNS, they knew that the native biodiversity has a value that was worth protecting.
Figure 14.1. The number of times that INNS were identified as causing a reduction in biodiversity. Other includes responses where no species were identified.
The indirect costs to biodiversity are undoubtedly very high, but due to the lack of information on which to base an estimate, no attempt to put a value on indirect costs of INNS to biodiversity specifically has been made. This is due to a paucity of studies that have investigated the cost of reduced biodiversity in terms of its intrinsic value, or the ecosystem services provided. In the descriptions of the costs of INNS to various sectors described in this report, it has become clear that the loss of species as a result of INNS can or could be very expensive to the economy and if an ecosystem services approach were applied to the impact and cost of every INNS, then it is likely that the costs attributable to this sector would be much higher than that recorded here.
Table 14.4 Biodiversity costs by country
England Scotland Wales GB
Direct Costs £9,650,000 £5,293,000 £5,709,000 £20,652,000
Research £17,387,000
Quantifiable indirect costs
£1,526,000 £509,000 £509,000 £2,544,000
Total £11,176,000 £5,802,000 £6,218,000 £40,583,000
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