Public value at risk from Phytophthora ramorum and Phytophthora kernoviae spread in England and Wales

Journal of Environmental Management 191 (2017) 136e144

Contents lists available at ScienceDirect

Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman

Research article

Public value at risk from Phytophthora ramorum and Phytophthora kernoviae spread in England and Wales Ben Drake a, *, Glyn Jones b a b

RSK ADAS Ltd, 4205, Park Approach, Thorpe Park, Leeds, LS15 8GB, United Kingdom FERA Science Ltd, Sand Hutton, York, YO41 1LZ, United Kingdom

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 August 2016 Received in revised form 1 January 2017 Accepted 6 January 2017 Available online 13 January 2017

Heritage gardens, heathland and woodland are increasingly under threat from the non-native tree and plant diseases Phytophthora ramorum and Phytophthora kernoviae. However, there exist only limited literature that estimates the public non-market value that may be lost from a continued spread of Phytophthora ramorum and Phytophthora kernoviae into these habitats. This paper therefore uses a contingent valuation survey to assess the non-extractive public use and non-use values at risk from an uncontrolled spread of these diseases in England and Wales. Results estimate that £1.446bn of public value is at risk in England and Wales per year from an uncontrolled spread of Phytophthora ramorum and Phytophthora kernoviae. The greatest public value at risk, of £578 m/year, is from an uncontrolled spread of these diseases to heritage gardens, while the lowest public value at risk, of £386 m/year, is from disease spread to heathland. The findings of this paper should help policymakers make informed decisions as to the public resources to dedicate towards Phytophthora ramorum and Phytophthora kernoviae control in England and Wales. In this regard, the current control programme to contain these diseases appears cost-effective in light of the public value at risk estimates produced by this paper. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Tree disease Contingent valuation Willingness to pay Heritage gardens Ecosystem services

1. Introduction Native trees and plants are now under threat on a global scale from invasive pathogens (Potter et al., 2011). Recently, there has been an acceleration in the occurrence of non-native harmful pests and pathogens in the USA, Europe and the UK (Boyd et al., 2013). Growing international trade may be responsible for some of this proliferation, with Santini et al. (2013) finding that trade has assisted at least 68% of harmful and invasive forest pathogens that have been introduced into Europe. The mobility of these pathogens across international borders is not without economic consequences. For instance, in the USA, it is estimated that alien-invasive pathogens cause US$23.1bn of damage to crop and forest products every year (Pimentel et al., 2005), while in New Zealand it is estimated the pathogen Dothistroma septosporum (D. septosporum) costs the forest industry NZ$19.8 m every year in terms of reduced yield and control costs (Watt et al., 2011). Economic consequences of forest pathogens are also felt in the property sector where the spread of Phytophthora ramorum (P. ramorum) is expected to reduce

* Corresponding author. E-mail address: [email protected] (B. Drake). http://dx.doi.org/10.1016/j.jenvman.2017.01.013 0301-4797/© 2017 Elsevier Ltd. All rights reserved.

the value of single family homes in California, USA, by US$135 m over the period 2010e2020 (Kovacs et al., 2011). In the UK, P. ramorum and Phytophthora kernoviae (P. kernoviae) are non-native diseases that were introduced in the early part of the last decade (Lane et al., 2003; Centre for Agriculture Bioscience International, 2008). These diseases are known to produce similar effects upon certain tree and plant species within the UK in terms of leaf and plant dieback, bleeding cankers and in some cases tree mortality (P. Jennings, pers. comm.). Economic consequences of P. ramorum and P. kernoviae in the UK include extensive dieback and mortality of commercially grown Larix kaempferi (Japanese larch) (Harris and Webber, 2016), damage to ornamental plants commonly grown in plant nurseries and traded by garden centres (Chadfield and Pautasso, 2011) and potentially fewer visitors to gardens given that the quality of a garden was found by Connell (2004) as the most important factor in visitors’ enjoyment of a garden visit. Other consequences arise from the impairment of ecosystem services such as climate regulation, where dead tree stands can easily catch fire and release carbon into the atmosphere (Cheatham et al., 2009), and the impact on society through loss of recreational and cultural value (Grünwald et al., 2008). The UK government has a monitoring and containment programme in

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

place to help isolate new outbreaks once identified (Defra, 2014). However, despite these efforts P. ramorum, and to a lesser extent P. kernoviae, have continued to spread, especially in the southwestern regions of the UK. At the beginning of 2011, the spread of P. ramorum and P. kernoviae was largely limited to South West England and South Wales, thus presenting an ideal opportunity to evaluate policy options to contain P. ramorum and P. kernoviae while changes in policy direction could still significantly influence the spread of these diseases. Specifically, this paper aims to establish the public value at risk in England and Wales from a cessation of control measures in 2011 that would allow P. ramorum and P. kernoviae to spread unimpeded across the two countries. The public value at risk consists of non-extractive use and non-use values, with the former composed of recreational activities, such as walking, cycling and sightseeing, that arise from the direct public enjoyment of heritage gardens, heathland and woodland. The latter values consist of public value derived from knowing these habitats remain unchanged in order to have the option of future use and/or for altruistic or bequest motives. While there are many non-market valuation studies that estimate the public value at risk from invasive forest pests (Miller and Lindsay, 1993; Kramer et al., 2003; Moore et al., 2011), currently there is a lack of studies focusing on the public values preserved from programmes to control forest diseases. This paper aims to go some way towards filling this research gap by eliciting the public's willingness to pay (WTP) to protect habitats in England and Wales from the tree and plant diseases P. ramorum and P. kernoviae. Contingent valuation (CV) was used as the non-market valuation technique to estimate this WTP, which is representative of the public value at risk from continued P. ramorum and P. kernoviae spread into heritage gardens, heathland and woodland within England and Wales. This estimation of public value at risk may prove useful for policymakers seeking to conduct cost-benefit analyses of publicly funded programmes to contain invasive tree and plant diseases. This paper proceeds with a literature review in Section 2 of the history of P. ramorum and P. kernoviae, the tree and plant species most susceptible to infection and the ecosystem services associated with heritage gardens, heathland and woodland. Section 2 concludes with a review of existing non-market valuation literature to illustrate the public values at risk from the degradation of ecosystem services caused by various invasive forest species. Section 3 describes the CV survey used to assess the public's WTP to prevent further spread of these diseases. The results from the CV survey are presented in Section 4 in which stated public WTP values are used to estimate the public value at risk from the removal of control options. Section 5 discusses the public value at risk estimates in light of the costs of maintaining control options, as well as summarising the caveats and limitations of the process used to produce these estimates. 2. Literature review The pathogen P. ramorum was first discovered in the mid 1990's infecting oak forests along the California, USA coastline (Garbelotto et al., 2001). Within the UK, P. ramorum was first discovered at a nursery in February 2002 (Lane et al., 2003), while P. kernoviae was first discovered in October 2003 during inspections for P. ramorum (Centre for Agriculture Bioscience International, 2008). As of December 2008 most P. ramorum and P. kernoviae infections have occurred in the southwestern regions of the UK as these regions offer the most accommodative climate to these diseases in terms of warmth and moisture (Walters et al., 2009). The full host list for P. ramorum and P. kernoviae (FERA, 2010a,b) was uncertain as of

