Increasing biodiversity of flood meadow by overseeding

Background

When the trustees bought the neglected 7-hectare (18-acre) flood meadow in 1996, we were advised that a July hay cut and aftermath grazing, combined with regular flooding, would restore this ancient meadow.

 However, grazing by cattle has been hard to arrange since the foot-and-mouth epidemic, and there are few species-rich flood meadows upstream.  Consequently, wild flower biodiversity has, if anything, decreased and coarse grasses such as false oat (Arenatherum elatius) probably increased.

A pilot seeding project being undertaken by Dr John Metcalfe is proving very encouraging.  Preparing the soil by mowing, rotavating (or scarifying) and hand sowing yellow rattle at first, then a wild flower seed mix has produced a good crop of yellow rattle, so far.  This encouraged us to undertake overseeding three hectares starting on 6^th September 2006.

Plan

The plan was drawn up by Charles Flower of Flower Farms, Shalbourne, who was consultant to the project and supplied seed of local provenance, and Tim Way, Contracts Supervisor of White Horse Contractors Ltd of Abingdon.  John Sargent, Estate Manager of Northmoor Trust also gave very helpful advice.  He has slot seeded very successfully at Northmoor.  However, his meadow may have been more receptive than the Hurst and strip spraying of herbicide was also used.  The advice received was that rotavating was more likely to succeed than slot seeding, which tended to sow too deeply.  The contractor was prepared to be flexible and see which machine worked best on the day.

Four plots were measured and flagged on the four areas east of the public footpath, adding up to 3 ha (see map).

• Plot A. Middle field 1.56 hectares phosphate index 1 
• Plot B. Top field 0.70 hectare phosphate Index 2 
• Plot C. Between old drains 0.3 hectare phosphate index 2 
• Plot D. Strip by River Thame 0.44 hectares phosphate index 3

The work for 2006 is described below and has been completed.  A further flail cut and collection is planned for spring 2007 (subject to Defra consent) or grazing, followed by a similar programme of cutting, ground preparation and seeding in September 2007, but with 25% yellow rattle and 75% seed mix.  The programme may be modified in the light of what we have learned so far.  A further spring cut is planned for 2008, subject to Defra consent.  A botanical survey will be carried out in 2008 and regularly thereafter to see if we meet the success criteria for the Defra Higher Level Environmental Stewardship Scheme by 2011.

Timetable of work done

4/5 Sept 2006:  Close cut of flagged areas using an AGIP Tierre 250 flail cutter, followed by a second cut at 90° or 180° using a Wessex HTC18 flail cutter with collector.  The cuttings were dumped to rot down on thistle patches.  Half of plot A had an extra close cut.

6 Sept 2006:  The four areas were rotavated using a Greenland 400-70-1 power harrow.  The depth and speed were adjusted by Tim Way and Charles Flower to produce the optimum disturbance of the soil, leaving one third to one half of the soil bare.

The harrowed area was then sown using an 8-foot BLEC Turfmaker with a mix of 75% yellow rattle and 25% of a wild flower seed mix listed below.  A small area along the public footpath was seeded using a 4-foot BLEC Cultipak.

Calibration of the seeder was problematic, as the yellow rattle seed consisted of flat discs 5-10 mm in diameter, whereas the remainder of the mix was of very small seed.  If the slot was wide enough to let the yellow rattle pass, the wild flower seed flowed too freely.  The seeding rate was only 2.8 kg per hectare (0.28 g per m2) so it had been bulked out with sawdust (one part seed to three).  The solution was to bulk it out further with kiln-dried sand.

7 Sept:  All seeded areas were rolled using an 8-foot Cambridge roller. The total time taken was 3½ days, with two skilled and hard-working operators, plus about two days for Tim Way and one day for Charles Flower.  They worked closely together in solving problems in this area of great uncertainty. 

Cost 

The first year's costs are estimated at £4,990.  There was not enough time to apply for outside funding for the 2006 programme, so three trustees made personal donations to cover the cost  to avoid a year's delay. 

The subsequent costs are estimated at £8,447 and application has been made to the WREN (Waste Recycling Environmental Ltd) Gift Aid fund for this sum.  If this fails, we will apply to TOE (Trust for Oxfordshire's Environment) for funding under the Landfill Communities Fund.

Wild flower species sown

First year yellow rattle 75%: seed mix (see below) 25% (Second year 25%:75%).  All are on Defra list of high-value indicator species except those in brackets (FEP handbook p. 65).

Link to flora gallery

Link to reseeding project pictures