Grassland conservation and restoration_GENERAL

Data extracted in December 2021

Note to the reader: This general fiche summarises the environmental and climate impacts of GRASSLAND CONSERVATION AND RESTORATION found in a systematic review of 10 synthesis research papers [1]. These papers were selected from an initial number of 1022 obtained through a systematic literature search strategy, according to the inclusion criteria reported in section 4.

As each synthesis research paper involves a number of primary research papers - ranging from 13 to 259, the assessment of impacts relies on a large number of results obtained mainly in field experiments (carried out in situations close to real farming environment), and sometimes in lab experiments or from model simulations.

1. DESCRIPTION OF THE FARMING PRACTICE

Description

Grasslands are areas of land predominantly covered by communities of grass-like plants and forbs and may include sparsely occurring trees and shrubs. In the Eurostat classification, percentages of area covered by such canopies are limited to less than 10 % in the case of trees and to less than 20 % in the case of shrubs (i.e., low woody plants capable of reaching heights of up to 5 metres [2]) or shrubs and trees together [3]. However, in the scientific literature reviewed here, grasslands are usually more broadly defined and might not fully meet such canopy limits.
This review includes a wide variety of grassland types: savannah, grassy deserts, seasonally flooded grasslands, prairies, meadows, pastures, rangelands, salt-marshes, bioenergy perennial grasslands, calcareous grasslands and wooded grasslands. Grasslands differ in terms of:

management intensity: natural, semi-natural, improved and intensively managed,
management history: permanent and temporary,
successional stage: old successional and secondary grasslands,
biomes and climates: semi-arid, temperate, tropical, Mediterranean, tundra, alpine, subalpine, artic and subartic.

Fodder crops are not included as grasslands.
Grassland conservation refers to the preservation (i.e., no transformation to other land uses) of old successional natural grasslands. Old successional natural grasslands are grasses and forbs communities with no major human-induced structural or functional alterations so that their current management closely resembles historical, endogenous disturbance regimes (e.g., grazing intensity and fire frequency) [4]. In the scientific literature, these ecosystems are also referred as old-growth, ancient, remnant or native grasslands.
Grassland restoration includes active and passive restoration methods usually aiming at enhancing plant community diversity, what is then expected to have cascading positive effects in higher trophic levels5. This review includes several restoration methods: sowing of seed mixtures, addition of soil and hay, reintroduction of grazing and burning as active restoration methods, and abandonment of agricultural use as passive restoration method. In this review, we only consider the restoration of former grassland areas degraded by agricultural use (i.e., degradation due to mining or other land uses are excluded). We define secondary grasslands as the herbaceous communities that assemble after destruction (here, by agricultural use) of old successional natural grasslands [4] where the restoration efforts are conducted.

Key descriptors

For the exploration of grassland conservation, this review includes the spatial comparison between preserved old successional natural grasslands (intervention) and nearby secondary grasslands, either restored or degraded, as control.
For the exploration of grassland restoration, this review includes spatial and temporal comparisons between restored grasslands (intervention) and croplands or secondary grasslands after crop abandonment as controls. Spatial comparisons are those conducted simultaneously between restored grasslands and nearby croplands (or secondary grasslands after crop abandonment). Temporal comparisons are those conducted in the same site before (when land use was cropland or abandoned cropland) and after restoration into grassland.
In this review, grassland restoration includes restoration into different types of grasslands, including perennial bioenergy grasslands.
This review does not include grazing or other management practices (i.e, soil amendment and fertilisation, mowing, increasing grass species richness) conducted in grasslands, which are assessed in separate sets of fiches.

2. DESCRIPTION OF THE IMPACTS OF THE FARMING PRACTICE ON CLIMATE AND THE ENVIRONMENT

We reviewed the impacts of more diverse rotation (with two or more crops) compared to monocropping or simpler rotations.

We reviewed the impacts of the conservation of old successional natural grasslands compared to secondary grassland (Table 1) and the restoration of grasslands in replacement of croplands or of secondary grasslands (Table 2).

