Table 1.
Categories and search terms or key words used in the literature review search process.
Table 2.
Parameters and tags used in the systematic classification of papers or case studies selected (in order of relevance).
Parameters 11 and 12 were used to select a subset of case studies to address the secondary objective.
Fig 1.
PRISMA flowchart.
Fig 2.
Studies by type of intervention.
Percent distribution of study cases according to type of intervention described in the papers (a) and type of intervention based on the reclassification (b). Only study cases reporting on a direct measures of water yield are included (n = 308).
Fig 3.
Water yield responses measured directly.
Percent distribution of results in study cases that directly measured changes in annual water yield/channel runoff (n = 308) (a), and baseflow (n = 53) (b).
Fig 4.
Water yield by type of intervention.
Percent distribution of direct metrics of water yield responses according to intervention type group.
Fig 5.
Water yield responses measured indirectly.
Percent distribution of study cases with a positive, negative, or neutral effect of forest cover restoration or expansion on indirect water yield metrics, including (a) flooding frequency or magnitude of peak flows (n = 43), (b) groundwater level or recharge (n = 15), and (c) infiltration capacity or soil infiltration (n = 18).
Fig 6.
Distribution of studies by forest type.
Percent distribution of native, non-native, and mixed forest types among all studies selected in the review (a) and within each group of forest intervention (b). The results are based on study cases reporting on a direct measures of water yield (n = 308).
Fig 7.
Magnitude of water yield change by forest type.
Box plot showing the median, quartiles, maximum and minimum, and outlier values for changes in water yield following forest restoration or cover expansion. These results are based on a subset of case studies selected for meta-analysis (n = 37). NA refers to the category of studies with no information on tree species or forest types.
Fig 8.
Distribution of studies by spatial and temporal scale categories.
Percent distribution of study cases according to catchment area (a) and time scale of water yield dataset (b). The case studies included reported on water yield results from direct measurements.
Fig 9.
Meta-analyses of water yield response versus temporal and spatial scale of studies.
Scatter plots with percentage change (decline) in water yield versus period of data collection (a) and catchment size in km2 (b). The data included are from a subset of study cases selected for meta-analyses, and the x-axis are log10 scaled. Spearman correlation results are indicated for both datasets.
Fig 10.
Studies with field and model water yield data.
Percent distribution of study cases with data collected with different methods (a), and relative abundance of studies with field or model data according to spatial (b) and temporal (c) scales.
Fig 11.
Geographic location of study cases and their water yield outcomes.
Global distribution of study cases providing data on changes in water yield following forest restoration or forest cover expansion. The pie charts indicate the distribution of water yield responses reported in the studies from the different regions. Red represents a negative response, green a positive response, and purple mixed results. Neutral response is represented by light blue. Source for the world map is the US National Park Service (Natural Earth physical map; https://www.arcgis.com/home/item.html?id=c4ec722a1cd34cf0a23904aadf8923a0).
Table 3.
Number of study cases in each continental region.
The number of cases are presented as absolute numbers and also normalized by the land area of the respective continent.
Fig 12.
Study cases per Köppen-Geiger climate class.
Percent distribution of study cases according to climate classes using the Köppen-Geiger classification system. The main climate groups include: (A) tropical, (B) dry arid and semiarid, (C) mild temperate, (D) continental, and (E) polar/alpine. The subgroups are divided according to average annual and monthly temperatures, total precipitation and precipitation seasonality.