Securing Biodiversity in Breckland - European Commission

Shallow cultivation is preferable to deeper ploughing. Monitoring of experimental plots showed that“Shallow cultivation tended to result in higher cover of annuals and dicotyledonous species (in May)and lower Ellenberg N values, than deep cultivations. Continual shallow cultivation also resulted inincreases in the number of monocotyledonous species under most timing regimes, while number ofperennial species increased irrespective of either depth or timing” (ADAS 2001). This is furthersupported by evidence from Hillborough and Ickburgh in Breckland. Here, heavy harrowing to breakup surface soil but not invert it (as would occur in ploughing) has maintained a good balance of openground and vegetation over long time periods without the loss of open conditions to perennialgrasses (B. Nichols pers. comm.). This was despite the persistence of perennials in the vegetation.However, the role of light chalky soils in this result is perhaps also important.However irrespective of depth, repeated annual cultivation generally results in a gradual build up ofboth annual and perennial grasses (ADAS 2001) that over time reduce the abundance of desired openground, nectar sources and annual plant species and their associated seed production (e.g. for seedeatingbeetles). In contrast, evidence from the arable weed reserve at Weeting suggests thatcultivating a low intensity cereal crop prevents such a build-up of grass; this may be at least partlydue to dominance and shading of the vegetation by the cereal (although an additional importantfactor is the lack of inorganic fertiliser inputs to this field).However a simple and pragmatic solution to grass build-up is to occasionally spray with a broadspectrum herbicide late in the growing season and to then re-cultivate (Panter et al., 2010). This isnot a problem for the majority of desired annual plants; even if adults are sprayed off regenerationreadily occurs from a healthy seedbank replenished annually through the good growth and suitableabove ground conditions. Glyphosate has been shown to be non harmful to larger carabids. Howeversub-lethal effects have recently been reported for spiders (Benamú, Schneider and Sánchez 2010).The evidence base by which to assess the relative benefits of cultivated margins and unsprayedcereal margins appears incomplete and is strongly slanted towards vascular plants, with the relativebenefits of prescriptions to scarce invertebrates poorly known.Recommendation: Research should be conducted to examine whether annual cultivation of arable margins (e.g.as in cultivated margin prescriptions) or other ruderal habitats (e.g. recreated brecks withinForestry Landscape) gives similar outcomes to prescriptions or management with low densityunsprayed spring cereal crop. Effects should be studied on the plant and invertebrate speciespopulations and assemblages sustained and the seed bank densities achieved.Delivering ungrazed, disturbed conditions outside the arable landscapeTargeting large lightly or extensively grazed grass-heath complexesIn extensively grazed sites such as STANTA, rotovation or ploughing of very large areas may provide avolume of ruderal vegetation some of which would remain ungrazed. In other large heathland sites itmay be appropriate to fence off and plough areas outside of the grazing regime. Such large scalecultivations would serve two purposes: firstly rejuvenating now species-poor areas of grass-heath(through exposing buried seedbanks and nutrient depletion) and secondly by providing a temporaryflush of ruderal vegetation.167