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What Works in Conservation 2018

 | 
William J. Sutherland
, 
Lynn V. Dicks
, 
Nancy Ockendon
, 
et al.

8. Shrubland and heathland conservation

8.8. Threat: Invasive and other problematic species

Texte intégral

8.8.1 Problematic tree species

Unknown effectiveness (limited evidence)

● Apply herbicide to trees

1One replicated, controlled, before-and-after study in South Africa found that using herbicide to control trees increased plant diversity but did not increase shrub cover. One randomized, replicated, controlled study in the UK found that herbicide treatment of trees increased the abundance of common heather seedlings. Assessment: unknown effectiveness (effectiveness 40%; certainty 35%; harms 10%).

2https://www.conservationevidence.com/​actions/​1629

● Cut trees

3One randomized, replicated, controlled study in the UK found that cutting birch trees increased density of heather seedlings but not that of mature common heather plants. One replicated, controlled study in South Africa found that cutting non-native trees increased herbaceous plant cover but did not increase cover of native woody plants. One site comparison study in South Africa found that cutting non-native Acacia trees reduced shrub and tree cover. Assessment: unknown effectiveness (effectiveness 37%; certainty 30%; harms 3%).

4https://www.conservationevidence.com/​actions/​1630

● Cut trees and remove leaf litter

5One before-and-after trial in the Netherlands found that cutting trees and removing the litter layer increased the cover of two heather species and of three grass species. Assessment: unknown effectiveness (effectiveness 45%; certainty 10%; harms 3%).

6https://www.conservationevidence.com/​actions/​1631

● Cut trees and remove seedlings

7A controlled, before-and-after study in South Africa found that cutting orange wattle trees and removing seedlings of the same species increased plant diversity and shrub cover. Assessment: unknown effectiveness (effectiveness 62%; certainty 20%; harms 0%).

8https://www.conservationevidence.com/​actions/​1632

● Use prescribed burning to control trees

9One randomized, replicated, controlled, before-and-after trial in the USA found that burning to control trees did not change cover of two of three grass species. One randomized, controlled study in Italy found that prescribed burning to control trees reduced cover of common heather, increased cover of purple moor grass, and had mixed effects on the basal area of trees. Assessment: unknown effectiveness (effectiveness 10%; certainty 20%; harms 22%).

10https://www.conservationevidence.com/​actions/​1721

● Use grazing to control trees

11One randomized, controlled, before-and-after study in Italy found that grazing to reduce tree cover reduced cover of common heather and the basal area of trees, but did not alter cover of purple moor grass. Assessment: unknown effectiveness (effectiveness 20%; certainty 10%; harms 5%).

12https://www.conservationevidence.com/​actions/​1634

● Cut trees and apply herbicide

13One controlled study in the UK found that cutting trees and applying herbicide increased the abundance of heather seedlings. However, one replicated, controlled study in the UK found that cutting silver birch trees and applying herbicide did not alter cover of common heather when compared to cutting alone. Two controlled studies (one of which was a before-and-after study) in South Africa found that cutting of trees and applying herbicide did not increase shrub cover. Two controlled studies in South Africa found that cutting trees and applying herbicide increased the total number of plant species and plant diversity. One replicated, controlled study in the UK found that cutting and applying herbicide reduced cover of silver birch trees. Assessment: unknown effectiveness (effectiveness 45%; certainty 35%; harms 3%).

14https://www.conservationevidence.com/​actions/​1636

● Cut trees and use prescribed burning

15One replicated, before-and-after trial in the USA found that cutting western juniper trees and using prescribed burning increased the cover of herbaceous plants. One replicated, randomized, controlled, before-and-after trial in the USA found that cutting western juniper trees and using prescribed burning increased cover of herbaceous plants but had no effect on the cover of most shrubs. One controlled study in South Africa found that cutting followed by prescribed burning reduced the cover of woody plants but did not alter herbaceous cover. Assessment: unknown effectiveness (effectiveness 40%; certainty 35%; harms 5%).

16https://www.conservationevidence.com/​actions/​1637

● Increase number of livestock and use prescribed burning to control trees

17One randomized, controlled, before-and-after study in Italy found that using prescribed burning and grazing to reduce tree cover reduced the cover of common heather and the basal area of trees. However, it did not alter the cover of purple moor grass. Assessment: unknown effectiveness (effectiveness 2%; certainty 12%; harms 12%).

