The Ultimate Gardener: Do beavers plant willows in the wild?

Cecilia Alstrom-Rapport, assistant professor in the Ecosystem Science and Management Program at the University of Northern BC, accompanied me to the Aleza Lake Research Forest for a day last May to tour some of our finest beaver dams...and we have plenty. She was looking for an additional study site to expand her field project on the interaction between willows and beavers. On our third dam we hit the mark; the beavers had used an old road in the southwest corner of the forest to dam a seepage area along the ditch line. There were signs of recent beaver activity and plenty of willows around. Perfect.

Cecilia, along with her student assistants, started the project in 2005 as a genetics study on willow reproductive ecology in British Columbia lowlands, collecting data on pollination (insect and/or wind pollination), suckering, and male/female ratios. Willows are an important component of many plant communities in the northern hemisphere providing food and shelter to wildlife such as moose and beavers. Many are pioneering species, establishing early after disturbances like forest fires and on river floodplains. This study, funded by Aleza Lake Research Forest Society and Natural Science and Engineering Research Council of Canada grants, aims to use genetics to understand the life-history, reproductive characteristics and distribution of willows.

A problem emerged in these creekside study sites. The beavers kept cutting down Cecilia's sample bushes and dragging them away. Beavers rely on willows for food and for building dams and lodges. Thirty-eight of the sample willows were so heavily browsed by beavers at one of her study sites at Aleza that either their tags could not be found or no remaining branches could be used for species identification. Our staff at the Research Forest got into the habit of finding and sending these tags back to Cecilia after cleaning out a road culvert that a resident beaver persistently tried to dam using her research samples.

But give Cecilia lemons, and she makes lemonade. Now, she is launching a related study on the role of beavers in the reproduction and distribution of willows.

Hence, the dam tour.

The beaver-willow interactions are proving to be an important factor in reproduction. Cecilia and her field crew have found that in several of the study locations a portion of the branches cut by beavers were dragged along the shore but then abandoned. Many of these branches established as new plants. Consequently, beavers appear to have an influence on the genetic distribution by spreading willows around. Along larger rivers, branches cut by beavers could travel tens to hundreds of kilometers establishing new individuals that are genetically related to those upstream. Therefore, beaver browse may not only influence the local genetic structure but may also be important for downstream willow migration.

This summer, Cecilia and her research group will be tagging sample willows at the new beaver dam site. When I told her we may need to replace a culvert at one of her sites which could disrupt her current study, she didn’t blink an eye…”Hmmm, maybe we can do a ‘before’ and ‘after’ study when you do that”…keep making that lemonade Cecilia!

Sources:
Cecilia Alstrom-Rapaport. 2006. Reproductive Willow Ecology along the Bowron River. Unpublished ALRF Research Report.