Fill/block ditches to create conditions suitable for peatland plants (without planting)

Overall effectiveness category Likely to be beneficial
Number of studies: 3
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How is the evidence assessed?

Effectiveness

60%
Certainty

50%
Harms

0%

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Background information and definitions

Many threats can contribute to the formation of ditches or channels in peatlands (Evans et al. 2005). Deep channels (gullies) may be eroded by humans or livestock repeatedly using set trails and/or by heavy rainfall events. Erosion can be increased by burning and acid rain. Ditches may be deliberately dug to drain peatlands for agriculture, forestry or mining. Peatland vegetation cannot establish in ditches that contain deep water or are regularly disturbed by flowing water.

This section considers growth of peatland vegetation within filled or blocked ditches. Ditches could be completely filled to immediately create a surface for plants to grow on. Alternatively, ditches could be blocked with dams: creating shallow pools, encouraging peat deposition and eventually creating new surfaces on which peatland plants can grow. This would mimic natural revegetation processes (Evans et al. 2005).

Key peatland types where this action may be appropriate: bogs, fens/fen meadows, tropical peat swamps.

Related action: rewetting larger areas of peatland, including by blocking ditches.

_{Evans M., Allott T., Crowe S. & Liddaman L. (2005) Feasible locations for gully blocking. Pages 27–76 in: M. Evans, T. Allott, J. Holden, C. Flitcroft & A. Bonn (eds.) Understanding Gully Blocking in Deep Peat. Moors for the Future Research Report 4.}

Study locations

Key messages

Three studies evaluated the effects of filling or blocking ditches (without planting) on peatland vegetation within them. Two studies were in bogs and one was in a fen.
Vegetation cover (3 studies): Two studies in a bog in the UK and a fen in the USA reported that blocked or filled ditches were colonized by herbs and bryophytes within 2–3 years. In the USA, vegetation cover (total, bryophyte, forb, grass and sedge) was restored to natural, undisturbed levels. One replicated study in bogs in the UK reported that plants had not colonized blocked gullies after six months.
Overall plant richness/diversity (1 study): One site comparison study in a fen in the USA found that a filled ditch contained more plant species than adjacent undisturbed fen, after two years.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated study in 2003–2004 in two degraded blanket bogs in England, UK (Evans et al. 2005) reported that gullies blocked with dams had no vegetation cover after approximately six months. In late 2003, 389 blockages were installed along 16 gullies. A mixture of blocking techniques was used: wooden fences, plastic fences, stone walls or stacked hessian sacks. Vegetation cover was visually estimated in May to July 2004.
Study and other actions tested
Referenced paper
Evans M., Allott T., Crowe S. & Liddaman L. (2005) Feasible locations for gully blocking. Pages 27-76 in: M. Evans, T. Allott, J. Holden, C. Flitcroft & A. Bonn (eds.) Understanding gully blocking in deep peat. Moors for the Future Research Report no.4, Moors for the Future.
A replicated study in 2006 in a blanket bog in England, UK (Armstrong et al. 2008) reported that drainage ditches blocked with peat developed some vegetation cover but were mostly bare peat. All five blocked drainage ditches developed some vegetation cover, although total vegetation cover was <50% in four of them. Across all five ditches, cover of common cottongrass Eriophorum angustifolium was 5–30%.Cover of Sphagnum moss was <1–20%. One ditch (also recently burned) had 60% cover of heather Calluna vulgaris. The study noted correlations between vegetation cover, slope and soil/water chemistry. In January 2003, five ditches were blocked with peat sods. Vegetation cover was estimated in spring 2006 (A. Armstrong pers. comm.).
Study and other actions tested
Referenced paper
Armstrong A., Holden J. & Stevens C. (2008) The differential response of vegetation to grip blocking. Report to North Pennines AONB report.
A site comparison study in 2009–2011 in a fen in Michigan, USA (Bess et al. 2014) found that a ditch filled with peat spoil developed similar vegetation cover to undisturbed areas of the fen, but contained more plant species. After two years, the filled ditch and adjacent areas of undisturbed fen had similar cover of total vegetation (165 vs 180%), sedges (81 vs 80%), grasses (15 vs 10%), forbs (33 vs 20%) and bryophytes (29 vs 40%). However, there were more plant species in the filled ditch (49 species) than undisturbed fen (40 species). Results after one year were similar, except that the ditch had lower total vegetation cover than undisturbed fen (126 vs 188%) and lower bryophyte cover (18 vs 40%). In 2009, a ditch (dug in 2007 as a fire break) was filled with adjacent spoil (still moist and containing fen plant seeds). In 2010 and 2011, vegetation cover was recorded in sixty 1 m² quadrats along the length of the ditch: 20 within it and 20 on either side. These were placed in areas not sown with additional seeds.
Study and other actions tested
Referenced paper
Bess J.A., Chimner R.A. & Kangas L.C. (2014) Ditch restoration in a large Northern Michigan fen: vegetation response and basic porewater chemistry. Ecological Restoration, 32, 260-274.

Please cite as:

Taylor, N.G., Grillas, P. & Sutherland, W.J. (2020) Peatland Conservation. Pages 367-430 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Peatland Conservation

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Actions	Effectiveness	Studies	Category
Introduce nurse plants (without planting peatland vegetation) Action Link	No evidence found (no assessment)	0	Synopsis Link
Cover peatland with something other than mulch (without planting) Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link
Directly plant peatland mosses Action Link	Likely to be beneficial	7	Synopsis Link