137

2010 given the rapidly evolving host range up to this point in time. However, the most recent host lists for P. ramorum and P. kernoviae (FERA, 2015a,b) indicate a largely unchanged host range for these diseases since 2010. The major sporulating hosts for these diseases are thought to be Vaccinium myrtillus (bilberry), Rhododendron ponticum (rhododendron), Japanese larch, Magnolia grandiflora (magnolia), Pieris floribunda (pieris), Viburnum tinus (viburnum) and Camellia japonica (camellia) (P. Jennings, pers. comm.). However, other hosts, such as Aesculus hippocastanum (horse chestnut), Castanea sativa (sweet chestnut), Fagus sylvatica (beech) and Quercus robur (oak), are also vulnerable to both Phytophthora diseases if they are located in close proximity to major sporulating hosts. Infection of host species by P. ramorum and P. kernoviae can lead to leaf and plant dieback and bleeding cankers (P. Jennings, pers. comm.). Many of the aforementioned tree and plant species are found in habitats such as heritage gardens, heathland and woodland. Collectively these habitats provide cultural, provisioning and regulatory ecosystem services, which are subsequently defined by the Millennium Ecosystem Assessment (2003). For instance, cultural ecosystem services are defined as ‘the nonmaterial benefits people obtain from ecosystems through spiritual enrichment, cognitive development, reflection, recreation and aesthetic experiences’, provisioning ecosystem services are defined as ‘the products obtained from ecosystem services, such as food, fuel, fiber, fresh water and genetic resources’, while regulatory ecosystem services are defined as ‘the benefits people obtain from the regulation of ecosystem processes’, such as climate regulation and water purification. In comparison to other habitats, like heathland and woodland, it is rather more difficult to precisely define a heritage garden. However, the most appropriate definition of a heritage garden is of an ornamental garden of special historic and horticultural interest arising from; the beauty, diversity or rarity of the tree and plant species on offer, the historical context of a garden and the specific landscape features on offer. These gardens provide considerable cultural ecosystem services as they provide visitors with aesthetic pleasure, time and space for contemplation, and an educational resource by improving visitor knowledge of and accessibility to the tree and plant species in heritage gardens. However, the immediate visual impact of P. ramorum and P. kernoviae infection will have a detrimental effect on the cultural ecosystem services offered by heritage gardens. This is because the leaf and plant dieback and bleeding cankers that are associated with P. ramorum and P. kernoviae infection of host species (P. Jennings, pers. comm.) will reduce the aesthetic appeal of these gardens to visitors. Control measures, such as restricting the movement of visitors and largescale removal of vegetation, are likely to further detract from the experience of tourists. Heathland is defined as a habitat dominated by a dwarf-scrub landscape, which is characterised by open low woody vegetation such as Calluna vulgaris (heather) and Vaccinium myrtillus (bilberry). Heathland is a characteristic habitat of northern Europe and has been a feature of the UK landscape for around 6000 years. This type of habitat principally provides cultural ecosystem services in the form of recreational and aesthetic experiences from activities such as walking and cycling, while a provisioning ecosystem service is provided in the form of game shooting. Heathland also provides a regulatory ecosystem service by contributing towards international climate regulation service through carbon storage, with Alonso et al. (2012) estimating 29.8 Mt of primarily soil carbon stored in English heathland. The dieback of bilberry from P. ramorum and P. kernoviae infection (FERA, 2015a,b) may cause some above ground carbon to be lost due to a greater fire risk arising from the dead combustible material produced by bilberry dieback, but the

138

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

release of soil carbon is dependent on the severity of fire outbreaks. In addition, the stem lesions and dieback of bilberry that arise from P. ramorum and P. kernoviae infection (FERA, 2015a,b) are likely to impact the aforementioned cultural ecosystem services through a less aesthetically pleasing environment for recreationalists, while the provisioning ecosystem service of game shooting may be affected by the imposition of restrictions on movement that help contain the diseases. Woodland may be defined as a habitat where trees are the dominant plant form, together with some combination of grass, flowers and shrubs. Cultural ecosystem services are also provided by woodland through recreational activities such as walking and cycling, which are heavily dependent on the aesthetic appeal of woodland. This habitat also provides a provisioning ecosystem service in the form of timber for construction. In addition, woodland provides an important regulatory ecosystem service with respect to the global climate due to the sequestration of carbon in wood and soil (Brainard et al., 2006; Cannell, 1999; Cannell et al., 1993). The leaf and plant dieback and bleeding cankers that arise from the infection of host species by P. ramorum and P. kernoviae (P. Jennings, pers. comm.) will degrade the cultural ecosystem services offered by woodland insofar as reducing the aesthetic appeal of these tree and plant species. Furthermore, the dieback and mortality of commercially grown Japanese larch from P. ramorum (Harris and Webber, 2016) will diminish this timber provisioning ecosystem service, which may result in less timber available for the construction industry. The regulatory ecosystem service of climate regulation that is provided by woodland may also be compromised by P. ramorum as carbon is potentially released into the atmosphere from dead tree stands that easily catch fire (Cheatham et al., 2009). The negative impacts to the health of trees and plants, and the associated degradation to ecosystem services, are quantified by the non-market valuation literature through studies that measure the public value at risk arising from the loss of ecosystem services. For instance, Miller and Lindsay (1993) find that households are willing to pay in 1991 an annual average of US$69 for gypsy moth control in New Hampshire, while Kramer et al. (2003) find an annual median WTP of US$28 per person in 1991 to protect remaining spruce-fir forests in the southern Appalachian Mountains in the context of forest degradation caused by the balsam woolly adelgid. In addition, Moore et al. (2011) discover an annual median WTP over 3 years of US$60e122 per respondent in 2006 for protecting hemlock forests in the southeastern US against the hemlock woolly adelgid. Some other non-market valuation studies to elicit public WTP to protect trees and plants from invasive species include Chang et al. (2011) that find mean annual WTP over 5 years of CAD$33e104 per household in 2007 for controlling outbreaks of spruce budworms and forest tent caterpillars in the Canadian provinces of New Brunswick and Saskatchewan, and Jetter and Paine (2004) who find a mean annual WTP over 7 years to control the eucalyptus snout beetle of US$23 and US$131 per respondent depending on treatment options, while a one-off WTP of US$485 per respondent is elicited for a third treatment option (survey year unknown). While there is ample literature on non-market values associated with the control of invasive forest pests, there appears to be very limited research conducted to elicit the non-market values from initiatives to control forest diseases. To the best of the authors’ knowledge the only studies to uncover the non-market value of controls to limit the spread of forest diseases are Areal and MacLeod (2007) and Meldrum et al. (2013). The former study elicits an annual WTP of £55 over 5 years per respondent to protect trees in the English countryside susceptible to P. ramorum, although the sample size was rather limited at 40 respondents and the year of survey could not be ascertained. The latter study finds a one-off WTP of US$154 per respondent in 2010 for a programme to

