The ecological and biodiversity conservation values of farm dams: A systematic review

Our results show that farm dams can have a positive influence on biodiversity in landscapes where loss and degradation of natural waterbodies has occurred. However, there are limits to the biodiversity value of farm dams [73,74], and their establishment must consider their con- tribution to biodiversity holistically, taking into account the wider landscape, including the potential impact on or loss of very small wetlands, hydrological regimes, migration patterns [26], and the spread of pests and disease [72]. It is imperative to recognize that while farm dams can potentially provide habitat for biodiversity, their creation and primary purpose is typically for agricultural use rather than biodiversity enhancement and the preservation of nat- ural wetlands should take precedence over the construction of farm dams. The biodiversity values associated with farm dams often emerge as by-products of their construction and man- agement practices. Nevertheless, a farm dam that is well managed in conjunction with effec- tively conserved natural waterbodies can be an important contribution to the biodiversity of a landscape [61]. 4.2. Key knowledge gaps While research on the biodiversity value of farm dams has increased, significant knowledge gaps persist. Despite extensive study on the impact of agricultural intensification on farmland biodiversity, little attention has been given to its potential effects on dams in agricultural land- scapes. We anticipate that intensified land use in farm dam catchments may lead to reduced

species richness and habitat quality [75]. Furthermore, the significance of farm dams in sup- porting biodiversity may be more pronounced in areas with limited alternative habitats and prevalent land use intensification [76–78]. However, detailed comparisons between farm dams and natural wetlands are scarce, comprising less than 10% of the literature. Additionally, research on managing dams alongside natural wetland conservation is limited. We recom- mend that future research on farm dams focuses on: (1) quantifying how the physical charac- teristics of farm dams (e.g., size) influence variables such as species richness, (2) understanding how land use intensity in farm dam catchments influences variables such as water quality, and (3) experimentally quantifying the impact of management practices on the biodiversity values of farm dams. As farm dams are ubiquitous in many agricultural land- scapes, better understanding of their biodiversity values and how these can be enhanced by management could lead to improved conservation outcomes across large areas. Supporting information S1 Checklist. PRISMA 2009 checklist. (DOC) S1 Appendix. Appendix 1. Categories and the corresponding variables and definitions from each study. (TIFF) S2 Appendix. Appendix 2. Complete list of the 102 articles included in this review. Including article name, year of publication, authors and journal of publication. (TIFF) S3 Appendix. Appendix 3. Representative summary table for the risk of bias assessment.

Green cells with (plus) indicate a low risk of bias; yellow cells with (question mark) indicate an unknown risk of bias; red cells with (hyphen) indicate a high risk of bias. (DOCX) PLOS ONE The ecological and biodiversity conservation values of farm dams PLOS ONE | https://doi.org/10.1371/journal.pone.0303504 May 13, 2024 13 / 18