Three new SMs have recently been completed on the subjects of agricultural impacts on soil organic carbon (SOC) (Haddaway et al. 2015b), management of protected forests (Bernes et al. 2015) and on-farm mitigation measures for improving water quality (Randall et al. 2015). These maps have used state-of-the-art methodology in systematic mapping, including in-depth stakeholder engagement from the outset of the review projects, comprehensive assessment of all relevant review bibliographies, the use of GIS to visually display the contents of the map databases. These projects demonstrate the utility of SMs.
Impacts of agricultural management on soil organic carbon (SOC)
Swedish stakeholders, including the Swedish Board of Agriculture and the Swedish Environmental Protection Agency, identified the need to better understand the relationship between management practices on arable farmland and stocks of SOC. A SR was initiated, focusing on research from the warm temperate and snow climate zones (according to the Köppen–Geiger climate classification; Kottek et al. 2006), and based on a predetermined methodology set out in a detailed protocol published in EEJ (Söderström et al. 2014). When the search strategy was implemented, however, the volume of evidence returned was extensive, and a decision was made for practical reasons of resource availability to produce a SM first. This map described studies across a range of agricultural management practices (soil amendments, crop rotation, fertiliser application and tillage), with interventions identified iteratively where study length was 10 years or more (to ensure SOC changes were given time to manifest themselves).
A total of 740 articles were included in the SM (24547 search results > 5735 relevant titles > 1814 relevant abstracts > 740 relevant full texts). One of the outputs of this SM was a map report, which described the background, methods and results of the mapping exercise, and discussed the range and nature of the evidence base. In addition, a SM database was published, providing details relating to the citation of the article describing the study, the study setting, the experiment studied, the methodology used to measure the experiment soil conditions, and the location, units and format of the quantitative findings of the study. Furthermore, a web-based GIS was produced based on the contents of the map. This GIS allows users to filter subsets of studies on a spatial map (as opposed to a metaphorical evidence map), forming a different and user-friendly interface to the database.
The SM authors highlighted several knowledge gaps (e.g. a paucity of studies from Russia) and knowledge gluts (e.g. a multitude of studies investigating conservation tillage), and noted a lack of spatial and temporal replication and frequently missing information (such as study methods, location and description of the interventions) within included articles. This information was detailed within the SM report and may prove useful for primary researchers (knowledge gaps, methodological deficiencies), secondary researchers (knowledge gluts), research funders (knowledge gluts, knowledge gaps, research deficiencies) and decision-makers (knowledge gaps, knowledge gluts) alike. Following on from the SM, the research team behind the review is currently undertaking two full SRs on subsets of the evidence identified in the map. One review will synthesise the findings of studies investigating the relative impacts of different tillage intensities on soil organic carbon. The second review will include all interventions, but will focus purely on studies with long-time series data (i.e. 30 years or more, with multiple measurements through time). These two full reviews will involve an update to the original searches to ensure that recently published evidence is included. Both reviews will also include a full quantitative synthesis (i.e. meta-analysis). Further knowledge gluts were identified in the SM that may also be synthesised by the review team if resources allow.
Impacts of active management on biodiversity in forests set aside for conservation or restoration
Conservationists in Sweden and several other countries are currently involved in a discussion of the best means of preserving or restoring forest biodiversity in reserves and other areas that have been set aside from commercial forestry. One management option is non-intervention; other options include various forms of active management such as prescribed burning, thinning, partial harvesting, grazing or exclusion from grazing. Current practices and recommendations for the management of forest set-asides are often based on traditions (i.e. the “free-development” paradigm) rather than scientific evidence, however. Swedish stakeholders (including County administrators, landowners and environmental NGOs) therefore suggested a SR of all available evidence on the biodiversity effects of relevant forms of management in cool temperate and boreal forests.
Since the evidence base was likely to be quite heterogeneous, including studies of a variety of interventions and many different aspects of biodiversity, it was recognised from the outset that systematic mapping might be useful as a first step towards full SR of specific management options. The review team searched not only for studies of interventions in actual forest set-asides, but also for appropriate evidence from commercially managed forests, since some practices applied there may equally be useful for conservation or restoration purposes.
Around 800 relevant studies were found (16 484 search results > 6142 relevant titles > 1762 relevant abstracts > 798 relevant full texts), almost two-thirds of which had been conducted in North America. Most of the rest had been performed in Central or Northern Europe. These studies were presented much in the same way as those in the SOC SM described above, i.e. in a SM report, an associated database with details of each study, and a separate GIS which made it possible to plot and identify all included studies (or any selection of them) on a cartographic map. The details provided about the studies included descriptive data (meta-data) on locations, study design, forest stands, interventions, types of biodiversity outcomes and focal species.
Knowledge gaps identified within the SM included a lack of studies on hydrological interventions (such as restoration of forested wetlands) and traditional silvicultural systems that are presently uncommon (such as coppicing and pollarding). As in the SOC SM, there was also a paucity of useful Russian studies.
Based on the availability of relevant studies, the existence or absence of earlier reviews, and needs expressed by stakeholders, the authors of the SM finally identified four subtopics for which it would be feasible to complete full SRs: (1) What are the impacts of thinning, partial harvesting and understorey removal on the diversity of ground vegetation in mature temperate and boreal forest? (2) What are the impacts of temperate and boreal forest stand- and tree-scale interventions on dead wood and saproxylic species? (3) What is the effect of prescribed burning in temperate and boreal forest on biodiversity, beyond tree regeneration, pyrophilous and saproxylic species? and (4) What are the impacts of manipulating the pressure of grazing and browsing by livestock or wild ungulates on the diversity of temperate and boreal forest plants and invertebrates?
Effectiveness of on-farm mitigation measures for improving water quality
Agriculture contributes high amounts of nitrogen, phosphorous, sediments, pesticides, and with livestock also potential human pathogens to waterways that all contribute to a decline in water quality (Edwards and Withers 2008; Kay et al. 2008; Collins et al. 2009; Defra 2009). This decline can directly impact the environment and its associated ecosystem services, whilst also taxing limited government funding available for environmental management. EU member states are obliged under the Water Framework Directive (WFD) to mitigate water pollution, but as yet no systematic approach has been made to identify and assess the various mitigation measures used.
In their SM, Randall et al. (2015) collate research from temperate countries pertaining to six key mitigation measures: (1) slurry storage, (2) catch crops, (3) woodland creation, (4) controlled trafficking, (5) subsoiling and (6) vegetated buffer strips.
The reviewers included 718 studies in the map (74 086 search records > 1359 relevant titles > 718 relevant abstracts > 495 relevant full texts). Buffer strips were the most frequently studied of the six interventions, with cover crops and slurry storage also commonly investigated. Very few/no studies had focused on woodland creation, controlled trafficking and subsoiling. In terms of measured outcomes, nitrogen was most frequently studied, followed by phosphorus, sediment, pesticides and bacterial pathogens.
The majority of research in this area was found to focus on mitigating nitrogen pollution and on the use of buffer strips and catch crops. Knowledge gaps were therefore found for the remaining four mitigation interventions and outcomes other than nitrogen. Furthermore, the reviewers found relatively few robust studies: few used long-term datasets, measured across seasons, possessed well-matched controls, measured baseline data, or sampled within fields and watercourses. These research quality gaps identify the benefit that would come from adding more reliable research to the evidence base.