manage white pine blister rust across the high-elevation white pine forests of western USA. 3. Methodology The optimal valuation methodology to assess the public value at risk from P. ramorum and P. kernoviae spread has to be capable of measuring both public use and non-use values at risk, while also valuing changes that have not yet occurred through hypothetical scenarios. Choice experiments and CV surveys are stated preference methodologies that satisfy both criteria. A CV survey was selected as this methodology is better suited to analysing the value of an overall policy package (Hanley et al., 1998). Key to any non-market environmental valuation study is the definition of a counterfactual or baseline scenario from which changes are valued by the public. The counterfactual in this study was for the current spread to be contained 20 years into the future. The alternative scenario, which survey respondents were asked their WTP to avoid, was an uncontrolled spread of P. ramorum and P. kernoviae caused by the removal of control measures. These control measures consist of inspection and surveillance work, including inspections at plant passporting nurseries and retail premises, and the removal of infected sporulating host plants, especially rhododendron and larch (Defra, 2014). The difference between the two scenarios is the public value at risk that was measured using the CV survey. A pilot CV survey was developed to elicit the public's WTP to prevent P. ramorum and P. kernoviae from further spreading to heritage gardens, heathland and woodland. The survey design was piloted online to 44 members of the public on 5th January 2011 using the market research company Research Now. Respondents were asked whether they understood the following aspects of the survey; information on tree diseases, photographs of diseased species, disease spread maps and questions on WTP. Approximately two-thirds to three-quarters of respondents indicated they understood such aspects. In addition, we included a comments page for respondents to suggest improvements to the survey. These suggestions resulted in the maximum WTP tick box option of £50 being extended to £75 and £100 to account for those respondents with a true WTP in excess of £50 but who did not want to expend the extra effort involved in manually entering an amount above £50. The CV survey (Fig. S1, Electronic supplementary materials) commenced with asking respondents their age, gender and region of residence in order to stratify on the basis of these characteristics. A map showing a regional breakdown of England and Wales was presented to help respondents identify their region according to the following divisions: Channel Islands, East of England, East Midlands, London, North East, North West, Northern Island, Scotland, South East, South West, Wales, West Midlands and Yorkshire and Humberside. The survey proceeded to present respondents with definitions of heritage gardens, heathland and woodland. The survey continued with a visualisation of the impact of infection upon the most susceptible tree and plant species listed in the literature review, plus hosts such as beech and sycamore. This was achieved by showing photos of healthy and infected tree and plant species. The selection of suitable photographs for inclusion into the survey was determined through consultation with plant disease experts at the Food and Environment Research Agency (FERA) to ensure that tree and plant damage caused by P. ramorum and P. kernoviae was accurately depicted. The next section of the CV survey presented respondents with maps illustrating the current spread (December 2010) of P. ramorum and P. kernoviae and the projected spread of the diseases in 20 years i.e. up to the year 2031. These maps were created by FERA and Cambridge University to inform survey respondents about the regional variation in P. ramorum and P. kernoviae spread. The latter map was created by firstly undertaking Species

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

Distribution Modelling (SDM) using maximum entropy (Phillips et al., 2004, 2006) to produce host maps at a 1 km scale for the following four host species considered at risk from these diseases: Arctostaphylos uva-ursi (bearberry), Vaccinium vitis-idaea (cowberry), bilberry and rhododendron. The environmental factors considered in the model included climate, soil and topography. Secondly, the distributions produced by the SDM were further refined by clipping with the following categories of the Land Cover Map 2000 (LCM2000): bog, bracken, broadleaf/mixed woodland, coniferous woodland, dwarf shrub heath and montane. These categories correspond to habitats expertly judged as suitable for growth of the specific host species. Without this refinement an incorrect assumption would have been made that each host species fills the entirety of each 1 km2 cell. The LCM2000 refined SDM outputs for all species were incorporated into the full host map for the Metapopulation Epidemic Model (MPEM) developed by Cambridge University. This map consists of FERA host maps and the National Inventory of Woodland and Trees (NIWT) and larch distribution from the Forestry Commission database containing spatial data on all Forestry Commission larch in the UK. A 20 year simulation was used in the MPEM, which produced two raster files: a hazard map showing the risk posed of P. ramorum and P. kernoviae spreading to each raster cell (assuming the disease could spread to all cells of the map) and a map showing the probability of the disease actually spreading from its current positions to each 1 km2 cell of the map. These two files were combined to produce a raster output showing the hazard posed to each cell from disease spread, weighted by the probability that the diseases would reach that cell. This is the final risk map that was used to illustrate the spread of P. ramorum and P. kernoviae to the year 2031. Further maps were presented immediately prior to the WTP questions showing the location of heritage gardens, heathland and woodland in England and Wales, as well as reminders as to the tree and plant species at risk in each of these habitats. Comparing these location maps with the risk map for the year 2031 enabled respondents to identify the risk of P. ramorum and P. kernoviae to habitats in their home region. Respondents were then asked for their maximum WTP to stop further P. ramorum and P. kernoviae spread to heritage gardens, heathland and woodland in; a) respondents' own regions and b) elsewhere in England and Wales (henceforth denoted as other national habitats). This culminated in each respondent being asked a total of six WTP questions. Respondents were informed that the costs associated with measures to protect the three habitats from P. ramorum and P. kernoviae would be met through a higher yearly income tax. The WTP elicitation format consisted of a payment ladder of tick boxes representing 18 maximum WTP amounts ranging from £0.20 to £100. Additional tick boxes were inserted for respondents who wanted to manually enter a maximum WTP amount or to indicate a zero WTP. Respondents were asked to select one tick box for each of the six WTP questions. A respondent's stated WTP to protect regional and other national habitat types were summed and presented back to the respondent, who subsequently had the option to revise the WTP amounts previously stated. 4. Results and discussion 4.1. Analysing the CV survey data The final survey was distributed online by the market research company Research Now, to 959 people (excluding speeders1)

1 ‘Speeders’ are identified as those respondents who take an insufficient amount of time to consider and complete the online survey.

