Data extracted in May 2022
Fiche created in December 2023

Note to the reader: This general fiche summarises all the environmental and climate impacts of PEATLAND CONSERVATION AND RESTORATION found in a review of 6 synthesis papers[1]. These papers were selected from an initial number of 471 obtained through a systematic literature search strategy, according to the inclusion criteria reported in section 4. The impacts reported here are those for which there is scientific evidence available in published synthesis papers, what does not preclude the farming practice to have other impacts on the environment and climate still not covered by primary studies or by synthesis papers.

The synthesis papers review a number of primary studies ranging from 41 to 96. Therefore, the assessment of impacts relies on a large number of results from the primary studies, obtained mainly in field conditions, or sometimes in lab experiments or from model simulations.

1.      DESCRIPTION OF THE FARMING PRACTICE

  • Description:
    • A peatland is a type of wetland with a naturally accumulated layer of peat at the surface due to organic matter production exceeding decomposition.[2]
    • Peatlands are generally classified as bogs and fens. Bogs are fed mainly by rain and snow, while fens develop in landscape depressions and are fed with surface and/or ground water. Other names referring to peatlands found in this review are swamp, and wet heath, though the search string included more synonyms (see section 4). Carbon-rich soils are included in this definition. These soils have an organic layer usually with >15 % of organic matter. However, the synthesis papers included in this review do not clearly define what they consider carbon-rich soils and thus we rely on their knowledge and criteria to include individual studies in their reviews.
    • This review includes interventions in peatlands related to:
    • Conservation refers to the preservation (i.e., no transformation to other land uses) of natural non-disturbed peatlands compared to either degraded or restored peatlands. The degraded peatlands found in this review are mainly affected by alterations in their water regime due to drainage and/or conversion to cropland or pasture. The restored peatlands found in this review have been subject to different interventions including the re-establishment of peatland vegetation, water supplementation or passive restoration by abandonment of agricultural use.
    • Restoration methods found in this review are classified into two main classes: management of water regime and a general class with several restoration methods pooled together. Restoration by managing water regime refers to re-allocating a part of the natural water regime back to these soils/ecosystems, resulting in the full or partial recovery of water inputs and inundation by removing draining, ditching, precipitation exclusion, flooding, dams or groundwater extraction. When different restoration methods are analysed together in the reviewed synthesis papers, we report them as several restoration methods pooled together. This pool includes active revegetation, full or partial recovery of water inputs and passive restoration by cessation of human disturbance (i.e., agricultural abandonment and prohibited grazing).
  • Key descriptors:
    • The estimation of peatland conservation impacts is based on the spatial comparison between preserved natural peatlands (intervention) and nearby degraded or restored peatlands (comparator).
    • The estimation of peatland restoration impacts is based on the spatial and temporal comparisons between restored peatlands (intervention) and degraded peatlands (comparator). Spatial comparisons are those conducted simultaneously between restored peatlands and nearby degraded peatlands. Temporal comparisons are those conducted in the same peatland before and after restoration.
    • This review does not include other management practicesconductedin peatlands such as burning, grazing, fertilisation, or low-intensity farming, which are assessed in separate sets of fiches (i.e., peatland management).

2.     EFFECTS OF THE FARMING PRACTICE ON CLIMATE AND ENVIRONMENTAL IMPACTS

We reviewed the impacts of the conservation of natural peatlands as compared to degraded peatlands or to restored peatlands, and the impacts of restoration of peatlands compared to degraded peatlands (Table 1). These comparisons are conducted after peatlands have been degraded or restored, therefore, the potential net emissions during those conversions are not considered in these comparisons.

The table below shows the number of synthesis papers with statistical tests reporting i) a significant difference between the Intervention and the Comparator, that is to say, a significant statistical effect, which can be positive or negative; or ii) a non-statistically significant difference between the Intervention and the Comparator. In addition, we include, if any, the number of synthesis papers reporting relevant results but without statistical test of the effects. Details on the quality assessment of the synthesis papers can be found in the methodology section of this WIKI.

All selected synthesis papers included studies conducted in Europe , and 6 have a quality score higher than 50%.

Table 1: Summary of effects. Number of synthesis papers reporting positive, negative or non-statistically significant effects on environmental and climate impacts. The number of synthesis papers reporting relevant results but without statistical test of the effects are also provided. When not all the synthesis papers reporting an effect are of high quality, the number of synthesis papers with a quality score of at least 50% is indicated in parentheses. Some synthesis papers may report effects for more than one impact, or more than one effect for the same impact.