The tables below show the number of synthesis papers reporting positive, negative or no effect, based on the statistical comparison of the intervention and the control. In addition, we include the number of systematic reviews reporting relevant results, if any, without statistical test of the effects (“uncertain”). The numbers between parentheses indicate the number of synthesis papers with a quality score of at least 50%. Details on quality criteria can be found in the methodology section of this WIKI.

Out of the 10 synthesis papers selected, 9 reported studies conducted in Europe while one did not report the geographical origin of the studies included. All the synthesis papers have a quality score higher than 50%.

Table 1. Impacts of the conservation of old successional natural grassland compared to secondary grassland.

Impact	Positive	Negative	No effect	Uncertain
Increase biodiversity	2 (2)	0	1 (1)	0
Increase pollination	0	0	1 (1)	0
Increase carbon sequestration	1 (1)	0	0	0

Table 2. Impacts of the restoration of grassland compared to cropland or secondary grassland.

Impact	Comparator (Land use previous to restoration)	Positive	Negative	No effect	Uncertain
Increase biodiversity	Cropland	1 (1)	0	2 (2)	0
Decrease GHG emissions	Cropland	1 (1)	0	0	0
Decrease nutrient leaching and run-off	Cropland	1 (1)	0	0	0
Increase pollination	Secondary grassland	1 (1)	0	0	0
Increase soil nutrients	Cropland	0	1 (1)	0	0
Increase carbon sequestration	Cropland	3 (3)*	0	0	0
Increase carbon sequestration	Secondary grassland	0	1 (1)**	0	0

*In one of these synthesis papers the previous cropland use is restored into perennial bioenergy grassland.

**In this review paper the previous secondary grassland use is restored into perennial bioenergy grassland.

3. DESCRIPTION OF THE KEY FACTORS INFLUENCING THE SIZE OF THE EFFECT

Only the factors explicitly studied in the reviewed synthesis papers with a significant effect are reported below. Details regarding the factors can be found in the Summaries of the meta-analyses.

Impact	Factors
Increase biodiversity	Age of secondary grassland (ref 2), Presence of remnant vegetation (ref 9)
Increase pollination	Pollinator taxa (ref 3), Time since treatment (ref 3), Restoration method (ref 3)
Increase carbon sequestration	Abandonment time (ref 6), Climate (ref 6), Initial soil organic carbon stock (ref 6), Soil sampling depth (ref 11)

4. SYSTEMATIC REVIEW SEARCH STRATEGY

Keywords	TS=("grazing" OR "grassland" OR "pasture" OR "rangeland")) AND TS=(("meta-analy" OR "systematic* review" OR "evidence map" OR "global synthesis" OR "evidence synthesis" OR "research synthesis") or TITLE-ABS-KEY: ("grazing" OR "grassland" OR "pasture" OR "rangeland") AND TITLE-ABS-KEY ("meta-analy" OR "systematic review*" OR "evidence map" OR "global synthesis" OR "evidence synthesis" OR "research synthesis")
Search dates	No time restrictions
Databases	Web of Science and Scopus, run in September 2021
Selection criteria	The main criteria that led to the exclusion of a synthesis paper were when the paper: 1) does not deal with terrestrial grasslands or the effects on grasslands can not be disentangled from other land uses; 2) does not compare old successional natural grasslands with nearby secondary grasslands (for grassland conservation); e.g., comparisons between old successional natural grasslands and croplands were excluded; 3) does not compare restored grasslands with nearby or with previous cropland use, including tree plantations (for grassland restoration); e.g., land use changes from grassland to cropland were excluded; 4) is either a non-systematic review, a non-quantitative systematic review, or a meta-regression without mean effect sizes; 4) is not written in English. Due to the high number of potentially valid synthesis papers, we applied additional exclusion criteria: 5) the paper does not include studies conducted in Europe; 6) the paper only reports impacts on crop or animal production, and no environmental impacts. Synthesis papers that passed the relevance criteria were subject to critical appraisal carried out on a paper-by-paper basis. The search returned 1022 synthesis papers potentially relevant for the practice object of our fiche. From the 1022 potentially relevant synthesis papers, 661 were excluded after reading the title and abstract, and 351 after reading the full text according to the above-mentioned criteria. Finally, 10 synthesis papers were selected for grassland conservation and restoration.