139

during the period 28th January to 4th February 2011. However, 32 respondents were identified as providing protest bids and were removed from the sample. These respondents were identified from questions asking reasons for providing zero WTP values, whereby such respondents stated they already paid too much tax and/or did not believe income tax should be used for protecting habitats from P. ramorum and P. kernoviae spread. This reduced the sample size to 927 respondents for data analysis. Respondents were selected using proportionate stratification on the basis of gender, age and region/ country of residence. Table 1 shows a close resemblance between the sample and the adult population in England and Wales in terms of gender and age. In addition, there was an even spread of respondents sampled from across the English regions and Wales, although there was an oversampling of respondents with membership of an environmental organisation. The results of the CV survey were analysed using the statistical software package Stata and are presented within Table 2. This shows the greatest public value at risk is from spread to heritage gardens, while lower public value is lost should woodland and heathland become further infected. The proximity of habitats to a respondent's place of residence is shown to have an impact on respondents' WTP to protect such habitats as respondents are willing to pay more to protect local habitats compared to other national habitats located in other regions of England and Wales. This is most likely due to the distance decay effect whereby people are less likely to travel to habitats as the distance to these habitats increases. Indeed it is noteworthy from Table 2 that the greatest difference between WTP values for regional and other national habitats is for heritage gardens and woodland, which have a higher proportion of the sample who are users compared to heathland. This is logical as one would expect a greater distance decay effect for habitats that are used by the public. The ordering of WTP questions, starting with questions asking a respondent's WTP for heritage gardens and finishing with questions about a respondent's WTP for woodland, did not have an impact on the WTP for the three habitat types. The absence of such an ordering bias is confirmed in the CV survey as no evidence arose of the public either consistently increasing or decreasing their WTP as the number of questions answered increased (Table 2). Results from the CV survey were further analysed using interval regression analysis conducted in the statistical software package Stata to evaluate the impact of various socio-demographic characteristics of respondents on the WTP to protect habitats from P. ramorum and P. kernoviae. The backward stepwise method was the econometric approach used for the interval regression analysis in which the most insignificant socio-demographic variables are removed. The results of this analysis are shown in Table 3 in which a respondent's income and concern over the spread of these diseases have a significant positive impact on WTP. These sociodemographic influences on WTP are both logical and to be expected. However, before aggregating the mean WTP values in Table 2 to the national population levels of England and Wales, it was necessary to account for the overrepresentation of the public with membership of an environmental organisation seen in Table 1. Indeed the regression analysis results shown in Table 3 reveal members of environmental organisations are willing to pay premiums of £1.86, £1.83 and £1.16 to stop further P. ramorum and P. kernoviae spread into regional heritage gardens, other national heritage gardens and other national heathland from infection respectively. The adjustment to mean WTP values was made by multiplying the aforementioned premiums by the oversampling percentage of 22.1% (Table 1). This resulted in a downward adjustment to the mean WTP values presented in Table 2 to £7.24, £6.14 and £4.08 to protect regional heritage gardens, other national

140

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

Table 1 Target and actual stratification of the survey sample.

Gender

Male Female 18-34 Years 35-59 Years 60 þ Years East of England East Midlands London North East North West South East South West Wales West Midlands Yorkshire & Humber Yes No

Age

Region

Environmental Membershipb

Stratification targeta

Sample

48.7% 51.3% 28.6% 43.0% 28.5% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 90%

47.9% (n ¼ 444) 52.1% (n ¼ 483) 28.4% (n ¼ 263) 43.5% (n ¼ 403) 28.2% (n ¼ 261) 9.9% (n ¼ 92) 9.6% (n ¼ 89) 9.8% (n ¼ 91) 10.2% (n ¼ 95) 10.4% (n ¼ 96) 10.0% (n ¼ 93) 10.2% (n ¼ 95) 10.1% (n ¼ 94) 9.8% (n ¼ 91) 9.8% (n ¼ 91) 32.1% (n ¼ 298) 67.9% (n ¼ 629)

a

Office for National Statistics (2010a). Stratification targets for gender and age are based on the adult (18 years þ) population in England and Wales. The number people in the UK population with membership of an environmental organisation is determined using membership figures for the following organisations: National Trust, RSPB, English Heritage, Friends of the Earth, Greenpeace, Historic Scotland, Royal Horticultural Society and the Woodland Trust. An assumption is made that the proportion of people in the UK with membership of an environmental organisation is similar to the population in England and Wales. b

Table 2 Mean annual WTP to prevent spread to habitats.a Heritage gardens

All respondents Users Non-Users Proportion of Sample that are Users

Heathland

Woodland

Regional

Other national

Regional

Other national

Regional

Other national

£7.65 £8.77 £4.68 72.6% (n ¼ 673)

£6.54 £7.72 £3.39

£4.86 £6.11 £2.34 67.0% (n ¼ 621)

£4.34 £5.67 £1.66

£6.12 £7.04 £2.85 78.2% (n ¼ 725)

£5.04 £5.93 £1.84

a The location of regional habitats was defined to survey respondents as a respondent's place of residence in accordance with the former Government Offices for the Regions (GORs) boundary classifications (Office for National Statistics, 2010b), while national habitats were defined as habitats which exist in the rest of England and Wales but not within a respondent's particular region.