 

 

 

 

Statistically tested

Non-statistically tested

Impact

Metric

Intervention

Comparator

 Significantly positive

Significantly negative

Non-significant

Increase Carbon sequestration

Soil organic carbon

Conservation of natural peatland

Degraded/altered wetland due to cultivation

1

0

0

0

Conservation of natural peatland

Restored peatland

0

0

1

0

Restoration of peatland

Degraded/altered peatland due to cultivation

1

0

0

0

Decrease GHG emissions

CH4 emissions

Conservation of natural peatland

Degraded/altered peatland due to conversion to pasture

0

0

1

0

Conservation of natural peatland

Degraded/altered peatland due to cultivation

0

0

1

0

Conservation of natural peatland

Drained peatland

0

2

1

0

Restoration by management of water regime

Drained peatland

0

2

1

0

Decrease GHG emissions

CO2 emissions

Conservation of natural peatland

Degraded/altered peatland due to conversion to pasture

1

0

0

0

Conservation of natural peatland

Degraded/altered peatland due to cultivation

0

0

1

0

Conservation of natural peatland

Drained peatland

1

0

2

0

Restoration by management of water regime

Drained peatland

1

0

1

0

Decrease GHG emissions

N2O emissions

Conservation of natural peatland

Degraded/altered peatland due to conversion to pasture

0

0

1

0

Conservation of natural peatland

Degraded/altered peatland due to cultivation

0

0

1

0

Conservation of natural peatland

Drained peatland

1

0

1

0

3.      FACTORS INFLUENCING THE EFFECTS ON CLIMATE AND ENVIRONMENTAL IMPACTS

The factors significantly influencing the size and/or direction of the effects on the impacts, according to the synthesis papers included in this review, are reported below. Details about the factors can be found in the summaries of the meta-analyses available in this WIKI.

Table 2: List of factors reported to significantly affect the size and/or direction of the effects on environmental and climate impacts, according to the synthesis papers reviewed. The reference number of the synthesis papers where those factors are explored is given in parentheses.

Impact

Factors

GHG emissions

Fen vs. Bog (Ref5)

4.     SYSTEMATIC REVIEW SEARCH STRATEGY

Table 3: Systematic review search strategy - methodology and search parameters.

Parameter

Details

Keywords

WOS: TS=("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*” OR "bog*") AND TS= ("rewett*" OR "land use change*" OR "land-use change*" OR "conserve*" OR "preserv*" OR "restor*" OR "conver*" OR "drain*" OR "undrain*" OR "protect*" OR "water retention" OR "colonization W/4 Thyfa" OR "colonization W/4 Sphagnum" OR "colonisation W/4 Thyfa" OR "colonisation W/4 Sphagnum" OR "set aside" OR “dry-rewet*” OR “irrigat*” OR “reveget*”) AND TS=("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*"  OR "research synthes*")

AND

TS=("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*”) AND TS= ("plough*" OR "till*" OR "drain*" OR "water use" OR "machinery" OR "integrated pest management*" OR "IPM" OR "fertilis*" OR "fertiliz*" OR "paludicult*" OR "extensive W/4 management*" OR “burn*” OR “sustainable W/4 management*” OR “traditional W/4 management*” OR “prevention W/4 inva*” OR “eradication W/4 inva*” OR “control w/4 inva*” OR “graz*” OR “afforest*”) AND TS=("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*"  OR "research synthes*")

 and

SCOPUS: (SUBJAREA(AGRI OR ENVI) AND TITLE-ABS-KEY("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*” OR "bog*") AND TITLE-ABS-KEY("rewett*" OR "land use change*" OR "land-use change*" OR "conserve*" OR "preserv*" OR "restor*" OR "conver*" OR "drain*" OR "undrain*" OR "protect*" OR "water retention" OR "colonization W/4 Thyfa" OR "colonization W/4 Sphagnum" OR "colonisation W/4 Thyfa" OR "colonisation W/4 Sphagnum" OR "set aside" OR “dry-rewet*” OR “irrigat*” OR “reveget*”) AND TITLE-ABS-KEY("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*"))

AND

(SUBJAREA(AGRI OR ENVI) AND TITLE-ABS-KEY("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*”) AND TITLE-ABS-KEY("plough*" OR "till*" OR "drain*" OR "water use" OR "machinery" OR "integrated pest management*" OR "IPM" OR "fertilis*" OR "fertiliz*" OR "paludicult*" OR "extensive W/4 management*" OR “burn*” OR “sustainable W/4 management*” OR “traditional W/4 management*” OR “prevention W/4 inva*” OR “eradication W/4 inva*” OR “control w/4 inva*” OR “graz*” OR “afforest*”) AND TITLE-ABS-KEY("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*"))

Time reference

No time restriction.

