Poster Presentation Society for Freshwater Science 2025 Annual Meeting

Aging beaver impoundments using growth rates of standing softwoods (118963)

Kendal Massey 1 , Abigail Hullihen 1 , John Donnelly 1 , Emily R Arsenault 1
  1. Environmental Biology , SUNY ESF, Syracuse, New York, United States

The North American Beaver (Castor canadensis) changes its landscape by felling mainly hardwood trees, creating impoundments to moving water that result in lower energy systems that flood surrounding areas and decrease the growth rates of impacted trees. These impacts are episodic and cyclical, with dams typically standing for one or more decades. Therefore, reconstructing the history of beaver influence in a system over time can be important for understanding long-term ecosystem function. Commonly used methods to age beaver impoundments involve the removal of wood from dam structures, which is destructive and not possible in sensitive systems. Here, we propose and test a non-invasive way to estimate timing of flood events by aging beaver impoundments using dendrochronology on standing softwood trees. In an Adirondack hardwood forest where beaver activity has been tracked for over 70 years, we sampled three beaver ponds over an age gradient, from intact dams to breached dams, to historically dammed reaches. We then estimated flood timing for one stream with a breached dam of unknown age. At 150-meter increments, transects were surveyed to obtain tree species and crown class information (n=45). In these riparian zones, softwoods were cored along both high- and low-energy segments of stream. Cores were then analyzed using skeleton plotting to determine years of decreased growth. There was a statistically significant difference in the proportion of softwood trees between low-energy (71% softwood) and high-energy (37% softwood) reaches (p=0.004). A distinct pattern was seen when comparing skeleton plots from high-energy to low-energy sections of the stream with unknown beaver impoundment ages, implying two major damming events: one in the early 1930s and one in the late 1990s. Preliminary results indicate a new potential method for determining the hydrological history of streams and their riparian zones in systems engineered by beavers.