Bioscience Evidence 2024, Vol.14, No.4, 172-183 http://bioscipublisher.com/index.php/be 177 in the presence of species such as moose, otters, and pine martens (Nummi et al., 2019). Similarly, beaver ponds have been found to host a greater number of bird species and higher abundances of bats and birds compared to river and forest habitats (Orazi et al., 2022). The increased structural heterogeneity and productivity of vegetation in beaver-influenced areas also contribute to higher diversity and abundance of invertebrates, such as moths and flying insects (Andersen et al., 2023). These findings underscore the role of beavers in enhancing biodiversity through their ecosystem engineering activities. 6.3 Case studies of biodiversity improvements in beaver-influenced areas Several case studies highlight the positive impact of beavers on biodiversity. In Klosterheden, Denmark, the reintroduction of beavers led to increased biomass of flying invertebrates and diversity of moths, along with enhanced vegetation productivity and structural heterogeneity (Andersen et al., 2023). In a boreal setting, beaver patches were found to significantly increase mammalian species richness and occurrence, with specific species such as moose and otters showing a preference for beaver-engineered habitats (Nummi et al., 2019). In Germany's oldest national park, beaver ponds supported a higher number of species of conservation concern and greater abundances of birds and bats compared to river and forest plots, demonstrating the beaver's role in promoting biodiversity in mountain forest ecosystems (Orazi et al., 2022). Additionally, in southern Finland, beaver-created wetlands were found to support higher species richness and abundance of water beetles, particularly in newly formed beaver ponds (Nummi et al., 2021). These case studies collectively illustrate the transformative role of beavers in enhancing biodiversity across different ecosystems and geographic regions. 7 Soil and Nutrient Cycling 7.1 Influence on soil composition and erosion control Beavers, as ecosystem engineers, significantly influence soil composition and erosion control through their dam-building activities. The construction of beaver dams impounds water, which leads to the creation of wetlands. These wetlands enhance sediment deposition, thereby reducing soil erosion and increasing soil stability (Figure 3) (Brazier et al., 2020; Larsen et al., 2021). The increased water retention in beaver-modified landscapes also promotes the development of anaerobic soil conditions, which can alter soil composition by increasing organic matter content and nutrient availability (Larsen et al., 2021). Additionally, the presence of beaver ponds can lead to the formation of new soil layers as sediments settle, further contributing to soil stability and reducing erosion (Brazier et al., 2020). 7.2 Role in nutrient deposition and cycling Beavers play a crucial role in nutrient deposition and cycling within ecosystems. Their activities increase the residence time of water and nutrients, which enhances nutrient cycling processes (Larsen et al., 2021). Beaver dams trap organic matter and sediments, leading to increased deposition of nutrients such as nitrogen and phosphorus in the soil (Cheng et al., 2019; Larsen et al., 2021). This nutrient enrichment supports microbial activity and plant growth, thereby enhancing the overall productivity of the ecosystem. Furthermore, the creation of wetlands by beavers promotes the development of diverse microbial communities that are essential for nutrient cycling, including nitrogen fixation and decomposition processes (Camenzind et al., 2018; Mercado-Blanco et al., 2018). The increased nutrient availability in beaver-modified landscapes can also lead to higher primary production and greater biodiversity (Nummi et al., 2019; Larsen et al., 2021). 7.3 Benefits to agricultural lands and forest ecosystems The presence of beavers and their ecosystem engineering activities provide several benefits to agricultural lands and forest ecosystems. In agricultural landscapes, beaver-created wetlands can improve water quality by trapping sediments and nutrients, reducing the need for artificial fertilizers and mitigating the impacts of agricultural runoff (Brazier et al., 2020; Larsen et al., 2021). These wetlands also provide habitat for a variety of wildlife, which can enhance biodiversity and ecosystem resilience (Nummi et al., 2019). In forest ecosystems, beaver activities contribute to soil fertility by increasing nutrient cycling and deposition, which supports tree growth and forest health (Cheng et al., 2019; Legout et al., 2020). The enhanced soil stability and reduced erosion in beaver-modified landscapes also protect forest ecosystems from degradation and promote long-term sustainability
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