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Forest buffer in Baltimore County, Md.

In the United States, society spends billions of dollars each year on stream restoration. Knowing where restoration efforts are likely to be most effective could help get more restoration-bang for those bucks. A recent study of 13 river restoration projects by investigators from the Baltimore Ecosystem Study LTER found that restoration appeared to be more effective at supporting increased biodiversity in isolated headwater streams than in more connected mainstem reaches.

The study, published in Ecological Applications, was designed to test a basic tenet of metacommunity theory—that is: when is dispersal more important than local environmental conditions in determining the makeup of a given plant, animal, or microbial community? The theory is difficult to test because dispersal happens at relatively large scales, while local environmental conditions are, well, local. But stream networks constrain the spread of aquatic organisms and restoration projects offer a ready-made controlled experiment with treated and untreated conditions.

The researchers measured the diversity of invertebrate communities in restored and neighboring unrestored stream reaches and found that restored headwater reaches harbored on average 28% greater taxon richness than unrestored headwaters—while mainstem reaches showed very little difference between restored and unrestored conditions. Their observations support the idea that in well-connected streams (and possibly other landscapes), dispersal may be more important than habitat quality in controlling what species take up residence.

Even in densely populated cities, healthy streams support flood control, water quality, offer recreational opportunities, and help build an intimate connection to nature. Biodiversity isn’t the only reason to restore streams, but when it is the goal, ecological theory can help inform choices about when, where, and how to restore.

Swan, C. M. and Brown, B. L. (2017), Metacommunity theory meets restoration: isolation may mediate how ecological communities respond to stream restoration. Ecol Appl, 27: 2209–2219. doi:10.1002/eap.1602