Table 3 Interval regression analysis of socio-demographics variables on WTP. Socio-demographic variable

Male Income (£1000 increase) Heard of Pr, Pk or SOD Noticed pests/diseases on trees/plants Member of conservation, environmental or gardening organisation Number of times visited HGs in England and Wales over last 12 months. Number of times visited HE in England and Wales over last 12 months. Number of times visited WD in England and Wales over last 12 months. Increased concern about Pr and Pk damaging HGs (likert scale) Increased concern about Pr and Pk damaging HE (likert scale) Increased concern about Pr and Pk damaging WD (likert scale) Log L Wald Chi-Square ML (Cox-Snell) R2

WTP heritage gardens

WTP heathland

WTP woodland

Regional

Other national

Regional

Other national

Regional

Other national

0.32 0.07*** 2.38** 1.37 1.86* 0.22 e e 1.27*** e e 3402.52 48.51 0.058

0.83 0.05** 1.22 1.73** 1.83** 0.21 e e 1.16*** e e 3424.23 37.36 0.048

0.09 0.07*** 1.36** 1.21** 0.88 e 0.04 e e 1.10*** e 3276.06 42.76 0.065

0.55 0.04*** 1.24* 1.20** 1.16* e 0.03 e e 1.18*** e 3253.54 43.33 0.061

0.25 0.08*** 2.04** 1.06 0.54 e e 0.03 e e 2.21*** 3400.02 54.51 0.082

0.85 0.06*** 1.36* 1.06 0.84 e e 0.02 e e 1.88*** 3349.64 46.75 0.073

* ¼ Significant at 10% level, ** ¼ Significant at 5% level, *** ¼ Significant at 1% level.

heritage gardens and other national heathland respectively. The adjusted mean WTP values were then aggregated up to national level by multiplying by the 43 million people aged 18 years or older living in England and Wales (Office for National Statistics, 2010a). A similar approach is used by Meldrum et al. (2013) to aggregate average household WTP to control white pine bluster rust up to the total number of households in western USA. These figures are presented in Table 4. In addition, Table 4 contains aggregated WTP values based on different assumptions regarding the proportion of the population

who are users of the habitats.2 This sensitivity analysis is necessary as it is not clear from the literature whether the sample truly represents the actual proportion of users and non-users in the

2 The estimates of aggregated WTP generated from assumptions that all of the population are users or non-users do not take into account the oversampling of the public with membership of environmental organisations. This is because the adjustments made to WTP values to account for this oversampling were estimated in Stata from a regression analysis of the whole sample of 927 respondents.

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

141

Table 4 Aggregated annual WTP to prevent spread to habitats.

Assuming 100% of Population are Users (Upper Bound) Mean WTP Adjusted for Environmental Membership Assuming 100% of Population are Non-Users (Lower Bound)

Heritage gardens

Heathland

Regional

Other national

Regional

Other national

Regional

Other national

£379 m £313 m £202 m

£333 m £265 m £146 m

£264 m £210 m £101 m

£245 m £176 m £72 m

£304 m £264 m £123 m

£256 m £218 m £79 m

population. With this in mind, the aggregated WTP values derived from the assumption that all adults in the population are users should be treated as upper bound estimates, while the aggregated WTP values derived from assuming no habitat users should be treated as conservative estimates. These aggregated WTP values are combined on a per habitat basis and presented in Table 5. This shows heritage gardens as the habitat with the most public value at risk from P. ramorum and P. kernoviae, while the smallest public value at risk comes from infected heathland. Summing the public WTP values across all habitats demonstrates that substantial public value is at risk regardless of whether one assumes an English and Welsh population dominated by users or non-users. For instance, even when making a highly conservative assumption that there are no users of heritage gardens, heathland and woodland in England and Wales, the public value at risk from P. ramorum and P. kernoviae spread still totals £723 m per year. Conversely, assuming that all of the population of England and Wales are users of heritage gardens, heathland and woodland yields a public value at risk figure of £1,781 m. 4.2. Discussion of the CV survey results On a per person basis the CV survey produced an annual WTP of £33.48 to protect these habitats from P. ramorum and P. kernoviae, which includes an adjustment to correct for an overrepresentation of the public with membership of an environmental organisation. This WTP is much smaller than the annual WTP of £55 found by Areal and MacLeod (2007) in their study of the public WTP to protect trees in the English countryside from P. ramorum and P. kernoviae. One can hypothesize the difference in WTP values may result from Areal and MacLeod (2007) surveying staff exclusively from the Central Science Laboratory (now FERA) at York, UK, who employ tree and plant health scientists amongst other disciplines. Consequently respondents surveyed by Areal and MacLeod (2007) may have had a self-interest to overbid in the survey and/or be in possession of greater knowledge of the diseases compared to the general public. In addition, annual payments were limited to five years in Areal and MacLeod (2007) whereas in this study the annual payments did not have a specified end date. The authors hypothesize that this may also have contributed towards higher WTP values in Areal and MacLeod (2007) as people may be more inclined to state a higher annual WTP value if the period of payments is finite compared to an infinite or unspecified duration of payments, other things remaining constant. Another factor that may

Woodland

explain disparities in WTP values between the studies is the much higher sample size for this study compared to Areal and MacLeod (2007). Focusing specifically on the values contained in Table 5, the public value at risk from P. ramorum and P. kernoviae spread upon assuming 100% of the population are non-users of heritage gardens, heathland and woodland can be interpreted as public non-use values that are at risk from these diseases. This interpretation implicitly assumes that a user of these habitats hold the same nonuse values as a non-user as it is likely the overall population consists of some habitat users. The implicit non-use values in Table 5 that are at risk from P. ramorum and P. kernoviae spread are therefore £348 m, £173 m and £202 m per year for heritage gardens, heathland and woodland respectively. These non-use values may arise from a number of motives held by the public. For instance, the public may hold altruistic and bequest values, with the former arising out of a desire for others to have access to uninfected habitats, with the latter arising from a desire that future generations should also enjoy access to the same uninfected habitats. Non-use values may also arise from the public holding option values such that members of the public wish to see the habitats remain free of P. ramorum and P. kernoviae in order to have the option of using the habitats at some point in the future. The size of non-use values measured by non-market valuation studies are thought to be influenced by the level of substitutability between the asset of value and other alternative assets. For instance, Bateman et al. (2002) see non-use values as especially important where the good being valued has few or no substitutes. This is pertinent to heritage gardens, heathland and woodland as it may be difficult to replicate the current composition of trees and plants in these habitats, on a sufficiently large scale, if P. ramorum and P. kernoviae becomes widespread in England and Wales. In this situation few substitute sites would exist. This may help explain why this study recorded non-use values as evidenced by non-users of heritage gardens, heathland and woodland being willing to pay to prevent infection of these habitats. At this point it is useful to discuss the non-use values detected in this study in a temporal context. In the short-term the spread of P. ramorum and P. kernoviae may indeed limit the existence of substitute sites containing the tree and plant species under threat from these diseases. However, as time progresses the public may come to appreciate alternative tree and plant compositions that do not include species threatened by P. ramorum and P. kernoviae. The passage of time may also fade public memories of the tree and plant species affected by P. ramorum and P. kernoviae such that the non-

Table 5 Public value at risk, by habitat, from P. ramorum and P. kernoviae spread to 2031. Heritage gardens

Heathland

Woodland

Total public value at risk

£509 m £386 m £173 m

£560 m £482 m £202 m

£1,781 m £1,446 m £723 m

Annual WTP values Assuming 100% of Population are Users (Upper Bound) Mean WTP Adjusted for Environmental Membershipa Assuming 100% of Population are Non-Users (Lower Bound) a

£712 m £578 m £348 m

The sample of respondents from the CV survey declaring their use of heritage gardens, heathland and woodland is 72.6%, 67.0% and 78.2% respectively.