Databases

Web of Science and Scopus: run on 18 May 2022

Exclusion criteria

The main criteria that led to the exclusion of a synthesis paper are: 
 1) The paper did not deal with peatlands or carbon-rich soils or the effects on peatlands could not be disentangled from those on wetlands;, 2) The paper did not compare natural peatlands with nearby degraded or restored peatlands (for peatland conservation);, 3) The paper did not compare restored peatlands with nearby or previously (i.e., comparing impacts before and after restoration) degraded peatlands;, 4) The paper was either a non-systematic review, a non-quantitative systematic review, or a meta-regression without mean effect sizes; and 5) The paper was not written in English. 

The search returned 470 synthesis papers from WOS and SCOPUS on Peatland conservation and restoration plus other 1 retrieved in the search of other farming practices, potentially relevant for the practice object of our fiche. 
From the 471 potentially relevant synthesis papers, 332 were excluded after reading the title and abstract, and 133 after reading the full text according to the above-mentioned criteria. Finally, 6 synthesis papers were selected.

5.     SYNTHESIS PAPERS INCLUDED IN THE REVIEW

Table 4: List of synthesis papers included in this review. More details can be found in the summaries of the meta-analyses.

Ref Num

Author(s)

Year

Title

Journal

DOI

Ref1

Huang, Y; Ciais, P; Luo, Y; Zhu, D; Wang, Y; Qiu, C; Goll, DS; Guenet, B; Makowski, D; De Graaf, I; Leifeld, J

2021

Tradeoff of CO2 and CH4 emissions from global peatlands under water-table drawdown

NATURE CLIMATE CHANGE, 11, 618-622.

10.1038/s41558-021-01059-w

Ref2

Tan, LS; Ge, ZM; Zhou, XH; Li, SH; Li, XZ; Tang, JW

2020

Conversion of coastal wetlands, riparian wetlands, and peatlands increases greenhouse gas emissions: A global meta-analysis

GLOBAL CHANGE BIOLOGY, 26(3), 1638-1653.

10.1111/gcb.14933

Ref3

Xu, SQ; Liu, X; Li, XJ; Tian, CJ

2019

Soil organic carbon changes following wetland restoration: A global meta-analysis

GEODERMA, 353, 89-96.

10.1016/j.geoderma.2019.06.027

Ref4

Xu, SQ; Liu, X; Li, XJ; Tian, CJ

2019

Soil organic carbon changes following wetland cultivation: A global meta-analysis

GEODERMA, 347, 49-58.

10.1016/j.geoderma.2019.03.036

Ref5

Abdalla, M; Hastings, A; Truu, J; Espenberg, M; Mander, U; Smith, P

2016

Emissions of methane from northern peatlands: a review of management impacts and implications for future management options

ECOLOGY AND EVOLUTION, 6(19), 7080-7102.

10.1002/ece3.2469

Ref6

Haddaway, NR; Burden, A; Evans, CD; Healey, JR; Jones, DL; Dalrymple, SE; Pullin, AS

2014

Evaluating effects of land management on greenhouse gas fluxes and carbon balances in boreo-temperate lowland peatland systems

ENVIRONMENTAL EVIDENCE, 3(1), 1-30.

10.1186/2047-2382-3-5

 

Disclaimer: These fiches present a large amount of scientific knowledge synthesised to assess farming practices impacts on the environment, climate and productivity. The European Commission maintains this WIKI to enhance public access to information about its initiatives. Our goal is to keep this information timely and accurate. If errors are brought to our attention, we will try to correct them. However, the Commission accepts no responsibility or liability whatsoever with regard to the information on these fiches and WIKI.


[1] Synthesis research papers include either meta-analysis or systematic reviews with quantitative results. Details can be found in the methodology section of the WIKI.

[2] Joosten, H & Clarke, D. 2002: Wise use of mires and peatlands: Background and principles including a framework for decision making. IMCG/IPS.

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