Happy International Beaver Day! We're excited to spend the day celebrating our resident beavers at Cincinnati Nature Center, and the work that they do here and elsewhere, not just for their own benefit.

You've probably heard that beavers are “ecosystem engineers”, but what does that mean?  

Simply put, ecosystem engineers modify physical processes in an ecosystem to suit their own needs. This can either be done through the engineer’s own physical structure (autogenic ecosystem engineer) or through their behaviors (allogenic ecosystem engineer). Trees are an example of an autogenic engineer because they provide the physical structure of a forest through their own living and dead body parts. Beavers and other allogenic engineers (hello humans!) alter physical processes through their behaviors.

Beaver’s most well-known act of engineering is the construction of dams. Beavers build dams across streams to slow the flow of water and create deep pools upstream of their dam, inundating the floodplain. These deeper pools of water provide protection for beavers, who are much more vulnerable to predation on land than in water. The obstruction of streamflow caused by beaver dams has broader ecosystem benefits, extending both upstream and downstream of the wetland. Beaver dams slow the velocity of water which dampens the erosive force of water downstream, and trap sediments and nutrients, which decreases the harmful effects of smothering downstream habitat (Fairfax & Westbrook, 2024; Burgher et al., 2025). This can be especially helpful in developed areas where human land use has led to increased runoff, erosion, and stream velocities during rain events.  

Beaver dams provide such good structure, function and ecosystem services that “Beaver Dam Analogs” (BDAs) have become a popular nature-based solution in stream restoration. These human-made structures use the same materials as true beaver dams—such as sticks, grasses, leaf litter, and mud—from the surrounding environment to create “speed bumps” to slow the flow of water and increase floodplain connectivity. Although man-made, BDAs are permeable, semi-temporary structures that allow for natural changes to the stream, unlike conventional man-made dams which fragment habitat.

While humans can somewhat mimic beavers by constructing BDAs, there is no replacement for the real thing; Beavers’ engineering work extends beyond the creation of dams. Within (and beyond) their wetlands, beavers dig canals and channels which allow the beaver to safely move through their wetlands without exposing themselves to land. Ecologically, these canals provide flood attenuation by carrying surplus water out of the main channel and into the floodplain where it can slowly seep into the soil. In concert with dams, beaver canals further reduce the erosive force of flood waters downstream, while simultaneously allowing more water to seep into groundwater stores (Fairfax & Westbrook, 2024; Burgher et al., 2025).

Beavers further alter the environment through the act of cutting woody growth, which they use for construction of dams and lodges as well as a food source. Removing trees from the riparian areas near the stream opens the canopy, allowing more light to reach the ground, and increasing plant diversity overall. In addition to the hydrophytic (water-loving) plants that thrive in wetlands, the open-canopy conditions induced by beaver activity allow photophytic (sun-loving) herbaceous plants to flourish.  

Overall, the presence of beavers increases ecosystem heterogeneity (a greater variety of habitats), which is key for preserving biodiversity. The wetland itself supports aquatic and wetland-dependent species of plants and animals that may rely on slower-moving water and saturated soils. The deep pools of the wetland provide habitat for cold-water adapted species of fish and provide refugia to other aquatic animals during periods of drought (Fairfax & Westbrook, 2024). Beaver wetlands also support pollinators, thanks to the open canopy; as compared to human-created wetlands, beaver wetlands possess a greater diversity and abundance of hoverflies, greater abundance of butterflies, and increased diversity of nectaring plants (Cook, et al., 2025).  

The effects of beavers on ecosystems apparently extend well past the wetlands and riparian areas. Beaver wetlands are associated with increased bat activity, which extends into the surrounding terrestrial habitat (Hooker et al, 2024; Moser et al, 2025). Similarly, increases in abundance and diversity of overwintering birds are associated with beaver wetlands as compared to non-beaver streams, and these effects extend into the terrestrial areas surrounding wetlands, for some distance into the forest (Fedyń et al, 2023).

Beavers certainly are experts at ecological stream restoration and wetland building, which is why Cincinnati Nature Center’s staff were thrilled to find evidence of beaver activity along Avey’s Run in 2023. While there was initially some trial and error in locating their dam(s), our resident beavers seem to have settled in to place and are hard at work building their wetland. In fact, the location the beaver chose is the site of a constructed (man-made) wetland, which had naturally filled in with rocks and sand over time. This resulted in a dramatic reduction in the area covered with water over the course of a few years.