142

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

use values associated with these species become irrelevant if their existence is erased from the public's consciousness. A relevant example here are the pathogens associated with Dutch Elm Disease, Ophiostoma. ulmi and Ophiostoma. novo-ulmi, which have destroyed the majority of Elm trees in the British countryside. This has led to most people born in Britain since the 1970s not knowing what an Elm tree landscape looks like (Seddon, 2010), which makes it difficult for this generation to form non-use values for such a landscape. The implications here for the non-use values detected in this study are that these values could decline in importance over time if the trees and plants most susceptible to P. ramorum and P. kernoviae are decimated. In addition, this study identified public use values that may be at risk from a further spread of P. ramorum and P. kernoviae in England and Wales. These use values are deduced in Table 5 by subtracting the non-use values of £348 m, £173 m and £202 m for heritage gardens, heathland and woodland respectively from the mean aggregated WTP for these habitats that has been adjusted for an overrepresentation of the public with membership of an environmental organisation. This calculation yields public use values at risk of £230 m, £213 m and £280 m per year for heritage gardens, heathland and woodland respectively. These use values are most likely to be composed of cultural ecosystem service values as the aesthetic impact of P. ramorum and P. kernoviae, as illustrated in the CV survey, is most likely to impact on the recreational activities offered by the habitats, such as walking, cycling and educational resource offered by heritage gardens. Furthermore, the CV survey did not highlight the regulatory ecosystem service of carbon sequestration that is provided by heathland and woodland, while the provisioning ecosystem services, such as timber from commercial larch plantations, are private goods that are not freely accessible to the public. Comparing the public use values generated from this study with the relevant literature is somewhat difficult given the lack of alternative studies into the non-market value of heritage gardens, heathland and woodland. However, a comparison may be made with Scarpa (2003) who find a recreational value of £368 m per year in 2002 for forests in England and Wales, which is some £90 m per year higher than comparable woodland values found in this study. In addition, Garrod (2002) find a landscape value of approximately £130 m per year in 2002 for woodland in England and Wales, exclusive of recreational value. This landscape value reflects the value to the public of woodland views from houses and on journeys. Unfortunately this study does not elicit landscape values associated with woodland, although inclusion of such values would further add to the public value at risk from further P. ramorum and P. kernoviae spread in England and Wales. However, some caveats should be acknowledged upon interpreting the public value at risk figures within Table 5. The first caveat concerns the definition of the counterfactual or baseline scenario, which assumes no further spread of P. ramorum or P. kernoviae from a continuation of current Phytophthora controls. This assumption is unrealistic as some disease spread is likely even with a continuation of current controls. The potential therefore exists for an overestimation of the public value at risk as the level of avoidable damage, which is the difference between the alternative and counterfactual scenarios, may be too high. A second caveat concerns the lack of available data on the proportion of the public in England and Wales using heritage gardens, heathland and woodland. In the CV survey the proportion of respondents using heritage gardens, heathland and woodland is 72.6%, 67.0% and 78.2% respectively. Unfortunately there is no way of knowing whether these proportions introduce a sampling bias, or in which direction such a bias influences the results generated

by this study. 5. Conclusions This study used a CV survey to estimate £1.446bn of nonextractive public value is at risk per year in the absence of control measures to halt the spread of P. ramorum and P. kernoviae in England and Wales. However, even if one makes a highly conservative assumption that there are no users of these habitats in England and Wales, the results from this study still indicate substantial public value at risk of £723 m per year from the spread of these diseases. Given that the costs of the UK government's monitoring and containment programme for the diseases amounted to £25 m over the initial 5-year period of the programme (Marshall, 2009), the subsequent rolling forward of the programme (Defra, 2014) appears to be good value for money in light of the public value at risk estimates produced by this study. These estimates are substantially higher than the commercial value of larch in Great Britain, which is estimated by Defra (2014) at £60 m per year. A continuation of the current P. ramorum and P. kernoviae control programme will therefore preserve public value of a greater magnitude than the commercial value of larch in the forestry sector. In terms of policymaking, the considerable public value at risk found by this study justify at the very least a continuation of the current control programme. Furthermore, these estimates of public value at risk may be used to parameterise cost-benefit analyses of future programmes to control P. ramorum and P. kernoviae. This would help policymakers demonstrate the benefits that would accrue to the public in advance of commitments to publicly fund these programmes. The estimates of public value at risk produced by this study may also be used, subject to international agreement, to modify British trade policies to internalise the negative impact of P. ramorum and P. kernoviae in England and Wales. This modification, as highlighted by Holmes et al. (2009), may include imposing tariffs to shift the costs and losses of invasive pests onto responsible economic sectors to produce an optimal reduction in risk. While Holmes et al. (2009) refer to these costs as the costs incurred by the taxpayer and private forest landowners, in principle there is no reason why the public value costs of P. ramorum and P. kernoviae cannot be treated in the same manner. Estimates of public value at risk from P. ramorum and P. kernoviae would help to inform an appropriate level of tariff that would internalise some of the public value lost to these diseases into the cost of products that act as pathways for the diseases. While this study uncovered substantial public value is at risk from the spread of P. ramorum and P. kernoviae, further research efforts are recommended by the authors to improve the accuracy of future estimates of the public value at risk from the spread of tree and plant diseases. One key advance would be to identify the proportion of national populations visiting and using heritage gardens, heathland and woodland. This information would help to remove sampling bias should a sample of respondents to a nonmarket valuation survey not be representative of the visitation habits of the wider population. This would enable greater confidence to be realised in future efforts to estimate the public use values at risk from the degradation of habitats. Another avenue for future research would be to investigate the public's WTP to protect UK habitats against other invasive tree and plant diseases, especially against emerging threats such as Xylella fastidiosa and Cryphonectria parasitica (Forestry Commission, 2016a,b). This would help policymakers determine which diseases represent the greatest threat to the public's value of habitats and to prioritise resources to containment programmes accordingly. Currently there is very limited non-market environmental valuation literature with which policymakers can base containment decisions on. It is the sincere