18https://www.conservationevidence.com/​actions/​1722

No evidence found (no assessment)

19We have captured no evidence for the following interventions:

  • Cut/mow shrubland to control trees
  • Cut trees and increase livestock numbers.

8.8.2 Problematic grass species

Unknown effectiveness (limited evidence)

● Cut/mow to control grass

20One 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. Assessment: unknown effectiveness (effectiveness 22%; certainty 35%; harms 5%).

21https://www.conservationevidence.com/​actions/​1638

● Cut/mow to control grass and sow seed of shrubland plants

22One randomized, replicated, controlled study in the USA found that the biomass of sagebrush plants in areas where grass was cut and seeds sown did not differ from areas where grass was not cut, but seeds were sown. One randomized controlled study in the USA found that cutting grass and sowing seeds increased shrub seedling abundance and reduced grass cover One randomized, replicated, controlled study in the USA found that sowing seeds and mowing did not change the cover of non-native plants or the number of native plant species. Assessment: unknown effectiveness (effectiveness 31%; certainty 20%; harms 0%).

23https://www.conservationevidence.com/​actions/​1639

● Rake to control grass

24A randomized, replicated, controlled, paired study in the USA found that cover of both invasive and native grasses, as well as forbs was lower in areas that were raked than in areas that were not raked, but that the number of annual plants species did not differ. Assessment: unknown effectiveness (effectiveness 30%; certainty 20%; harms 12%).

25https://www.conservationevidence.com/​actions/​1640

● Cut/mow and rotovate to control grass

26One controlled study in the UK found that mowing followed by rotovating increased the number of heathland plant species in one of two sites. The same study found that the presence of a minority of heathland and non-heathland species increased. Assessment: unknown effectiveness (effectiveness 22%; certainty 15%; harms 7%).

27https://www.conservationevidence.com/​actions/​1641

● Apply herbicide and sow seeds of shrubland plants to control grass

28One randomized, controlled study in the USA found that areas where herbicide was sprayed and seeds of shrubland species were sown had more shrub seedlings than areas that were not sprayed or sown with seeds. One randomized, replicated, controlled study in the USA found that spraying with herbicide and sowing seeds of shrubland species did not increase the cover of native plant species, but did increase the number of native plant species. One of two studies in the USA found that spraying with herbicide and sowing seeds of shrubland species reduced non-native grass cover. One study in the USA found that applying herbicide and sowing seeds of shrubland species did not reduce the cover of non-native grasses. Assessment: unknown effectiveness (effectiveness 35%; certainty 30%; harms 0%).

29https://www.conservationevidence.com/​actions/​1644

Apply herbicide and remove plants to control grass

30One randomized, replicated, controlled, paired study in the USA found that areas sprayed with herbicide and weeded to control non-native grass cover had higher cover of native grasses and forbs than areas that were not sprayed or weeded, but not a higher number of native plant species. The same study found that spraying with herbicide and weeding reduced non-native grass cover. Assessment: unknown effectiveness (effectiveness 42%; certainty 20%; harms 2%).

31https://www.conservationevidence.com/​actions/​1645

● Use grazing to control grass

32One replicated, controlled, before-and-after study in the Netherlands found that grazing to reduce grass cover had mixed effects on cover of common heather and cross-leaved heath. One replicated, controlled, before-and-after study in the Netherlands found that cover of wavy-hair grass increased and one before-and-after study in Spain found a reduction in grass height. Assessment: unknown effectiveness (effectiveness 32%; certainty 17%; harms 10%).

33https://www.conservationevidence.com/​actions/​1646

● Use precribed burning to control grass

34One replicated controlled, paired, before-and-after study in the UK found that prescribed burning to reduce the cover of purple moor grass, did not reduce its cover but did reduce the cover of common heather. One randomized, replicated, controlled study in the UK found that prescribed burning initially reduced vegetation height, but this recovered over time. Assessment: unknown effectiveness (effectiveness 0%; certainty 20%; harms 15%).

35https://www.conservationevidence.com/​actions/​1723

● Cut and use prescribed burning to control grass

36One randomized, replicated, controlled, paired, before-and-after study in the UK found that burning and cutting to reduce the cover of purple moor grass reduced cover of common heather but did not reduce cover of purple moor grass. Assessment: unknown effectiveness (effectiveness 0%; certainty 10%; harms 10%).

