RESTORATION EVIDENCE

Action: Use herbicide to control bracken Shrubland and Heathland Conservation

Key messages

Read our guidance on Key messages before continuing

Supporting evidence from individual studies

1 

A controlled, before-and-after trial between 1980 and 1982 in a heathland in Suffolk, UK (Marrs 1985) found that the application of herbicide reduced abundance of bracken Pteridium aquilinum and increased the number of heather Calluna vulgaris and silver birch Betula pendula seedlings. After two years, the number of heather seedlings and silver birch seedlings was higher in plots that had been treated with Krenite (heather: 44; silver birch: 9) than in untreated plots (heather: 11; silver birch: 1). The number of fern fronds in plots treated with the herbicide Krenite (476 fronds/plots) was lower than in untreated plots (731 fronds/plot), but higher than pre-treatment levels (325 fronds/plot). Four areas were selected for study on the heathland. Each area was divided into four 5 m x 10 m plots which were either treated with the herbicide Krenite, the herbicide 2,4,5-T, both Krenite and 2,4,5-T or left untreated. The numbers of heather fronts and colonising heather seedlings in plots was monitored annually between 1980 and 1982.

2 

A randomized, controlled study in 1978–1990 in a heathland in Suffolk, UK (Lowday & Marrs 1992) found that application of herbicide reduced the biomass of bracken Pteridium aquilinum, and increased heather biomass. After 12 years, biomass of bracken was 76–85% lower in areas where bracken had been sprayed with herbicide, than in unsprayed areas. Heather vegetation biomass was higher in areas that were sprayed with herbicide than in areas that were not sprayed (data presented in log units). In 1978 twelve 18 m2 plots were established. In four plots bracken was sprayed with the herbicide asulam in 1978, four plots were sprayed with asulam in 1978 and 1979, and in four plots were not sprayed. Vegetation cover was assessed every year in three 1 m2 plots which were randomly located in each plot. Heath vegetation was cut in 20 cm x 20 cm areas in each quadrat and dried to allow biomass to be calculated.

3 

A randomized, controlled study in 1978–1996 in heathland invaded by bracken Pteridium aquilinum in Suffolk, UK (Marrs et al. 1998) found that spraying with herbicide did not increase heather Calluna vulgaris cover, but did increase cover of wavy hair-grass Deschampsia flexuosa and sheep’s fescue Festuca ovina. After 10 years and in two of four cases, heather cover was higher in areas where bracken was sprayed with herbicide (22–28%) than in unsprayed areas (0%), but after 18 years the cover of heather in all plots declined to 0%. After 18 years, cover of wavy-hair grass and sheep’s fescue was higher in one of four cases where bracken was sprayed (wavy hair-grass: 9%; sheep’s fescue: 17%) than where it was not (wavy hair-grass: 0%; sheep’s fescue: 0%). In 1978 twelve 70 m2 plots were established. In 1978-1996 bracken was sprayed with asulam in eight plots, and four other plots were not sprayed. The vegetation cover in three quadrats/plot was surveyed every year in 1978-1996.

4 

A controlled study in 2002–2007 in a heathland in Exmoor, UK (Brook et al. 2007) found that using herbicide to control bracken Pteridium aquilinum increased the cover of gorse Ulex europaeus and the abundance of common cow-wheat Melampyrum pratense, but did not decrease the abundance of bracken. After five years, gorse cover was higher in areas treated with herbicide (42%) than in untreated areas (21%). There were more cow-wheat plants in plots treated with herbicide (0.7) than in untreated plots (0.4). Additionally, after five years, bracken abundance in plots that had been treated with herbicide (5) was not significantly different to that in untreated plots (7). In 2002 the herbicide asulox was applied in six 40 m x 20 m with a further six plots remaining unsprayed. Abundance and cover of plants was recorded in 30 randomly placed quadrats in each plot.

