International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 217-228 http://ecoevopublisher.com/index.php/ijmec 22 2 building DAMS is rather complex and varies depending on the ecological habits of different fish species. Small still water tolerant fish (such as crucian carp, American killifish, etc.) often thrive in beaver ponds, while large migratory fish that need to swim long distances upstream to spawn (such as Atlantic salmon) may be blocked by dam bodies (Auster et al., 2021; Tape et al., 2022). However, many case studies have shown that beaver ponds provide sheltered habitats for fish to avoid drought and cold, abundant food and spawning grounds, and have positive effects on the overall fish community (Brazier et al., 2021). In a long-term study in Scotland, positive changes occurred in the population structure of brown trout (Salmo trutta) in streams after the introduction of beavers (Needham et al., 2021). 4.2 Changes in terrestrial plant communities and bird diversity The ecological engineering of beavers is not limited to aquatic systems; it also has a wide-ranging impact on the terrestrial ecology of riverbanks, typically manifested as changes in vegetation structure and an increase in bird diversity. Beaver dam construction triggers secondary succession and community replacement of riverbank vegetation. Beavers have created a new pattern of interlaced forest and water and inlaid vegetation through flooding and foraging. The terrestrial plant community shows higher spatial heterogeneity (Orazi et al., 2022). Bird diversity is another typical example driven by the beaver project. Beaver wetlands offer open water surfaces and foraging shallows for waterfowl and wading birds, while standing dead trees attract woodpeckers and cave nest birds to make use of them. In studies in central Europe, beaver activity significantly increased the richness and number of birds along rivers: the number of breeding bird species and individual density recorded in beaver sections were higher than those in the unmodified control sections (Fedyne et al., 2024). The Beaver Project has formed a series of positive ecological chain reactions from plants to invertebrates to birds by enriching habitat types and food resources (Orazi et al., 2022). 4.3 Establishment of microhabitats and rare species shelters Beaver activities form numerous special microhabitats in river landscapes, providing crucial shelters and habitats for some rare or endangered species. For instance, beaver wetlands often play the role of "refugia" in drought or fire conditions. Beavers increase humidity by storing water and create miniature shelters for species survival in increasingly frequent extreme droughts and fire events (Auster et al., 2021). For instance, in the winter of cold high-latitude regions, the subglacial waters covered by beaver ponds provide an unfrozen deep-water habitat for fish and amphibians, where many species can escape the deadly low temperatures and hypoxic conditions (Tape et al., 2022). In addition, beaver habitats often feature a rich variety of microhabitats, such as slow-flowing mudflats, shallow water depressions, and dead wood accumulation zones, which may be essential habitats for certain rare species. Beavers construct diverse microhabitat networks through their engineering behaviors, which not only shelter common species but also provide irreplaceable habitats for some rare species sensitive to environmental conditions (Orazi et al., 2022). 5 Regional Ecosystem Services and Beaver Coexistence Management 5.1 Enhancement of ecosystem services: water storage, flood control and carbon sink functions Beaver activities bring a variety of service functions to the ecosystem, including water resource regulation and storage, flood control and disaster reduction, water quality purification and carbon sink enhancement, etc. Firstly, the small reservoirs and wetlands formed by beavers building DAMS play a significant role in the "natural water storage" of river basins. They increase groundwater recharge and soil moisture content, and improve the availability of water resources during the dry season. This is of positive significance for alleviating water shortage during the dry season and enhancing the guarantee of agricultural irrigation. The Beaver Dam has achieved certain flood control functions by reducing flood peaks and delaying runoff. This ecological service has attracted much attention in areas with increasing flood risks. Beavers have been introduced as one of the measures for natural flood management in places such as the UK (Puttock et al., 2021). Beaver Wetland offers water purification services. Slow flow and wetland vegetation make beaver ponds "biological filters" that can remove agricultural non-point source pollutants such as nitrogen and phosphorus (Grudzinski et al., 2022). In addition, beaver activities also have a significant impact on the carbon cycle. The wetlands it creates deposit a large amount of organic peat, sequestering carbon elements and having carbon sink functions (Thompson et al., 2021).
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