Monday, October 20, 2008

Wildlife need wildlife-friendly habitats? REALLY?!?!

New research out of UC Davis shows (basically) that when some place looks good to humans doesn't mean that it's good for wildlife. This is one of the problems with restoration, whether it is terrestrial or aquatic. This past weekend, I was able to take a trip with a University of Michigan graduate class to the DNR fish hatchery in Oden, MI, which had a stretch of a restored stream (photo looking downstream)

The stream used to be a concrete-lined channel that went from the hatchery (upstream of the photo) to the river, maybe one mile downstream. Apart removing the concrete and replanting the floodplain, the stream was designed to be "encouraged" along its path, thanks to a series of log-hardened banks lining the bank facing upstream. The stream setting looks quite natural to the eye - a floodplain vegetated by grasses and mosses with a stream running down the middle. The place is engineered to look (to human eyes) like it is a perfect place for fish habitat. It cries out to our own human ideas of how a small creek should look like in the Upper Midwest. Looking into the creek, a person sees a gravel bottom, riffles and pools in fast-moving water, both perfect for trout. However, these beautiful-to-the-eye characteristics of the system are quickly shown to be merely gussied-up stream-porn. After conducting a few invertebrate samples of the region turned up a very low diversity of insects, especially considering what one would expect to find in such a setting (if it were truly natural).

Part of this low diversity can be explained by the fact that all of this is below a fish hatchery, which are known for producing high-nutrient waters. However, this is surely not the whole story. I'm not personally sure as to why there was such a limited diversity of invertebrates in the area, especially since one might expect a high level of algal formation due to the presence of such high nutrient levels. However, grazers (other than isopods) were largely absent from the sample. Similarly, even isopods were not highly abundant, making the area not only have a surprisingly low diversity (surprising only if you had no knowledge of the hatchery upstream of the apparently natural site), but also a surprisingly low biomass. Some of this might be explained by the following: due to the low diversity of organisms, fish present in the stream feed heavily upon isopods and amphipods, thus diminishing their overall abundance; this predation has little impact on increasing the biodiversity since conditions are not good for maintaining a highly biodiverse system to begin with. I don't know if this is true, but on the face of it, the so-called restored stream doesn't seem to provide a good source of food for fish living outside the hatchery, while making it look "nice" for people.

However, even this latter point is one of potential contention, since the system does not seem to have been engineered appropriately. The design of the stream system appears to be too narrow for the amount of discharge it receives, and some of the log-reinforced banks are being under-cut. Rivers are, after all, dynamic systems, and forcing it along a pre-determined path using logs which are effectively perched on sand is not likely going to create a lasting system. Examining even a portion of the system showed places where the stream had cut into the bank to go around root systems, cut under logs (anchored into the stream bank) to effectively "straighten" itself, and the like. Perhaps the design firm wanted to make the system look naturalized to the eyes of humans faster than the stream wanted. To put it another way, I feel that the design firm removed a concrete channel and created a surrogate out of logs and gravel. Although it looks natural, it isn't really so.

However, one great aspect of this resoration process was the creation of a fish-viewing room where one can look immediately upstream and downstream of a plunge pool, and see how the fish utilize that area of habitat to their advantage.

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