By: Watershed Program Staff
The first telltale signs of beaver (Castor canadensis) activity at Ashbridge Preserve, found in late October, were chewed branches and a suspicious build up of twigs, branches, and other woody debris in Ridley Creek. Soon after, Watershed Program staff noted a slow, but steady, increase in the water depth in the riparian restoration area which could only mean one thing: the beavers had arrived in Ashbridge Preserve! Over the course of the next several months, beaver constructed four dams within Ashbridge Preserve, raising water levels throughout Ridley Creek.
The largest dam, visible upstream from [1] the stepping stone crossing, was the perfect candidate to place a game camera to watch the construction process. Almost immediately, the cameras picked up footage of a single large beaver, working tirelessly each night to build and repair the dam. Within the first several weeks, a second smaller beaver joined in the effort, carrying small twigs and branches, gently patting mud and leaves into the construction project, and generally getting in the way as all children do while learning how to help their parents. They worked together most nights to create a system of dams that have had a big impact on Ridley Creek during the driest fall in Pennsylvania history.
At the beginning of October, water depth in the riparian restoration area in Ashbridge Preserve had fallen to the lowest levels recorded on the EnviroDIY Sensor. No rain fell during the month of October, yet the EnviroDIY Sensor recorded a four-fold increase in water depth as a result of the construction of beaver dams in downstream sections of the creek (figure 1). A beaver’s dam building behavior can completely change an ecosystem: flooding forests, creating ponds, irrigating desiccated soils, and bringing life with each trickle of water. Beaver ponds that form upstream of a dam slow the rate of flowing water and flood the surrounding watershed area. This allows moisture to permeate more soil as the water level rises. As semi-aquatic herbivores, beavers live both on land and in water, and the engineering of higher water levels through the construction of dams provide easier access to food and less risk of predation, especially for young family groups. In periods of drought, like that which impacted the region in October, the increasing water level provides essential hydration for thirsty plant roots while also creating important refuges for aquatic and terrestrial wildlife alike.
Where beavers are active on the landscape, there is an increase in ecosystem biodiversity, wildlife abundance, and improved water quality. When beavers build dams, the ponding leads to more water entering the subterranean aquifer, which provides a critical resource during periods of low rainfall. Increased water retention supports environmental resilience, with hydrated soils and vegetation being more resistant to wildfires, storms, and erosion, and providing a safe haven for wildlife. While there is no guarantee that the family of beavers who called Ashbridge Preserve home this past winter will stay through the spring, the impact that they have had on the watershed will be long lasting.
