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Table 1 List of variables to code from the studies, including key sources of heterogeneity known to influence the effects of herbivores on tundra ecosystems

From: What are the effects of herbivore diversity on tundra ecosystems? A systematic review protocol

Topic Coding variable Variable description Source
Article ID author_list List of authors P
  title Title of the publication P
  year Year of publication P
  journal Journal or publishing house P
  language Language of the publication P
  study_ID Unique ID number for study C
  searchable_pdf Whether the document allows for automated text searches P
Study location country Country or region name P
  locality Site name describing the locality, as specified in the study P
  coordinate_source Whether coordinates are provided in the text, based on maps, figures or place names P
  coordinates_N, coordinates_E Geographic coordinates in decimal degrees P
  elevation Elevation (m a.s.l.) P
  elevation_DEM Elevation (m a.s.l.) extracted from digital elevation model D
Study type study_design Whether the study involves experimental manipulations, observational approaches or whether the study design is unclear C
  diversity_contrast Approach used to create or assess the difference in herbivore diversity, such as exclosures or spatial contrasts C
  size_selective_exclosures Does the study use different exclosures that prevent access of different sized herbivores? C
  spatial_extent Size of the study area C
  spatial_resolution Spatial scale at which the outcome is reported for each study C
  temporal_resolution Interval between measurements of the outcome C
  sampling_frequency Frequency of measurements C
  year_start Year when the study started P
  year_end Year when the study finished P
Exposure and comparator herbivore_data How is the composition of the herbivore assemblages assessed? C
  herbivore_ID_higher_diversity Species (or group) list in the areas with higher herbivore diversity P
  herbivore_ID_lower_diversity Species (or group) list in the areas with lower herbivore diversity P
Outcome measured_response_variable What was measured in areas exposed to different herbivore diversity? P/C
  reported_units Units in which the response variable is reported; "unitless" if there is no unit P
  value_higher_diversity Value of the outcome in the higher diversity area P
  value_lower_diversity Value of the outcome in the lower diversity area P
  value_type Does the value refer to the mean, median, etc P
  variability_higher_diversity Variability of the outcome in the higher diversity area P
  variability_lower_diversity Variability of the outcome in the lower diversity area P
  variability_type Type of variability measurement (SE, confidence intervals (CI), etc.) P
  sample_size_higher_diversity Number of observations in the higher diversity area P
  sample_size_lower diversity Number of observations in the lower diversity area P
  effect_size Value of the comparison between areas with different diversity P
  effect_size_variability Variability of the comparison P
  effect_size_variability_type Type of variability measurement (SE, confidence intervals (CI), etc.) P
  effect_size_direction Direction of the comparison, or unclear C
  effect_size_sample_size Number of observations for the comparison if reported P
  effect_size_type Type of comparison (e.g. model estimate) C
  effect_size_comments Any additional comments C
  statistical_test Type of statistical test reported (e.g. paired t-test) P
  statistical_test_value Value of the test statistic P
  statistical_test_df Degrees of freedom of the statistic P
  statistical_test_p p-value of the statistical test P
  outcome_comments Any additional comments C
  more_data Is there data available in the paper that is not extractable in its current form? C
Study validity assessment bias_risk_criterion1 Biases due to uncontrolled confounding variables that influence both the herbivore diversity levels and the response variable C
  bias_risk_criterion2 Biases arising from systematic differences in the selection of areas into the study or analyses after treatment C
  bias_risk_criterion3or4 Biases arising from misclassification or measurement of contrasts of herbivore diversity (observational studies) or treatments (experimental studies) C
  bias_risk_criterion5 Biases arising from systematic differences in measurements of outcomes C
  bias_risk_criterion6 Biases in reporting of study findings C
  bias_risk_criterion7 Biases due to error in applied statistical methods C
  bias_risk_comments Please indicate any relevant comments; if there were confounding variables please report them here C
Context distance_to_treeline Distance (km) to southern border of arctic subzone E D
  distance_from_coast Distance (km) to the coast D
  bioclimatic_zone Bioclimatic zone A to E, or "other" D
  temperature Temperature related variable(s) extracted from WorldClim D
  precipitation Precipitation related variable(s) extracted from Worldclim D
  growing_season Duration of growing season (days) D
  productivity Value of NDVI (vegetation greenness) D
  recent_warming Extent of recent warming D
  recent_greening Extent of recent greening D
  extent_of_recent__change Extent of recent change in growing season length D
  soil_chemistry Soil chemistry C
  soil_texture Broad categories of soil texture C
  soil_moisture Soil moisture as described in the study C
  soil_type Soil type as reported by the authors P
  soil_type_D Soil type D
  permafrost Presence of permafrost C
  permafrost_D Presence of permafrost D
  habitat_type Habitat types using the broad categories defined in CAVM C
  habitat_type_D Habitat types D
  management_focus Whether the study is framed within a management context C
  conservation_focus Whether the study is framed within a conservation context C
  1. The coding variables are grouped into broader topics. Source indicates where the data is extracted from: P for publication, D for digital spatial data layers and C classified by the reviewers based on information available in the publication. More detailed descriptions, examples of the variables and references for the digital spatial data (D) are provided in Additional file 3