Humans are masters of ecosystem engineering. But so are many other creatures, not least among them: Beavers.
Paper Reference: Bouwes, N., N. Weber, C. E. Jordan, W. C. Saunders, I A. Tattam, C. Volk, J. M. Wheaton, M. M. Pollock. (2016) Ecosystem experiment reveals benefits of natural and simulated beaver dams to a threatened population of steelhead (Oncorhynchus mykiss) Scientific Reports. 6:28581. DOI: 10.1038/srep28581.
Online @: http://www.nature.com/articles/srep28581.pdf
When humans and beavers work together, the landscape, and the way it functions can change dramatically. These changes can in turn have a significant effect on other species as well. In a recent natural experiment conducted in John Day Basin in Oregon, USA, researchers measured the effect of human encouraged beaver activity on steelhead fish populations (an endangered species). The results, published in Nature’s Scientific Reports, suggest that as beavers change the way water moves through the river system, they in turn create abundant habitat for the spawning steelhead fish. The fish move into these spaces and their populations grow almost immediately after the beavers take over.
This study builds on previous work that has demonstrated the effect beavers can have on river systems. In particular, beavers do three important things to effect these changes, first: beavers build dams. When beavers are encouraged to build on stable structures — or “fake” beaver dams constructed by humans (called beaver dam analogs (BDAs) in the article) — they happily oblige, moving in and taking over further construction. Second: beavers also dig canals to transport the woody vegetation they harvest off the landscape. This helps lead to complex and diverse networks of pools and water cascades that are not otherwise present in the river system. And, third: beavers are notoriously busy. This means that only a small amount of encouragement is needed before beavers move into new territory and take over the work of reclaiming a stretch of river.
The study hypothesized that these different characteristics of beavers would, given a little help and little time, result in a stable reconnection of a previously eroding or incised stream with its adjacent floodplain. Further, the study authors hypothesized that all the beaver activity was creating ideal fish habitat, and steelhead (an endangered species), would return and thrive.
To test their hypotheses, the researchers utilized seven years of observational data collected before and after human encouraged construction of beaver dams in two watersheds. They monitored the study area before and after the intervention to assess the ecosystem response across multiple dimensions, both physical and biological. Observed changes were compared to stretches of river that were not disturbed by humans or beavers.
Beavers have a dramatic impact on the places they chose to live. On the one hand these changes are physical. For instance, the complex network of dams and pools of various depths creates greater water retention on the landscape. This water retention means water has time to seep into the ground recharging groundwater reserves. When summer river flows get low, that stored up groundwater becomes a source of water for the river, and moderates stream flows so they stay more consistent. When the water flow is more uniform over seasons, the temperature of the water in the river exhibits fewer spikes which would otherwise be a source of biological stress.
These physical changes are welcome news for the steelhead fish. The recaptured floodplains and deeper pools means there is a variety of environments for fish to choose from depending on their age and needs. While the reclaimed flood plains might be good for very young steelhead to find food and shelter from predators, deeper pools might be best as the fish grow or the water temperature warms in the summer.
Perhaps most surprising, the authors were not concerned with the change in the number of beavers present in their study area. They cited the intelligence of beavers to avoiding traps as the primary reason for not tracking this particular change. Crafty beavers!