I spent three days in eastern Oregon volunteering with ONDA (the Oregon Natural Desert Association), helping to build beaver dam analogs. These are human made structures which act like beaver dams. I knew that there weren’t many beavers now in the west and that it was due to trapping in the past but didn’t know the full story.
Beavers were wiped out In the Pacific Northwest about 150 years ago as a deliberately and consciously evil plan by the Hudsons Bay Corporation to create a “fur desert” (their words). In other words, they didn’t just trap some of the beavers and leave some to grow and repopulate (as would be a typical strategy), they trapped them ALL along with all other fur bearing animals. I cannot express how evil this seems to me. You can read more about this in research by Jennifer Ott at: https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=2828&context=etd
The loss of beavers had severe and continuing consequences to the desert west. Streams and rivers which used to make broad fertile flood plains now gushed in steep sided streambeds with only a narrow strip of riparian vegetation. Groundwater levels in the former floodplain dropped and the cottonwood trees and willows died. Without beaver dams to trap sediment the sediment ran off into the stream then to the rivers, ending up in the ocean. Sediment in streams is bad for many reasons- one is that it coats the gravel beds that fish lay eggs in and kills the eggs.
So, what to do? When beavers do move back into streams and rivers the process of downcutting slows and reverses. But beavers have a difficult time in places where they where they once were for two reasons- the first is that the vegetation beavers eat is scarce- the second is that the dams that they build in these steep sided downcut streams get blasted out during floods. But humans can help by building what is called a “beaver dam analog”.
This is a dam made from poles driven into the stream bottom with branches woven around them. We (16 people all told) made 24 dams in three working days.
Before we started working, ONDA’s riparian ecologist gave us an inspirational tour. ONDA has been building BDAs on this creek for 2 years. The differences between stretches with BDAs and without were stark. Behind the previous BDAs theres was water and green, otters and birds.
Where there were no BDAs in the creek the soil was often eroded down to bedrock.
Here’s a BDA we built.