37https://www.conservationevidence.com/​actions/​1724

● Use herbicide and prescribed burning to control grass

38One randomized, replicated, controlled, paired, before-and-after study in the UK found that burning and applying herbicide to reduce the cover of purple moor grass reduced cover of common heather but did not reduce cover of purple moor grass. Assessment: unknown effectiveness (effectiveness 0%; certainty 10%; harms 20%).

39https://www.conservationevidence.com/​actions/​1725

● Strip turf to control grass

40One controlled study in the UK found that cutting and removing turf increased the number of heathland plants. The same study found that the presence of a small number of heathland plants increased, and that the presence of a small number of non-heathland plants decreased. One replicated, controlled study in the UK found that presence of heather was similar in areas where turf was cut and areas that were mown or rotovated. One replicated, controlled study in the UK found that the presence of wavy hair grass was similar in areas where turf was cut and those that were mown or rotovated. Assessment: unknown effectiveness (effectiveness 32%; certainty 25%; harms 2%).

41https://www.conservationevidence.com/​actions/​1647

● Rotovate to control grass

42One replicated, controlled study in the UK found that rotovating did not alter the presence of heather compared to mowing or cutting. The same study found that wavy hair grass presence was not altered by rotovating, relative to areas that were mown or cut. Assessment: unknown effectiveness (effectiveness 0%; certainty 5%; harms 0%).

43https://www.conservationevidence.com/​actions/​1648

● Add mulch to control grass

44One randomized, controlled study in the USA found that areas where mulch was used to control grass cover had a similar number of shrub seedlings to areas where mulch was not applied. The same study found that mulch application did not reduce grass cover. Assessment: unknown effectiveness (effectiveness 0%; certainty 10%; harms 0%).

45https://www.conservationevidence.com/​actions/​1649

● Add mulch to control grass and sow seed

46One randomized, controlled study in the USA found that adding mulch, followed by seeding with shrub seeds, increased the seedling abundance of one of seven shrub species but did not reduce grass cover. Assessment: unknown effectiveness (effectiveness 5%; certainty 7%; harms 0%).

47https://www.conservationevidence.com/​actions/​1650

● Cut/mow, rotovate and sow seeds to control grass

48One replicated, controlled study in the UK found that rotovating did not alter the presence of heather compared to mowing or cutting. The same study found that wavy hair grass presence was not altered by rotovating, relative to areas that were mown or cut. Assessment: unknown effectiveness (effectiveness 50%; certainty 12%; harms 1%).

49https://www.conservationevidence.com/​actions/​1651

Unlikely to be beneficial

● Use herbicide to control grass

50Two 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. Assessment: unlikely to be beneficial (effectiveness 32%; certainty 40%; harms 7%).

51https://www.conservationevidence.com/​actions/​1643

8.8.3 Bracken

Unknown effectiveness (limited evidence)

● Use herbicide to control bracken

52One controlled, before-and-after trial in the UK found that applying herbicide to control bracken increased the number of heather seedlings. However, two randomized, controlled studies in the UK found that spraying with herbicide did not increase heather cover. One randomized, controlled study in the UK found that applying herbicide to control bracken increased heather biomass. One replicated, randomized, controlled study in the UK found that the application of herbicide increased the number of plant species in a heathland site. However, one replicated, randomized, controlled study in the UK found that spraying bracken with herbicide had no effect on species richness or diversity. One randomized, controlled study in the UK found that applying herbicide to control bracken increased the cover of wavy hair-grass and sheep’s fescue. One controlled study in the UK found that applying herbicide to control bracken increased the cover of gorse and the abundance of common cow-wheat. One controlled, before-and-after trial in the UK found that the application of herbicide reduced the abundance of bracken but increased the number of silver birch seedlings. Three randomized, controlled studies in the UK found that the application of herbicide reduced the biomass or cover of bracken. However, one controlled study in the UK found that applying herbicide did not change the abundance of bracken. Assessment: unknown effectiveness (effectiveness 50%; certainty 35%; harms 10%).

