Dutch elm disease revisited: past, present and future management in Great Britain

Abstract

The arrival of a new species of the fungus which causes Dutch elm disease into Great Britain in the 1960s caused widespread elm death and continues to be problematic following elm regeneration. Attempts at managing the disease have been largely unsuccessful. Forty years after the outbreak, however, researchers continue to be interested in both the underlying biology of such a severe and dramatic disease event and in the policy lessons that can be drawn from it. We develop a spatial model at a 1 km 2 resolution. Following parameterization to replay the historical epidemic, the model is used to explore previously proposed counterfactual management strategies. A new introduction date of late 1962 is estimated. We show that, even had there been high intervention at a national level in terms of disease management early in the epidemic, there would have been little long-term effect on elm numbers. In Brighton, a local pocket of elm which survived the peak of the initial epidemic has been successfully managed. However, Brighton and similar locations are subject to repeated waves of the disease at a 15-to 20-year intervals following regeneration and reinfection of the surrounding areas, during which much more intensive management is required.Keywords: epidemiology, Ophiostoma novo-ulmi, spatial modelling, Ulmus IntroductionThroughout the 1970s an epidemic of a newly introduced Dutch elm disease fungus swept through Britain, killing the majority of mature elm trees (Gibbs, 1978a;Jones, 1981). The epidemic was caused by the scolytid bark beetle-borne fungus Ophiostoma novo-ulmi Brasier & Kirk, 2001), a new species which had not been identified at the time of introduction. This fungus had been causing widespread elm death in North America, in conjunction with the original Dutch elm disease fungus O. ulmi, which had been introduced from Europe (Gibbs, 1978b). In North America, the native elm species were very susceptible to both pathogens, and a distinction had not been made between them, although a change of disease intensity was identified (Pomerleau, 1961).In Europe, the original fungus had been causing elm death since at least the 1920s, when it was first identified. In Britain, the official line (Peace, 1960) was that the disease did not justify significant government intervention since a degree of recovery could be expected, and epidemic flareups were localized (provided that the disease did not change its character). Following the introduction of the new fungus on infected timber from Canada , there was a resurgence of the disease. In a recent analysis of the science and policy of the epidemic, Tomlinson & Potter (2010) record how the received wisdom of Peace, widely disseminated and largely accepted within plant pathology circles, had the effect of delaying a response, as the resurgence was understandably perceived as a local flareup of O. ulmi. Hindsight suggests that the potential existed for the new fungal species to be identified outside Britain, and that management could have been better coordinated and managed...

Learning from history, predicting the future: the UK Dutch elm disease outbreak in relation to contemporary tree disease threats

“…Elm (mainly Ulmus procera, Ulmus minor and Ulmus glabra) were important trees in the UK landscape, particularly the English elm, U. procera, widely planted as a hedgerow tree from the sixteenth century onwards but eventually to become one of the defining features of the lowland rural landscape after extensive planting and establishment during the parliamentary enclosures of the eighteenth century [10]. Our own estimates suggest a baseline population of 30 million elm trees of all species distributed as shown in figure 1a, with over half the elms concentrated in southern England [11]. By 1970, reports of elm death in various settings had increased dramatically, with hundreds of letters from gardeners, estate managers, farmers and from people making observations during walks and visits [12].…”

“…This earlier study, while valuable as a contribution to understanding how outcomes were a function of very high transmission and lethality rates, is necessarily limited by its assumptions. Our spatial model [11] treats transmission as a spatial process that affects all trees. The distribution of all British elm species in woodland, hedgerow and urban areas was mapped (based on surveys both before and during the epidemic, combined with modern raster datasets) and differences in susceptibility between species treated using a host suitability index.…”

“…The model used [11] was a 1 km 2 resolution spatial application of the SEIS model [20], treating both the disease fungus (O. novo-ulmi) and the bark beetle vectors (Scolytus spp.) as a single pathogen.…”

Representing uncertainty in a spatial invasion model that incorporates human-mediated dispersal

“…Such models, which describe a species' movement via vectors, or links, between a set of interconnected nodes, have been perhaps most commonly applied for invaders of marine environments (e.g., Floerl et al 2009), but also to depict the movement of invasive organisms through national-and global-scale commercial trade networks (Harwood et al 2010;Kaluza et al 2010). A key feature of the network-based approach is that the physical distance between nodes is far less important than their level of connectivity (Moslonka-Lefebvre et al 2011); basically, the amount of movement along a vector between two nodes replaces the vector's length as the principal, or sometimes only, determinant of the likelihood of spread.…”

Managing tree pests and diseases in urban settings: The case of Oak Processionary Moth in London, 2006–2012

“…Hack 2010;Poland and McCollough 2006), these have tended to focus on the biological and epidemiological aspects of outbreaks, with few published studies focused on governance and management (though see Gustafsson and Lidskog, 2012 for an analysis of risk governance in relation to tree pest outbreaks). Exceptions in the UK include Dutch Elm Disease, which was the subject of a recent study examining outbreak management over a 40 year period (Tomlinson and Potter, 2010;Potter et al, 2011;Harwood et al, 2011), and the current and on-going outbreaks of Phytophthora ramorum and Phytophthora kernoviae in the UK, which has also been examined through a plant health governance lens Tomlinson et al, 2009). Other social science contributions have focussed on the legislative framework, policy protocols and risk assessment techniques surrounding the regulation of plant and tree pest and disease risks locally and globally (MacLeod et al, 2010;Mills et al, 2011;Outhwaite 2010).…”