I was first alerted to dieback of gorse (Ulex europeaus) at the Thames Basin Facilitation Fund Group that I jointly coordinate at the end of April. A number of the attending nature reserve managers had noticed that significant amounts of gorse on their land had become brown and dry.
I offered to set up an online recording form (https://forms.gle/Dc6Ubyy8aCWf8P7B7) to ensure that the scale and spread of the phenomenon was captured at an early stage.
Over 50 reports were received within a few weeks of launching the form, demonstrating the extent of the issue, and I have since witnessed the problem myself wherever gorse is present.
This map shows the location of the reports that I have received, with the colour of the points indicating the severity of the dieback. From observation and correspondence it is likely to be much more ubiquitous, but the map gives an indication of how widespread the issue is.
Gorse is a vital component of our natural habitats, especially lowland heath and moorland where it is home to many animals. It is a food plant for Green Hairstreak butterflies, for example, and its structure provides scaffolding for countless spiders. Dartford Warblers rely on dense gorse to overwinter in the UK, and Linnets feed on the seeds.
On receipt of so many reports, and my own observations from across Hampshire, Wiltshire and Berkshire, I took samples of dead and dying Gorse from Frensham Common to Dr Caroline Gorton at the Tree Health Diagnostic and Advisory Service at Forest Research, Alice Holt. Caroline had agreed to test for likely pathogens.
Three samples were tested - two whole bushes with roots and soil, and one cutting from a larger bush. All showed signs of dieback, but had some live tissue so that decay had not fully set in, and any pathogens would still be present.
The Forest Research team found no evidence of Xyella, a bacterium that is having a similar impact on other plants in Europe; and no evidence of Phytophthora a group of 'water moulds' that cause sudden oak death and other plant disease.
A limited amount of the pathogenic fungus Diaporthe was identified from the samples, but this was deemed unlikely to be the cause of such significant dieback.
The samples collected, and other plants observed in the field, were not fully dead, and retained some live tissue including regeneration from the base.
It is likely that these plants will regrow this year as if they had been coppiced.
In the short term the amount of dead material will create an increased wild fire risk, as dead gorse burns more readily than live gorse, and a loss of habitat for the host of wildlife that depends upon it, but, hopefully, in the long term it will recover and continue to flourish.
The cause of this phenomenon is not fully understood but the consensus is that it it is 'abiotic' - caused by an environmental factor rather than a disease. The rate of spread is not consistent with a disease or pest outbreak.
Instead, the prolonged and unusually cold weather experienced in late January and early February is deemed the most likely cause.
If we continue to experience more extreme weather due to climate change, then who knows what impact this will have on our wildlife. Gorse appears to be one of the hardier plants in the countryside, but I have been shocked at the extent and impact of this episode.
With thanks to Dr Caroline Gorton at the Tree Health Diagnostic and Advisory Service at Forest Research, Alice Holt; and Vicky Keller, Countryside Ranger at Waverley Borough Council.