5 

A replicated, randomized, controlled study in 1993–2003 in three heathland sites in Cannock and the Peak District, UK (Alday et al. 2013) found that spraying bracken Pteridium aquilinum with the herbicide asulam increased heathland species richness. In plots where asulam was applied, species richness was higher ten years after herbicide spraying (4.9–7.6) than one year after spraying (4.5–7.1). However, over the same period species richness decreased in unsprayed plots (one year after: 3.2–4.9; 10 years after: 2.6–3.9) (data presented as model results). Ten years after treatment, species composition in sprayed and unsprayed plots did not differ significantly from unsprayed plots (data presented as ordination results). Between four and twelve 10 x 12 m and 10 x 5 m plots were selected and the herbicide asulam was sprayed in August 2003. Vegetation was monitored annually in June using 1 x 1 m quadrats.

6 

A randomized, replicated, controlled, paired study in 1993-1995 at a heathland site in Suffolk, UK (Paterson et al. 2000) found that using herbicide to control bracken Pteridium aquilinum reduced bracken cover, but had no significant effect on the cover of seven other plant species. In two of two cases bracken cover in areas where herbicide was sprayed (16-47%) was lower than in areas that were not sprayed (4-12%). The cover of the following plants did not differ significantly in sprayed and unsprayed areas: common heather Calluna vulgaris (sprayed: 0%, unsprayed: 0%), sedge species Carex spp. (sprayed: 0-1%, unsprayed: 1-7%), wavy-hair grass Deschampsia flexuosa (sprayed: 0-12%, unsprayed: 0-4%), sheep’s fescue Festuca ovina (sprayed:0% , unsprayed: 0-5%), Yorkshire fog Holcus lanatus (sprayed: 0%, unsprayed: 0%), sheep’s sorrel Rumex acetosella (sprayed: 1%, unsprayed:3-5%), and woodland ragwort Senecio sylvaticus (sprayed: 0%, unsprayed: 0%). In 1993 three 8 x 8m plots were sprayed with the herbicide asulam, and three plots were not cut. In July 1994 and 1995 plant cover was assessed in two 1 m2 quadrats placed in each plot.

7 

A replicated, randomized, controlled, paired study in 1992-1995 in a former heathland invaded by bracken Pteridium aquilinum in the Wirral, UK (Snow & Marrs 1997) found that spraying with herbicide to reduce the cover of bracken did not increase the number of common heather Calluna vulgaris seedlings relative to cutting. In eight of eight cases plots that were sprayed with herbicide did not have a significantly higher number of common heather seedlings than plots that were cut (herbicide: 8-20 seedlings/m2, cut: 1-76 seedlings/m2). Three 15 x 5 m plots were cut once a year, three plots were cut twice a year, and three plots were sprayed with the herbicide asulam. Cover of plants was assessed in three 1m2 quadrats in each plot in September 1993 and June 1994.

8 

A randomized, replicated, controlled, before-and-after, paired study in 2005–2013 in a site dominated by bracken Pteridium aquilinum in the UK (Milligan et al. 2016) found that spraying with herbicide reduced bracken cover and had no effect on the number of plant species or plant diversity. In plots that were sprayed with herbicide bracken cover declined over eight years (before: 26%, after: 2%) while in unsprayed plots bracken cover increased (before: 24%, after 75%). Neither the number of plant species (no data presented) nor plant diversity (presented as Shannon-Weiner index) differed significantly between sprayed and unsprayed plots. In 2005 three 20 x 20 m plots were sprayed with the herbicide asulam and every emergent bracken frond was sprayed in 2006–2012. Three other plots were not sprayed. Plots were paired. In 2005–2013 plant cover was assessed by eye in five 1 m2 quadrats which were randomly located in each plot.

Referenced papers

Please cite as:

Martin P.A., Rocha R., Smith R.K. & Sutherland W.J. (2018) Shrubland and Heathland Conservation. Pages 447-494 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.