5. LIST OF SYNTHESIS PAPERS INCLUDED IN THE REVIEW

Ref. Num	Authors	Year	Title	Reference	DOI
1	Zhang, YS; Pan, BB; Lam, SK; Bai, E; Hou, PF; Chen, DL	2021	Predicting the ratio of nitrification to immobilization to reflect the potential risk of nitrogen loss worldwide	ENVIRONMENTAL SCIENCE AND TECHNOLOGY, 55(11), 7721-7730.	10.1021/acs.est.0c08514
2	Nerlekar, AN; Veldman, JW	2020	High plant diversity and slow assembly of old-growth grasslands	PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 117(31), 18550-18556.	10.1073/pnas.1922266117
3	Sexton, AN; Emery, SM	2020	Grassland restorations improve pollinator communities: A meta-analysis	JOURNAL OF INSECT CONSERVATION, 24(4), 719-726.	10.1007/s10841-020-00247-x
4	Wu, JJ; Chen, Q; Jia, W; Long, CY; Liu, WZ; Liu, GH; Cheng, XL	2020	Asymmetric response of soil methane uptake rate to land degradation and restoration: Data synthesis	GLOBAL CHANGE BIOLOGY, 26(11), 6581-6593.	10.1111/gcb.15315
5	Kampf, I; Holzel, N; Storrle, M; Broll, G; Kiehl, K	2016	Potential of temperate agricultural soils for carbon sequestration: A meta-analysis of land-use effects	SCIENCE OF THE TOTAL ENVIRONMENT, 566, 428-435.	10.1016/j.scitotenv.2016.05.067
6	Harris, ZM; Spake, R; Taylor, G	2015	Land use change to bioenergy: A meta-analysis of soil carbon and GHG emissions	BIOMASS AND BIOENERGY, 82, 27-39.	10.1016/j.biombioe.2015.05.008
7	MacDonald, GK; Bennett, EM; Taranu, ZE	2012	The influence of time, soil characteristics, and land-use history on soil phosphorus legacies: A global meta-analysis	GLOBAL CHANGE BIOLOGY, 18(6), 553-565.	10.1111/j.1365-2486.2012.02653.x
8	Felton, A; Knight, E; Wood, J; Zammit, C; Lindenmayer, D	2010	A meta-analysis of fauna and flora species richness and abundance in plantations and pasture lands	BIOLOGICAL CONSERVATION, 143(3), 545-554.	10.1016/j.biocon.2009.11.030
9	Attwood, SJ; Maron, M; House, APN; Zammit, C	2008	Do arthropod assemblages display globally consistent responses to intensified agricultural land use and management?	GLOBAL ECOLOGY AND BIOGEOGRAPHY, 17(5), 585-599.	10.1111/j.1466-8238.2008.00399.x
10	Guo, LB; Gifford, RM	2002	Soil carbon stocks and land use change: a meta analysis	GLOBAL CHANGE BIOLOGY, 8(4), 345-360.	10.1046/j.1354-1013.2002.00486.x

[1] Synthesis research papers include either meta-analysis or systematic reviews with quantitative results.

[2] https://ec.europa.eu/eurostat/statistics-explained/index.php?title=Glossary:Shrubland

[3] https://ec.europa.eu/eurostat/statistics-explained/index.php?title=Glossary:Grassland

[4] Nerlekar & Veldman. 2020. High plant diversity and slow assembly of old-growth grasslands. PNAS 117, 18550–18556.

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1. DESCRIPTION OF THE FARMING PRACTICE

2. DESCRIPTION OF THE IMPACTS OF THE FARMING PRACTICE ON CLIMATE AND THE ENVIRONMENT

3. DESCRIPTION OF THE KEY FACTORS INFLUENCING THE SIZE OF THE EFFECT

4. SYSTEMATIC REVIEW SEARCH STRATEGY

5. LIST OF SYNTHESIS PAPERS INCLUDED IN THE REVIEW