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Providing evidence to improve practice

Action: Use herbicide to control grass Shrubland and Heathland Conservation

Key messages

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  • Two randomized, controlled studies in the UK and the USA found that spraying with herbicide did not affect the number of shrub or heathland plant seedlings. One of these studies found that applying herbicide increased the abundance of one of four heathland plants, but reduced the abundance of one heathland species. However, one randomized, controlled study in the UK found that applying herbicide increased cover of heathland species. One randomized, replicated, controlled study in the UK reported no effect on the cover of common heather. One randomized, replicated study in the UK reported mixed effects of herbicide application on shrub cover.
  • Two randomized, controlled studies in the USA and the UK found that herbicide application did not change the cover of forb species. However, one randomized, controlled, study in the USA found that herbicide application increased native forb cover.
  • Four of five controlled studies (two of which were replicated) in the USA found that grass cover or non-native grass cover were lower in areas where herbicides were used to control grass than areas were herbicide was not used. Two randomized, replicated, controlled studies in the UK found that herbicide reduced cover of purple moor grass, but not cover of three grass/reed species. Two randomized, controlled studies in the UK found that herbicide application did not reduce grass cover.

Supporting evidence from individual studies

1 

A randomized, controlled study in 1988–1993 in former heathland in Dorset, UK (Pywell et al. 1995) found that spraying grass with herbicide did not change the number of seedlings of heathland species after one year but after three years it reduced the abundance of one of four heathland plant species and increased the abundance of one of four heathland plant species. After one year and for seven of seven heathland species, the number of seedlings in plots sprayed with herbicide (0–0.1 seedlings/m2) did not differ significantly from plots that were not sprayed with herbicide (0–0.2 seedlings/m2). After three years, the abundance of one of four heathland plant species was higher in plots that had been sprayed with herbicide (0.8 plants/m2) compared to plots that were not sprayed (0.4 plants/m2). However, the abundance of one of four heathland plant species was lower in plots that had been sprayed with herbicide (0.7 plants/m2) than in plots that had not been sprayed with herbicide (3.2 plants/m2). In 1989 glyphosate herbicide was sprayed on three 500 m2 plots at a rate of 5 litres/ha and three plots were left unsprayed. In 1990–1991 the number of seedlings was recorded in seven 0.5 m x 1 m quadrats which were placed in each plot. In 1993 the number of plant shoots was recorded in three 1 m2 quadrats which were randomly placed in each plot.

2 

A randomized, controlled study in 1997–1999 in sagebrush scrub habitat that had been invaded by grass and burnt by wildfires in California, USA (Cione et al. 2002) found that spraying invasive grasses with herbicide did not increase the seedling abundance of seven of seven shrub species but did reduce invasive grass cover. After one year, the number of seedlings of seven shrub species did not differ between areas sprayed with herbicide and unsprayed areas (sprayed: 0 seedlings/m2; unsprayed: 0 seedlings/m2).  Grass cover in areas where invasive grasses were sprayed with herbicide was lower (4%) than areas where invasive grasses were not sprayed (84%). In 1997–1998 grass was sprayed with the grass-specific herbicide Fusilade in five randomly located 5 x 5 m plots, while in five other plots no herbicide was used. In spring 1997 plots were surveyed for grasses using two 0.25 x 0.5 m quadrats/plot and two 0.5 x 1 m quadrats/plot for shrubs.

3 

A randomized, replicated, controlled study in 1996–1999 in moorland in the UK (Milligan et al. 2003) found that herbicide application to control grass initially reduced cover of purple moor grass Molinia caerulea and had no effect on cover of wavy-hair grass Deschampsia flexuosa, heath bedstraw Galium saxatile, and heath rush Juncus squarosus. After one year, cover of purple moor grass was lower in plots that had been sprayed with herbicide (29–45%) than in unsprayed plots (59%). After four years and in one of five comparisons, cover of purple moor grass was lower in plots sprayed with herbicide (35%) than in unsprayed plots (54%), but in four of five comparisons there was no difference in cover of purple moor grass (herbicide: 48-53%, no herbicide: 54%). The cover of wavy-hair grass, heath bedstraw, and heath rush did not differ significantly between plots sprayed with herbicide and unsprayed plots. Three blocks were established at the site, and divided into 12 plots, 11 of which were sprayed with different herbicides and one of which was left unsprayed. Cover of plant species was estimated using 1 m2 quadrats in August 1996, August 1997, and July 1999.

4 

A randomized, replicated, controlled study in 1995–2000 in four moorland sites in the UK (Marrs et al. 2004) found that applying herbicide reduced the cover of purple moor grass Molinia caerulea as well as cover of the three plant species, increased the cover of four plant species, and had mixed effects on the cover of six other plant species. In five of five years, areas where herbicide was used had a lower cover of purple moor grass (9-32%) than areas where herbicide was not applied (40-45%). The cover of common heather Calluna vulgaris, crowberry Empetrum nigrum, bilberry Vaccinium myrtillus was lower in areas where herbicide was applied than in areas where it was not applied (no data reported). The cover of cross-leaved heath Erica tetralix, Juncus squarrosus, Polytrichum commune, sphagnum spp. was higher in areas where herbicide was applied than in areas where it was not applied (no data reported). Application of herbicide had an inconsistent effect on the cover of sweet vernal grass Anthoxanthum odouratum, wavy-hair grass Deschampsia flexuosa, common cottongrass Eriophorum angustifolium, Eriophorum vaginatum, deergrass Trichophorum cespitosum and bog cranberry Vaccinium oxycoccus (no data reported). In 1995 two blocks were established on each site and half of each block was burned. Fencing was established to limit grazing in two plots within each burned area but one plot was left unfenced. Within each plot glyphosate herbicide was applied in two subplots and one subplot was not sprayed. Cover of each species was estimated in four 1 m2 quadrats which were randomly placed in each plot.

