Floating Pennywort (Hydrocotyle ranunculoides)

Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 45-50)

Floating pennywort was introduced into Britain from North America in the 1980s through the aquatic plant trade (Kelly 2006). There are over 150 known sites of infestation in England and Wales, although none are known in Scotland. Floating pennywort is found in slow-flowing water such as ditches, lowland rivers and on the edges of lakes, where it forms dense vegetative mats that out-compete most native aquatic plants. The species can negatively impact upon fish through restricting access to feeding and resting spaces and can contribute to localised flooding through the blocking of drainage systems. Floating pennywort has a rapid growth rate of up to 20 cm a day and is particularly difficult to control due to this rapid vegetative growth.

4.3.1 Control Cos ts

Dr Jonathan Newman (pers. comm.) has stated that floating pennywort is the most expensive of all aquatic weeds to control in the UK at the moment, with a cost of

£1800-£2000 per km for removal. The Environment Agency (EA) estimate they have spent

£510,260 on control of approximately 300 km of floating pennywort in 2009 (T Renals pers.

comm.). British Waterways spend £50,000, primarily on two separate river navigations. In addition, many other bodies are known to be involved in control of this species. Ryland (2008) stated that in Pevensey Levels SSSI, Natural England pays farmers to remove floating pennywort from ditches at a rate of £2.90m-1 under a higher level stewardship scheme. The cost of control at that site, where about 10% of the ditches are infested (45 km), was approximately £35,000 p.a. in 2008. The range of floating pennywort is expanding and it is assumed that the cost doubled to £70,000 in that area in 2009 despite control efforts. Ryland (2008) estimated that the cost of implementing a localised control strategy at Pevensey Levels would be £150,000 per annum for the first five years. There are many

other sites where floating pennywort is being managed, such as a small eradication programme in Gillingham costing £8,400 (Kelly 2006) and an infestation in Reading recently cost £20,000 to deal with5, excluding the removal of material. The total known spending on control of floating pennywort is therefore £658,660. This does not include costs incurred by Internal Drainage Boards and private owners of lakes, fisheries and watercourses. The most recent estimate for the whole country for the control, management and disposal of H.

ranunculoides was £1.93 million in 2008 (Newman, quoted in EPPO 2010). In 6 years, these costs had increased 7 fold.

4.3.2 Cos ts to Le is ure a nd Re cre a tion

Any shallow, slow-moving waterway that is infested with floating pennywort will rapidly become non-navigable and useless for fishing. This would certainly have been the case for much of the 400 km subject to control efforts above. We have assumed that floating pennywort is indiscriminate in its colonisation of the 400 km of waterways cleared this year and that 50% of these water bodies are used for recreation, the rest being drainage ditches etc., which are not used for recreational purposes. Floating pennywort is most prolific in lowland eutrophic water bodies, which tend to be mostly associated with larger conurbations.

These watercourses would also tend to have the greatest angling, navigation and recreational use.

The British Waterways Inland Waterways Surveys provides useful data that can be used to extrapolate the recreational value of canals and rivers through the country. Their latest survey, British Waterways (2008) stated that in 2008, 3.4 million adults visited one of their waterways across their 3,540 km network in an average two-week period. This is equivalent to 2087 visitors per km per month. Therefore, on the basis that 200 km of canals are infested (see above) for a two month period this affects 834,300 visitors, of which an estimated 10% are anglers, a further 10% use the sites in other ways and the remaining 80% are general visitors.

A 1999 investigation of the benefits to anglers and other recreation users (e.g. swimming, wildlife viewing) of increasing flow rates of low-flow rivers in England gave a mean willingness to pay (WTP) value of £68.03 per year for anglers for improved fishing, brought about by low-flow alleviation. Mean WTP for other on-site recreational users was £28.22 per year and for general users the mean WTP ranged between £5.34 and £10.78 per year for an

environmentally acceptable flow regime (Willis and Garrod 1999). These values related to low-flow alleviation, whereas the presence of floating pennywort would result in a complete loss of fishing. However, given the similarities in the effects of low-flow and pennywort infestation on rivers, it is assumed that the same willingness to pay values are applicable at current levels, providing values in today’s prices of £88.36, £36.65 and £10.47 (using the average of the WTP of general users).