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

hope of the authors that a future abundance of such studies provide policymakers globally with a broader evidence base on which to allocate public resources for the purpose of protecting habitats from invasive tree and plant diseases. Acknowledgements The authors are indebted to the team at FERA including Nigel Boatman, Kate Somerwill, Alan Inman, John Hughes, Keith Walters, Claire Sansford, and Judith Turner. We would also like to thank Erik DeSimone for constructing the P. ramorum and P. kernoviae spread maps. In addition, the authors are thankful for the assistance and information provided by Bruce Rothnie, Jennifer Mcvey, Pat Snowdon, Olly Stephenson, Justin Gilbert, Shona Cameron and Mark Broadmeadow (Forestry Commission), Susana Mourato (LSE), Suzanne Perry and Keith Kirby (Natural England) and Ian Wright (National Trust). The authors would also like to thank the market research company Research Now for administering the survey to the public, the Defra Steering Group for the guidance provided, Defra for funding the study (research project code PG0102) and finally the two anonymous reviewers for their insightful comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2017.01.013. References Alonso, I., Weston, K., Gregg, R., Morecroft, M., 2012. Carbon Storage by Habitat: Review of the Evidence of the Impacts of Management Decisions and Condition of Carbon Stores and Sources. http://publications.naturalengland.org.uk/file/ 1438141 (Accessed 20 October 2016). Areal, F.J., MacLeod, A., 2007. Estimating the economic value of trees at risk from a quarantine disease. In: Lansink, O., Alfons, G.J.M. (Eds.), New Approaches to the Economics of Plant Health. Springer, Dordrecht, The Netherlands, pp. 119e130. Bateman, I., Carson, R., Day, B., Hanemann, M., Hanley, N., Hett, T., Jones-Lee, M., € Loomes, G., Mourato, S., Ozdemiroglu, E., Pearce, D., Sugden, R., Swanson, J., 2002. Economic Valuation with Stated Preference Techniques. Edward Elgar, Cheltenham, UK. Boyd, I.L., Freer-Smith, P.H., Gilligan, C.A., Godfray, H.C.J., 2013. The consequence of tree pests and diseases for ecosystem services. Science 342. http://dx.doi.org/ 10.1126/science.1235773, 1235773-1e1235773-8. Brainard, J., Lovett, A., Bateman, I., 2006. Sensitivity analysis in calculating the social value of carbon sequestered in british grown sitka spruce. J. For. Econ. 12, 201e228. http://dx.doi.org/10.1016/j.jfe.2006.08.002. Cannell, M.G.R., Dewar, R.C., Pyatt, D.G., 1993. Conifer plantations on drained peatlands in Britain: a net gain or loss of carbon? Forestry 66, 353e369. http:// dx.doi.org/10.1093/forestry/66.4.353. Cannell, M.G.R., 1999. Growing trees to sequester carbon in the UK: answers to some common questions. Forestry 72, 237e247. http://dx.doi.org/10.1093/ forestry/72.3.237. Centre for Agriculture Bioscience International, 2008. Phytophthora kernoviae (distribution map). Dist. Maps. Plant. Dis. 1023. Chadfield, V., Pautasso, M., 2011. Phytophthora ramorum in England and Wales: which environmental variables predict county disease incidence? For. Pathol. 42, 150e159. http://dx.doi.org/10.1111/j.1439-0329.2011.00735.x. Chang, W., Lantz, V.A., MacLean, D.A., 2011. Social benefits of controlling forest insect outbreaks: a contingent valuation analysis in two Canadian provinces. Can. J. Agric. Econ. 59, 383e404. http://dx.doi.org/10.1111/j.17447976.2010.01208.x. Cheatham, M.R., Rouse, M.N., Esker, P.D., Ignacio, S., Pradel, W., Raymundo, R., Sparks, A.H., Forbes, G.A., Gordon, T.R., Garrett, K.A., 2009. Beyond yield: plant disease in the context of ecosystem services. Phytopathology 99, 1228e1236. http://dx.doi.org/10.1094/PHYTO-99-11-1228. Connell, J., 2004. The purest of human pleasures: the characteristics and motivations of garden visitors in great Britain. Tour. Manage 25, 229e247. http:// dx.doi.org/10.1016/j.tourman.2003.09.021. Defra, 2014. Tree Health Management Plan. https://www.gov.uk/government/ uploads/system/uploads/attachment_data/file/307299/pb14167-tree-healthmanagement-plan.pdf (Accessed 15 December 2016). FERA, 2010a. Phytophthora Ramorum - A Threat to Our Woodlands, Heathlands and Historic Gardens. http://fera.co.uk/news/resources/documents/pests-diseasephytophthoraRamorumFactsheet.pdf (Accessed 19 April 2011). FERA, 2010b. Phytophthora Kernoviae - A Threat to Our Woodlands, Heathlands and Historic Gardens. http://fera.co.uk/news/resources/documents/pests-disease-

