Action: Cut/mow to control grass
- One controlled study in the UK found that mowing increased the number of heathland plants in one of two sites. The same study found that the presence of a small minority of heathland plants increased, but the presence of non-heathland plants did not change. Three replicated, controlled studies in the UK and the USA found that cutting to control grass did not alter cover of common heather or shrub seedling abundance.
- One replicated, controlled study in the UK found that cutting to control purple moor grass reduced vegetation height, had mixed effects on purple moor grass cover and the number of plant species, and did not alter cover of common heather.
- Two randomized, controlled studies in the USA found that mowing did not increase the cover of native forb species. Both studies found that mowing reduced grass cover but in one of these studies grass cover recovered over time. One replicated, controlled study in the UK found that mowing did not alter the abundance of wavy hair grass relative to rotovating or cutting turf.
Mowing involves cutting all vegetation in a shrubland. Doing this may allow shrubland species to become established at sites dominated by grasses.
Supporting evidence from individual studies
A controlled study in 1983–1989 in two heathlands that had been converted to grasslands in Dorset, UK (Smith et al. 1991) found that mowing increased the number of heathland plant species in one of two cases, increased the presence of heathland plant species in one of sixteen cases, and did not alter the presence of non-heathland plant species. After six years, areas that were mown had a higher number of heathland plant species (6 species) than areas that had not been mown (5 species). However, heathland plant species only had a higher presence in mown plots (present in 55% of plots) than in unmown plots (11%) in one of sixteen comparisons. The presence of non-heathland species did not differ significantly between mown plots (present in 0–86% of plots) and unmown plots (present in 0-64% of plots). In 1983 five 25 m2 plots were mown and five plots were left unmown. In 1989 four 1 m2 quadrats divided into twenty-five 20 x 20 cm squares were placed in each plot and the presence of plant species in each square recorded.
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 cutting invasive grasses did not increase the seedling abundance of seven of seven shrub species but did reduce grass cover. After one year, the number of shrub seedlings in areas where grasses were cut did not differ from that of areas where cutting was not carried out (0 seedlings/m2). Grass cover in areas where invasive grasses were cut was lower (15%) than areas where invasive grasses were not cut (84%). In 1997-1998 all grass was removed by hand from five randomly located 5 x 5 m plots, while in five other plots no grass was removed. 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.
A replicated, controlled study in 1996–1998 in a heathland invaded by wavy hair-grass Deschampsia flexuosa in Breckland, UK (Britton et al. 2000) found that mowing did not decrease the presence of wavy-hair grass or increase the presence of heather Calluna vulgaris relative to rotovating or cutting turf. After two years, wavy hair-grass presence in plots that had been mown (100% of plots) was not significantly different to presence in rotovated plots (99% of plots) or plots where turf had been cut (98% of plots). Heather presence did not differ significantly between plots that had been mown (5%) and those that had been rotovated (10%) or where turf was cut (24%). In August 1996 grass was cut to a height of 10 cm or less in 1–2 ha blocks, several 0.5 ha areas were rotovated, and in five 4 m2 turf and soil were removed to a depth of 10 cm. Five 4 m2 plots were established in each of the areas subject to different interventions. Each plot was divided into a grid of 20 x 20 cm squares and species presence was recorded in each square twice a year in 1996–1998.
A randomized, controlled study in 1999–2004 in sage scrub habitat in California, USA (Cox & Allen 2008) found that mowing to control invasive grass species had no effect on native forb cover and while it initially reduced the cover of invasive grasses, this subsequently increased. One year after mowing, cover of native forbs did not differ from mown and unmown plots (1%) and after five years cover was still not significantly different between mown (5%) and unmown plots (3%). Two years after mowing, mown plots had lower cover of invasive grass species (12%) than unmown plots (18%). However, after five years, cover of invasive grasses increased in mown plots (23%) and was not significantly different to that found in unmown plots (33%). Twenty 1 m2 plots were mown annually in 1999-2001, while twenty other plots were not mown. Plant cover in the plots was assessed annually in 2000-2004.
A randomized, replicated, controlled study in 1995–1999 at a moorland site in the UK (Milligan et al. 2004) found that cutting to control purple moor grass Molinia caerulea initially reduced vegetation height, had mixed effects on the number of plant species and cover of purple moor grass, and had no effect on the cover of common heather Calluna vulgaris. After eight months and in three of three cases, areas that were cut had shorter vegetation (8-21 cm) than areas that were not cut (26 cm), but after 44 months vegetation was only shorter in one of three cases (cut: 17 cm, uncut: 31 cm). After eight months and in one of three cases, cut areas had lower purple moor grass cover than areas that were not cut and after 44 months areas that were cut showed no significant difference in cover of purple moor grass when compared to uncut areas (no data presented). After 44 months in one of three cases areas that were cut contained more plant species (9 species) than areas that were not cut (6 species). The cover of common heather did not differ significantly between areas that were cut and those that were not. 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 June–August of 1996–1999 the plant species cover and vegetation height were surveyed using forty-eight 1 m2 quadrats placed in each plot.
- Smith R.E.N., Webb N.R. & Clarke R.T. (1991) The establishment of heathland on old fields in Dorset, England. Biological Conservation, 57, 221-234
- Cione N.K., Padgett P.E. & Allen E.B. (2002) Restoration of a Native Shrubland Impacted by Exotic Grasses, Frequent Fire, and Nitrogen Deposition in Southern California. Restoration Ecology, 10, 376-384
- Britton A.J., Marrs R.H., Carey P.D. & Pakeman R.J. (2000) Comparison of techniques to increase Calluna vulgaris cover on heathland invaded by grasses in Breckland, south east England. Biological Conservation, 95, 227-232
- Cox R.D. & Allen E.B. (2008) Stability of exotic annual grasses following restoration efforts in southern California coastal sage scrub. Journal of Applied Ecology, 45, 495-504
- Milligan A., Putwain P., Cox E., Ghorbani J., Le D.M. & Marrs R. (2004) Developing an integrated land management strategy for the restoration of moorland vegetation on Molinia caerulea-dominated vegetation for conservation purposes in upland Britain. Biological Conservation, 119, 371-385