53https://www.conservationevidence.com/​actions/​1652

● Cut to control bracken

54One randomized, controlled, before-and-after trial in Norway and one randomized, controlled study in the UK found that cutting bracken increased the cover or biomass of heather. However, two randomized, replicated, controlled studies in the UK found that cutting bracken did not increase heather cover or abundance of heather seedlings. One randomized, replicated, controlled study in the UK found that cutting to control bracken increased the species richness of heathland plant species. However, another randomized, replicated, controlled study in the UK found that cutting to control bracken did not alter species richness but did increase species diversity. One randomized, replicated, controlled study in the UK found that cutting bracken increased cover of wavy hair-grass and sheep’s fescue. One controlled study in the UK found that cutting bracken did not increase the abundance of gorse or common cow-wheat. One randomized, controlled, before-and-after trial in Norway and two randomized, controlled studies in the UK found that cutting bracken reduced bracken cover or biomass. One randomized, replicated, controlled, paired study the UK found that cutting had mixed effects on bracken cover. However, one controlled study in the UK found that cutting bracken did not decrease the abundance of bracken. Assessment: unknown effectiveness (effectiveness 50%; certainty 35%; harms 2%).

55https://www.conservationevidence.com/​actions/​1653

● Cut and apply herbicide to control bracken

56One randomized, controlled study in the UK found that cutting and applying herbicide to control bracken did not alter heather biomass. One randomized, controlled, before-and-after trial in Norway found that cutting and applying herbicide increased heather cover. One randomized, replicated, controlled, paired study in the UK found that cutting and using herbicide had no significant effect on the cover of seven plant species. One replicated, randomized, controlled study in the UK found that cutting bracken followed by applying herbicide increased plant species richness when compared with applying herbicide followed by cutting. Three randomized, controlled studies (one also a before-and-after trial, and one of which was a paired study) in the UK and Norway found that cutting and applying herbicide reduced bracken biomass or cover. Assessment: unknown effectiveness (effectiveness 30%; certainty 30%; harms 4%).

57https://www.conservationevidence.com/​actions/​1654

● Cut bracken and rotovate

58One controlled study in the UK found that cutting followed by rotovating to control bracken did not increase total plant biomass or biomass of heather. Assessment: unknown effectiveness (effectiveness 0%; certainty 10%; harms 0%).

59https://www.conservationevidence.com/​actions/​1656

● Use ‘bracken bruiser’ to control bracken

60One randomized, replicated, controlled, before-and-after, paired study in the UK found that bracken bruising increased bracken cover, though bracken cover also increased in areas where bracken bruising was not done. There was no effect on the number of plant species or plant diversity. Assessment: unknown effectiveness (effectiveness 0%; certainty 10%; harms 7%).

61https://www.conservationevidence.com/​actions/​1726

● Use herbicide and remove leaf litter to control bracken

62One randomized, controlled study in the UK found that using herbicide and removing leaf litter did not increase total plant biomass after eight years. The same study found that for three of six years, heather biomass was higher in areas where herbicide was sprayed and leaf litter was removed than in areas that were sprayed with herbicide. Assessment: unknown effectiveness (effectiveness 27%; certainty 12%; harms 2%).

63https://www.conservationevidence.com/​actions/​1660

No evidence found (no assessment)

64We have captured no evidence for the following interventions:

  • Cut and burn bracken
  • Use herbicide and sow seed of shrubland plants to control bracken
  • Increase grazing intensity to control bracken
  • Use herbicide and increase livestock numbers to control bracken.

8.8.4 Problematic animals

Unknown effectiveness (limited evidence)

● Use fences to exclude large herbivores

65One controlled study in the USA found that using fences to exclude deer increased the height of shrubs, but not shrub cover. Assessment: unknown effectiveness (effectiveness 7%; certainty 10%; harms 0%).

66https://www.conservationevidence.com/​actions/​1662

● Reduce numbers of large herbivores

67One before-and-after trial in the USA found that removing feral sheep, cattle and horses increased shrub cover and reduced grass cover. One replicated study in the UK found that reducing grazing pressure by red deer increased the cover and height of common heather. Assessment: unknown effectiveness (effectiveness 70%; certainty 30%; harms 0%).

68https://www.conservationevidence.com/​actions/​1663

No evidence found (no assessment)

69We have captured no evidence for the following interventions:

70• Use biological control to reduce the number of problematic invertebrates.

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