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

While the physical characteristics of farm dams are important predictors of biodiversity, it is also essential to consider the ecological needs and preferences of different taxa. Much of the research focused on macroinvertebrates, macrophytes, and amphibians [58,59] with some popu- lations now heavily reliant on farm dams for their persistence [13,60], while studies focusing on mammals were completely absent. This focus could be because farm dams may not be important habitats for many mammal species, and natural habitats, such as wetlands, may be more suitable [51]. Additionally, many of the focal taxa (e.g., amphibians and reptiles), have very specific habi- tat requirements, are small and have limited dispersal capacity. Therefore, a more holistic approach that considers both the physical characteristics of farm dams and the ecological needs of different taxa is necessary for effective management and conservation of farm dams. 4.1. What is the role of farm dams in conservation? Our systematic review highlighted a prevalent focus on conservation within the research examined. Newer trends in farm dam research suggest a notable transition towards a conserva- tion-centric approach. Studies are increasingly focusing on the role of farm dams in habitat connectivity between naturally occurring waterbodies, the migration of animals across farm- land, and reducing the risk of local extinction [12,15,16]. Many articles identified strong rela- tionships between variables such as surface area, vegetation cover and water quality and the

occurrence of one or more taxonomic groups, suggesting management strategies can be imple- mented to improve habitat value and thus biodiversity, especially when management is done in conjunction with effective conservation of existing wetlands [61]. Several studies [62,63] found that some species (e.g., waterbirds in Spain [27] may choose dams as a permanent source of water and habitat, over waterbodies with fluctuating hydroperiods, such as wetlands, especially during long hot and/or dry periods [63–65]. However, the increase in exotic and predatory species in dams with permanent water poses a challenge to biodiversity [65]. Further research on effective management strategies is essential, laying the foundation for a compre- hensive exploration of farm dam management in support of biodiversity conservation. The biodiversity values of farm dams are dependent on how dams are managed. However, most farm dams are constructed and maintained for economic purposes rather than for con- servation or aesthetics [13]. Older dams that are constructed to be deep and steep-sided go through succession, changing these attributes over time creating shallows with littoral zones that can act as habitat for numerous organisms. However periodic dredging, a common man- agement practice in older dams, returns the dams to their original state [57], greatly reducing the habitat value of these waterbodies [66]. Recent work by Westgate et al. [65] has shown that management practices such as fencing farms dams to limit direct livestock access increases

aquatic and riparian vegetation cover, which is likely to have flow-on benefits for biodiversity conservation. Simple steps such as increasing habitat complexity and heterogeneity within dams, and limiting disturbance, have all been identified as important for farm dam ecosystems [67]. Buffers between dams and farmed areas, such as vegetation strips [68], hedges [69], and riparian strips [70] can help mitigate agricultural impacts on dams, by filtering pollutants, pro- viding corridors between habitats, and reducing stock access. Additionally, buffers can be designed to direct ecosystem services from farm dams to agricultural lands, such as filtering water runoff to improve soil fertility and providing habitat for pollinators to enhance crop pro- ductivity. There has also been success in countries such as Australia [71] and New Zealand [72], with programs that reward landholders for making biodiversity friendly farming deci- sions such as the ones described above. These programs could be tailored specifically for farm dams. Such programs may lead to partnerships among multiple stakeholders in agroecosys- tems–farmers, government, practitioners, scientists, NGOs, and the wider population [72]. PLOS ONE The ecological and biodiversity conservation values of farm dams PLOS ONE | https://doi.org/10.1371/journal.pone.0303504 May 13, 2024 12 / 18