143

phytophthoraKernoviaeFactsheet.pdf (Accessed 19 April 2011). FERA, 2015a. Fera List of Natural Hosts for Phytophthora Ramorum with Symptom and Location. https://planthealthportal.defra.gov.uk/assets/uploads/Pramorum-host-list-finalupdate-NOV-20-15.pdf (Accessed 16 December 2016). FERA, 2015b. Fera List of Natural Hosts for Phytophthora Kernoviae with Symptom and Location. https://planthealthportal.defra.gov.uk/assets/uploads/P. kernoviae-host-list-finalupdateNov-2015.pdf (Accessed 16 December 2016). Forestry Commission, 2016a. Xylella Fastidiosa. http://www.forestry.gov.uk/xylella (Accessed 20 October 2016). Forestry Commission, 2016b. Sweet Chestnut Blight (Cryphonectria Parasitica). http://www.forestry.gov.uk/chestnutblight#Prospects (Accessed 2020 October 2016). Garbelotto, M., Svihra, P., Rizzo, D., 2001. Sudden oak death syndrome fells 3 oak species. Calif. Agric. 55, 9e19. http://dx.doi.org/10.3733/ca.v055n01p9. Garrod, G.D., 2002. Landscape Benefits. Social and Environmental Benefits of Forestry Phase 2. http://www.forestry.gov.uk/pdf/fclscaperep.pdf/$FILE/ fclscaperep.pdf (Accessed 13 December 2015). Grünwald, N.J., Goss, E.M., Press, C.M., 2008. Phytophthora ramorum: a pathogen with a remarkably wide host range causing sudden oak death on oaks and ramorum blight on woody ornamentals. Mol. Plant Pathol. 9, 729e740. http:// dx.doi.org/10.1111/J.1364-3703.2008.00500.x. Hanley, N., MacMillan, D., Wright, R.E., Bullock, C., Simpson, I., Parsisson, D., Crabtree, B., 1998. Contingent valuation versus choice experiments: estimating the benefits of environmentally sensitive areas in Scotland. J. Agric. Econ. 49, 1e15. http://dx.doi.org/10.1111/j.1477-9552.1998.tb01248.x. Harris, A.R., Webber, J.F., 2016. Sporulation potential, symptom expression and detection of Phytophthora ramorum on larch needles and other foliar hosts. Plant. Pathol. 65, 1441e1451. http://dx.doi.org/10.1111/ppa.12538. Holmes, T.P., Aukema, J.E., Von Holle, B., Liebhold, A., Sills, E., 2009. Economic impacts of invasive species in forests. Ann. N.Y. Acad. Sci. 1162, 18e38. http:// dx.doi.org/10.1111/j.1749-6632.2009.04446.x. Jetter, K., Paine, T.D., 2004. Consumer preferences and willingness to pay for biological control in the urban landscape. Biol. Control 30, 312e322. http:// dx.doi.org/10.1016/j.biocontrol.2003.08.004. Kovacs, K., V aclavík, T., Haight, R.C., Pang, A., Cunniffe, N.J., Gilligan, C.A., Meentemeyer, R.K., 2011. Predicting the economic costs and property value losses attributed to sudden oak death damage in California (2010e2020). Environ. Manage 92, 1292e1302. http://dx.doi.org/10.1016/j.jenvman.2010.12.018. Kramer, R.A., Holmes, T.P., Haefele, M., 2003. Contingent valuation of forest ecosystem protection. In: Sills, E.O., Abt, K.L. (Eds.), Forests in a Market Economy. Kluwer Academic Publishers, Boston, USA, pp. 303e320. Lane, C., Beales, P., Hughes, K., Griffin, R., Munro, D., Brasier, C., Webber, J., 2003. First outbreak of Phytophthora ramorum in England, on Viburnum tinus. Plant. Pathol. 52 http://dx.doi.org/10.1046/j.1365-3059.2003.00835.x, 414e414. Marshall, T., 2009. British Trees and Shrubs Face Sudden Death. http://www.nerc.ac. uk/planetearth/stories/411/ (Accessed 29 December 16). Meldrum, J.R., Champ, P.A., Bond, C.A., 2013. Heterogeneous nonmarket benefits of managing white pine bluster rust in high-elevation pine forests. J. Econ. 19, 61e77. http://dx.doi.org/10.1016/j.jfe.2012.10.001. Millennium Ecosystem Assessment, 2003. Ecosystems and Human Well-being: A Framework for Assessment. Island Press, Washington D.C., USA. Miller, J.D., Lindsay, B.E., 1993. Willingness to pay for a state gypsy moth control program in new Hampshire: a contingent valuation case study. J. Econ. Entomol. 86, 828e837. http://dx.doi.org/10.1093/jee/86.3.828. Moore, C.C., Holmes, T.P., Bell, K.P., 2011. An attribute-based approach to contingent valuation of forest protection programs. J. Econ. 17, 35e52. http://dx.doi.org/ 10.1016/j.jfe.2010.09.001. Office for National Statistics, 2010a. Population Estimates for UK, England and Wales, Scotland and Northern Ireland e Mid 2009. http://www.ons.gov.uk/ons/ rel/pop-estimate/population-estimates-for-ukeengland-and-walesescotlandand-northern-ireland/2009/index.html (Accessed 22 October 2010). Office for National Statistics, 2010b. Regions (Former GORs). http://www.ons.gov. uk/ons/guide-method/geography/beginner-s-guide/administrative/england/ government-office-regions/index.html (Accessed 21 October 2010). Phillips, S.J., Dudik, M., Schapire, R.E., 2004. A maximum entropy approach to species distribution modeling. In: Proc. 21st Intl. Conf. on Machine Learning, pp. 655e662. http://dx.doi.org/10.1145/1015330.1015412. Phillips, S.J., Anderson, R.P., Schapire, R.E., 2006. Maximum entropy modeling of species geographic distributions. Ecol. Model. 190, 231e259. http://dx.doi.org/ 10.1016/j.ecolmodel.2005.03.026. Pimentel, D., Zuniga, R., Morrison, D., 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecol. Econ. 52, 273e288. http://dx.doi.org/10.1016/j.ecolecon.2004.10.002. Potter, C., Harwood, T., Knight, J., Tomlinson, I., 2011. Learning from history, predicting the future: the UK Dutch elm disease outbreak in relation to contemporary tree disease threats. Philos. Trans. R. Soc. B 366, 1966e1974. http:// dx.doi.org/10.1098/rstb.2010.0395. Santini, A., Ghelardini, L., De Pace, C., Desprez-Loustau, M.L., Capretti, P., Chandelier, A., Cech, T., Chira, D., Diamandis, S., Gaitniekis, T., Hantula, J., Holdenrieder, O., Jankovsky, L., Jung, T., Jurc, D., Kirisits, T., Kunca, A., Lygis, V., Malecka, M., Marcais, B., Schmitz, S., Schumacher, J., Solheim, H., Solla, A., , I., Tsopelas, P., Vannini, A., Vettraino, A.M., Webber, J., Woodward, S., Szabo Stenlid, J., 2013. Biogeographical patterns and determinants of invasion by forest pathogens in Europe. New Phytol. 197, 238e250. http://dx.doi.org/ 10.1111/j.1469-8137.2012.04364.x.

144

B. Drake, G. Jones / Journal of Environmental Management 191 (2017) 136e144

Scarpa, R., 2003. The Recreational Value of Woodlands. http://www.forestry.gov.uk/ pdf/nmbrecrep.pdf/$FILE/nmbrecrep.pdf (Accessed 12 December 2015). Seddon, M., 2010. The Decline of the English Elm Tree. http://news.bbc.co.uk/1/hi/ programmes/newsnight/8912727.stm (Accessed 17 September 2010). Walters, K., Sansford, C., Slawson, D., 2009. Phytophthora Ramorum and Phytophthora Kernoviae in England and Wales - Public Consultation and New

Programme. General Technical Report PSW-GTR-229. http://www.fs.fed.us/ psw/publications/documents/psw_gtr229/psw_gtr229_006.pdf (Accessed 15 September 2010). Watt, M., Bulman, L., Palmer, D., 2011. The economic cost of Dothistroma needle blight to the New Zealand forest industry. N. Z. J. For. 56, 20e22.