Impersonating Beavers
A couple weeks ago, Defenders of Wildlife volunteers joined the Santa Fe National Forest, Trout Unlimited, and New Mexico Trout in the Jemez Mountains west of Santa Fe for a day of ecological restoration.
We were building Beaver Dam Analogs (BDAs) along the Rio Cebolla in the Santa Fe National Forest to improve local vegetation, repair wetlands damaged by overgrazing, and improve habitat for a litany of aquatic and terrestrial species including the endangered New Mexico meadow jumping mouse.
The New Mexico meadow jumping mouse, listed as endangered in 2014, lives in alpine riparian areas and relies and good grass cover near streams for its nests and for protection from predators. As the BDAs help regenerate wetlands that have become channelized from logging, overgrazing and other impactful historic uses, the grasses that come back will provide habitat that will be necessary for this species to recover.
The theory behind BDAs, which are relatively new to the world of ecological restoration, is that they mimic the ecological benefits of real beaver dams and help recruit actual beavers to continue the good work that these structures facilitate. As water is impounded, willow fill in the banks providing a sustainable food source for the beaver’s eventual homecoming as well as shade to cool the water for cold-water, loving fish like the Rio Grande cutthroat trout.
Before we arrived, the Forest Service had driven-in ponderosa pine posts in lines across the small stream at 10 different locations. They had also cut a number of willow poles that were kept wet (and pliable) in the stream.
As volunteers, our job was to weave the long willow poles through the ponderosa posts and compact them to create a dam effect. As we tightly wove the willows into these structures, we also used rock to seal any holes on the bottom and sides of the stream bed so that the water couldn’t erode its way around the dams.
Every structure varied, but most took about an hour to build with two-four people working at each site. What was most amazing about them was that we could see the structure work in real time. Very quickly, the water behind the dams rose and spread-out, rewetting areas that had previously been dry.
As the BDAs continue to trap sediments over the coming weeks and months, they will become even tighter and better sealed meaning that downstream, the water will remain clearer, and eventually, the water will rise to the point that it will pour over the willow poles.
The best part? Because all of the materials are natural and native to the area, if and when the dam eventually collapses, rots or erodes, we can take comfort in the fact that we are not adding anything to the ecosystem that doesn’t already belong.
- Michael
