Long-term effectiveness of AES-funded bracken control

The report, commissioned by DEFRA/Natural England, investigates the effectiveness of bracken control, using remote sensing techniques to investigate the current impact of the AES in England.

A remote sensing methodology was developed by using optical satellite imagery from the Landsat-8 and Sentinel-2 platforms to evaluate changes to bracken cover from 2014 to 2020. The methodology devised measures to mitigate cloud cover, reducing the temporal frequency of data availability over the seven years evaluated and for a lack of spatial information on the exact extent of bracken options within parcels.

Interviews were conducted for 171 agreement holders and were designed to collect structured information about the effectiveness of the bracken control options and the long-term effectiveness of AES funded bracken control.

The report concluded that, from a final sample of 134 parcels, bracken cover had mostly reduced over the evaluation period and typically covered less than 30% of parcels by 2018-2020. Overall, these results suggest that the bracken control work is having a positive effect on reducing bracken cover for the parcels evaluated.

In addition, comparing the remote sensing findings against environmental factors, the results were strongly influenced by geographic clustering of results, but there was some indication that the rate of bracken growth may be affecting outcomes, with areas likely to support faster growth more strongly correlated with an increase in bracken cover between baseline and revisit assessments. Detailed case studies also demonstrated the importance of site- and agreement-specific variables for evaluating the success of bracken control measures.

Furthermore, interviews showed that a significant proportion of agreement holders had been managing bracken both within and outside AES agreement for a long time, and there is a sense that bracken management is becoming more challenging. The impacts of bracken are perceived as wide-ranging but centre on biodiversity and a loss of grazing land. Agreement holders feel that treatments need to be made repeatedly throughout the agreement, especially when using mechanical control measures. The interviews with agreement holders revealed a possible link between grazing and bracken control, but it was unclear that cattle were more effective than other livestock. Further research is needed to assess the effectiveness of different grazing regimes, timing and the type of livestock on bracken control. The issue of bracken control is complex and could be impacted by local factors, such as altitude or geology. It is clear that farmers and other agreement holders are innovative in their attempts to reduce the spread of bracken.

In conclusion, the report's findings suggested that several years of control are needed to reduce bracken cover within parcels, but given climate change and increased interest in rewilding, conditions are likely to favour extremely vigorous bracken growth in the future.