5 

A randomized, controlled study in 1999–2004 in sage scrub habitat in California, USA (Cox & Allen 2008) found that using grass-specific herbicide to control invasive grass species reduced the cover of invasive grasses but had no effect on native forb cover. After one year, areas where herbicide was applied had lower cover of invasive grass species (37%) than areas where no herbicide was applied (52%). After five years, cover of invasive grasses in herbicide treated areas (12%) was still lower than in areas not treated with herbicide (31%). After one year, cover of native forbs was not significantly different in areas where herbicide had been sprayed (4%) and in unsprayed areas (2%), but was higher in sprayed plots in one of five subsequent years (sprayed: 0–32% cover; unsprayed: 1–39% cover). Twenty 1 m2 plots were sprayed with the herbicide Fusilade II in 1999 and 2000, while twenty other plots were not sprayed. Plant cover in the plots was assessed annually in 1999–2004.

6 

A randomized, replicated, controlled, paired site study in 2005–2008 in creosote bush shrubland that was invaded by non-native grasses in California, USA (Steers & Allen 2010) found that spraying with herbicide reduced the cover of non-native grasses in four of four cases, increased the number of annual plant species in two of four cases and increased cover of native grass and forb species in three of four cases. In four of four cases, areas sprayed with herbicide had lower non-native grass cover (0–27%) than areas where no herbicide was sprayed (40–65%). In two of four cases, areas where herbicide had been sprayed had more annual plant species (7 species/plot) than areas that had not been sprayed (4–5 species/plot). In three of four cases where herbicide was sprayed cover of native grass and forb species was higher (58–89% cover) than areas where no herbicide was sprayed (22–37% cover). In January 2006 and 2008 twelve 8 x 8 m plots were sprayed with the grass specific herbicide Fusilade-II while in twelve other plots herbicide was not sprayed. Plant cover was recorded in March-April 2006 and 2008 in 0.5 m2 quadrats located in each plot.

7 

A randomized, controlled study in 1988–2005 in former heathland in Dorset, UK (Pywell et al. 2011) found that spraying grass with herbicide increased the cover of heathland species, but did not reduce the cover of grasses or forbs. After 17 years, the cover of heathland species was higher in plots sprayed with herbicide (45%) than in unsprayed plots (16%). There was no significant difference in the cover of grasses or forbs in plots sprayed with herbicide (grasses: 36%, forbs: 54%) and unsprayed plots (grasses: 59%, forbs: 27%). In 1989 glyphosate herbicide was sprayed on three 500 m2 plots and three plots were not sprayed with herbicide. In 2005 the cover of plants was recorded in four 1 m2 quadrats which were randomly placed in each plot.

8 

A randomized, replicated, controlled study in 1995-1999 at a moorland site in the UK (Milligan et al. 2005) found that applying herbicide to control purple moor grass Molinia caerulea had a mixed effect on vegetation height, and did not significantly alter the number of plant species, cover purple moor grass, or cover of common heather Calluna vulgaris. In one of four comparisons areas where herbicide had been applied had shorter vegetation (15 cm) than areas where herbicide was not applied (19 cm), in three of four cases there was no significant difference in vegetation height. There was no significant difference in the cover of purple moor grass or common heather, or the number of plant species in areas where herbicide was applied and areas where herbicide was not applied (no data presented). In December 1995 two blocks were established at the site. Each block was divided into four plots, one of which was cut once, one of which was cut twice, one of which was cut three times, and one of which was left uncut. In a sub-plot within each plot the herbicide quizalofop-ethyl was applied. In June–August of 1996–1999 the plant species cover and vegetation height were surveyed using forty-eight 1 m2 quadrats placed in each plot.

9 

A replicated, controlled study in 2008–2011 in two sagebrush steppe sites in California, USA (Kyser et al. 2013) that had been invaded by non-native grasses found that spraying with herbicide reduced cover of non-native grasses in the majority of cases, but did not alter cover of perennial grasses. In four of six cases cover of the non-native grasses medusahead Taeniatherum caput-medusae and downy brome Bromus tectorum was lower in areas sprayed with herbicide (0–6%) than in unsprayed areas  (2–52%) and in two cases there was no significant difference (sprayed: 0–1%, unsprayed: 0–1%). Cover of perennial grasses did not differ significantly between areas that had been sprayed with herbicide (3–12%) and unsprayed areas (4–6%). Twenty 30 x 30 m plots were established at two sites, 16 were sprayed with herbicides in October 2008, while four other plots were not sprayed with herbicide. Shrubland seed was sown in all plots in September 2009. Plots were surveyed in June 2009–2001 by randomly placing between five and 15 quadrats in each plot.

Referenced papers

Please cite as:

Martin P.A., Rocha R., Smith R.K. & Sutherland W.J. (2019) Shrubland and Heathland Conservation. Pages 493-538 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.