It was assumed that the negative impacts of floating pennywort are felt for a two-month period, during which there is sufficient vegetative growth to cause a problem and the control measures are being undertaken and the vegetation removed. Therefore, based on these visitor numbers above and the willingness to pay figures provided, the presence of floating pennywort costs an estimated £17,428,120 per year during the period in which its presence is a significant issue.

Floating pennywort will also cause a problem to boat users in areas of significant growth.

British Waterways currently spend £50,000 on floating pennywort control, which, at an average spend of £2000 per kilometre, suggests that only 25 km of canals are infested to an extent that impedes boating. We assume that this represents at least five stretches of floating pennywort, each of which has an impact on at least five times the length of waterway that was infested. Therefore, an estimated 125 km of the canal network would not be used for boating as a result of the presence of floating pennywort. Annual tourism spending related to leisure boating has been estimated at £1.8 to £2.2 billion6. This gives a value of

£22,553 per kilometre of river and canal and if, as above, it is assumed that the impact is felt for a two-month period, then the loss to tourism through the effects of floating pennywort on boating on canals can be estimated at £469,849. In addition, boating on rivers can also become restricted by floating pennywort (T. Renals, pers. comm.) and therefore, of the 300 km of floating pennywort controlled by the Environment Agency on rivers in England and Wales it is assumed that 50 km affects boating. Based on the same assumptions used to calculate the effect on boating on canals (each affected area is 5 km long, affecting five times that length i.e. 25 km, with 10 stretches of floating pennywort affecting boating) a total of 250 km of river will be affected by the presence of floating pennywort. At the same value of £22,553 per kilometre of river costs to boating on rivers in England and Wales can be estimated at £5,638,250, giving a total of £6,108,099.

6 http://www.britishmarine.co.uk/upload_pub/Ec_Bens_Exec_summary.pdf

4.3.3 Tota l cos ts

Current costs of floating pennywort in terms of management and the effect on tourism are as follows:

Table 4.8. Total annual costs of floating pennywort.

England Scotland Wales GB

Management £1,815,000 - £115,000 £1,930,000

Recreation £23,468,000 - £69,000 £23,537,000

Total £25,283,000 - £184,000 £25,467,000

The ratio of the known management costs between England and Wales has been used to proportion the recreational costs between the two countries. No costs have been attributed to Scotland as no infestations of floating pennywort have been recorded there.

It is likely that floating pennywort will lead to additional flooding, both through flooding previously unaffected areas, or exacerbating flooding that is already occurring. This will have an associated economic cost. However, it is not possible to estimate this at present as no data are available to indicate where these additional flood events may take place. If they occur primarily on agricultural land, through the blocking of drainage ditches, then there may be costs due to loss crops, or lost grazing. Alternatively if the ditches or streams affected are located in built up and urban areas, then floating pennywort blocking these streams may cause houses to flood. This would again have an economic cost that could be considerable.

However, no data were available to establish whether additional flooding had taken place due to the presence of floating pennywort, and if it had, whether it should be considered to be a one-off event or contribute to the annual cost of this species.


British Waterways (2008). British Waterways Annual Inland Waterway Visitor Survey.

Quoted in A vision for 2020. British Waterways. 14pp.

http://www.britishwaterways.co.uk/media/documents/BW_2020_A_Vision_for_the_Fut ure.pdf

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5 Agriculture and Horticulture

As mankind’s staple industry worldwide, agriculture has been instrumental in the rise of civilisations and society through domestication of livestock and crops to supply sufficient, affordable food to feed its populations. In Great Britain, a small, densely populated island, agriculture today is intensive and highly mechanised and produces about 60% of the nation’s food needs7. Society and national economies hold little tolerance for the adverse impacts of native or non-native pests and diseases on yield and quality. This is also true in the horticultural and gardening sector, with a retail turnover of over £5 billion8.

The INNS affecting agricultural and horticultural industries in England, Wales and Scotland are diverse and represented by mammal, bird, insect, mollusc and plant taxa as well as fungi, bacteria and viruses. Disturbance is widely recognised as one of the key drivers of biological invasions (Mack et al. 2000), as discussed earlier, and arable fields are by their nature highly disturbed environments, presenting numerous opportunities for invasion by both native and non-native species.

Around 18.7 million ha of the UK are classified as agricultural land (Nix 2009), approximately 67% of the land area in Great Britain9, and despite the rise of many organic farms, the repeated use of pesticides is still intrinsic in managing the threat of damage and reduced yield, ensuring ease of harvesting, preventing long-term weed build up and vectoring of pests and diseases.

Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 45-50)