Invasive Species
and the Railway By Neil Strong, Vegetation Specialist, Network Rail
Definition What is an invasive species? Toggling Shift f7 within a well known word processing package provides a handy pop-up thesaurus and for ‘invasive’, a few of the suggested alternatives are ‘persistent’ and ‘omnipresent’. As far as some existing Network Rail documents are concerned, the terms ‘injurious’ and ‘pernicious’ also feature, conjuring up visions of John Wyndham’s triffids stalking their way across the British countryside.
Whatever definition is used, there is no doubt that there are species resident in Britain that can affect normal working practices and have far reaching environmental and economic impacts. Many people will be well aware of the ultimate of triffids, giant hogweed and Japanese knotweed, both listed in the Wildlife & Countryside Act 1981 (as amended) for almost thirty years, but recent amendments may not be as familiar to many and the inclusion of well known garden plants like Cotoneaster and Crocosmia may be a surprise to some. It is not just the plants that are listed in the legislation that provide management issues on the railway infrastructure; many introduced (naturalised?) species also require intensive control to reduce the impact on safe and reliable operations. Furthermore, when does invasive have to relate to non-native plant species – the native species can be as much of an issue, and ones with legs…
The rail industry has, for many years, suffered the ridicule of the national press during the autumn months when deciduous trees shed their leaves. This article is not going to be providing a list of excuses of the ‘wrong sort of weed’ and besides, can a few hundred tonnes of locomotive really be affected by a plant? It is not so much the species affecting the railway, but the role the railway has to play in the management of its land and the impact that management can have on the environment and biodiversity of the land through which it passes.
Network Rail owns and manages in the region of 40,000 hectares of land within 20,000 miles of boundary. There are over 200 Sites of Special Scientific Interest on Network Rail property and our land holding passes through every National Park, most Areas of Outstanding Natural Beauty and through or near to countless SACs, Ramsars, SINCs, CAs, NNRs and SPAs… basically if it has an acronym, then we have the potential to affect it. Not only can the management practices affect the neighbouring biodiversity, but the railway can often be
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implicated in the actual spread of the organism itself, for example Oxford ragwort.
Railway vegetation management Trains on the domestic main lines travel up to 125mph on two steel rails held to sleepers supported in a layer of ballast. Either side of this ballasted area is a lineside, on average 12 metres wide, supporting a wide range of habitats and biodiversity all requiring timely and effective management to reduce the impact of any encroachment.
Everybody’s time is important and trains are expected to, and rightly should, run to schedule and vegetation is one of many factors that can influence the running of the railway, for instance through signalling issues during the autumn leaf fall period or whole trees blown over in winter storms. In order to reduce the impact of the vegetation, internal standards draw upon land management good practice to create a structure of vegetation on railway property that not only delivers our timetable promise, but also creates the potential for habitats that can exist alongside a 21st Century transport infrastructure. In addition, with 25,000 trains per day and well over a billion passenger journeys per year that lineside is the ‘shop window’ by which we are judged by all those looking out at it, and for that matter those 5 million or so neighbours looking in.
Starting at the middle, the ballasted area is a free draining substrate (defined as a ‘hard surface’ when using herbicides) and is essential in the track system as a whole. It has a propensity to collect organic material, wind or gravity-borne, and the natural processes of degradation can create ideal habitat for seed germination of pioneer species. Natural succession then takes over and it is possible to see, especially on some redundant track beds and disused lines the full gamete from pioneering weeds through to oak climax woodland! Not only does the ballast support the track, but this area
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