Corky-fruited Water-dropwort Oenanthe pimpinelloides in Suffolk: an update

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Suffolk Natural History, Vol. 52

CORKY-FRUITED WATER-DROPWORT OENANTHE PIMPINELLOIDES IN SUFFOLK: AN UPDATE FROM THE MAIN POPULATION AT BOURNE BRIDGE, IPSWICH TIM GARDINER & CHRIS STRACHAN Introduction The main location from which corky-fruited water-dropwort Oenanthe pimpinelloides is currently known in Suffolk is in the immediate surroundings of Bourne Bridge (grid ref: TM160419) where Belstead Brook flows into the Orwell Estuary. Despite being classified as of Least Concern in England’s Red Data List (Stroh et al. 2014), this tall growing perennial plant is listed as ‘rare (but common elsewhere)’ in the Suffolk Rare Plant Register (Sanford 2005). At Bourne Bridge, the plant is found on and around raised clay embankments which act as tidal flood defences next to a set of sluice gates. A track which runs from the road to the sluice has a large concentration of plants which benefit from annual mowing to allow access by vehicles and machinery. The grassy flood defence embankments are largely covered in scrub and trees. The plant is noted as occurring on neutral soils in dry pastures, hay meadows, roadside verges, and banks (Leach & Southam 1994). Despite its tall growing form, it can persist under quite intensive management on village playgrounds and football pitches. Its springy flower stems tend to escape mowing which may explain its abundance on the mown track at Bourne Bridge. Research suggests that gaps in the turf (bare earth) may also be important for seedling establishment; therefore, the track used by vehicles provides these opportunities in the sward. It is the aim of this short paper to provide an update on recent flood defence management of the site by the Environment Agency (EA) and efforts to conserve O. pimpinelloides at its most important Suffolk site. Effects of scrub clearance Management During February 2012, scrub and trees were cleared from the embankment using chainsaws and brushcutters to allow inspection of the structural integrity of the flood defence by EA engineers. Woody species such as ash Fraxinus excelsior, dog rose Rosa canina agg., hawthorn Crataegus monogyna and pedunculate oak Quercus robur were removed from the embankments. Survey method Annual surveys of O. pimpinelloides at the site were undertaken before and after the clearance works (once annually in September 2011-14 and once in early October 2015). Counts of the number of O. pimpinelloides seed heads were made in several distinct areas of the site including the boat store, grassy track verges and two scrub cleared embankments. The counts involved a general sweep of the area. These counts serve as an estimate of the total number of plants and are likely to be a significant underestimate due to the particularly high concentration of plants in some areas such as the boat store. Results are presented as the total number of seed heads counted in each area and as numbers per m2 (number of seed heads divided by size of each area in m2). Trans. Suffolk Nat. Soc. 52 (2016)


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