Looking beyond boulders and logs in boreal stream restoration

Our new latest issue features the article, Differential responses by stream and riparian biodiversity to in-stream restoration of forestry-impacted streams by Turunen and colleagues. Here, Associate Editor, David Moreno Mateos shares his views on the challenges of stream restoration.

Stream restoration is just not possible today. At least, if your plan is to just drop a bunch of rocks or logs into the creek. Turunen et al. report in their study that over a three to seven year period after restoration, adding boulders or wooden structures did not motivate a comprehensive response of the stream ecosystem. I mean comprehensive, but they did find particular and quite different responses to each action. Boulders left more room for aquatic plants, well bryophites, by reducing the area covered with fine sediments, and wooden structures had an interesting cross-boundary effect on riparian vegetation, by restoring the retentiveness and thus facilitating the settlement of forbs rather than grasses.

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One of the streams restored with boulders, although logs from forest management are also falling in. (Image: Jukka Aroviita).

It is true that three to seven years is a rather limited timeframe to evaluate ecosystem recovery, but it is interesting that they found weak or no effects on the macroinvertebrate and decomposing microbe communities and related ecosystem functions (periphyton accrual and leaf breakdown). This may indicate that plants go first and that components requiring a deeper restructuration of the ecosystem architecture may need more time. The next question is how long does it take? The eternal question that never receives a response.

By ‘a deeper restructuration of the ecosystem architecture’ I mean the structure that emerges from the interaction among organisms or between organisms and the environment. For example, restoration of the macroinvertebrates community is required to restore the feeding resources, which can only recover if we have succeeded to restore the terrestrial and aquatic plant communities in the very first instance. Then this plant structure must accumulate the required amount of resources to even allow the settlement of an initial macroinvertebrate population. Another example, to restore the soil microbial community responsible for leaf-decomposition, again we need to restore the plant community and, again, allow it to accumulate enough resources to sustain a microbial community that itself must find its own recovery path. In any event, yes, this sounds like a time issue (among other things), but that’s the thing, we need to shorten that time.

Going back to restoration, this paper is again telling us that restoration is not one action or a once-in-time thing. Please, remember that, it is not. Turunen et al. are saying that putting boulders is not working, that putting logs is not working, and that even putting boulders and logs is not working. I would add that adding organic material, revegetating, removing pollutants, or reintroducing species are not working. The point is stream restoration is an extremely complex endeavor and thinking that you can get anything restored just by combining a few of these actions in a once-in-time intervention is fantasy. My advice, if you still think that way, quit tonight.

In the end, Turunen et al. are telling us that we need to be way more creative in planning stream restoration. If I had the chance to re-restore their streams I would add logs to streams with boulders, and vice versa. I would see what the macroinvertebrate and microbial communities look like in undisturbed streams and try to find what they need to live there that is clearly missing in the impacted streams. This is basically what restoration is about, right?

Differential responses by stream and riparian biodiversity to in-stream restoration of forestry-impacted streams is available in issue 54.5 of Journal of Applied Ecology.

One thought on “Looking beyond boulders and logs in boreal stream restoration

  1. I don’t think we should be talking about re-restoration (i.e. going in and restoring these sites over again as they have done in some Swedish streams), but experimentally trying something else, somewhere else, while we give these streams more time to recover. Maybe we’re just being too impatient? It can take more than 25 years for riparian zones to recover biodiversity and N cycling in larger boreal streams (Hasselquist et al. 2015, 2017), at least with older restoration methods.


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