New research led by SLU in collaboration with Stockholm and Karlstad Universities shows that the effects of forestry on boreal streams extend far beyond the harvested areas, impacting water temperature and aquatic organisms downstream. The results highlight the need for wider riparian buffer zones to protect freshwater ecosystems and for landscapes scale planning.
The research results, published in Water Resource Research and the Journal of Environmental Management, show that clearcuts can raise stream temperatures by up to 4.1°C in summer, with these temperature increases persisting at least 150 meters downstream in streams with riparian buffers that are narrower than 10 m on each side of the stream. “We’ve long known that clearcutting can heat up streams, but our research shows that these effects don’t just disappear at the edge of the harvested area, they continue downstream, even if the stream enters a forest again” says Caroline Greiser (SU), one of the lead authors. “Importantly, clearcutting did not just affect water chemistry and temperature - it also disrupted the fundamental energy flows that sustain aquatic life” explains Maria Myrstener (SLU), the second lead author.
These studies provide clear evidence that 15-meter buffers are the minimum needed to protect streams from clearcutting impacts but importantly they reinforce the importance of rethinking riparian buffer guidelines in boreal forests. Many existing forestry policies focus on protecting streams only within the harvested area, without considering how far downstream the effects can spread. This new research also shows that at any given time, up to 57 000 km of waterways (1.4 times around the equator!) in Sweden is somehow affected by clearcutting, either locally or downstream.
“I have been studying riparian buffers for 7 years and these result on downstream propagation really concerns me “, says Lenka Kuglerová, the principal investigator on the Formas funded project. To maximize the effectiveness of riparian protection, a landscape-scale strategy is necessary, ensuring that upstream conditions do not undermine local protection efforts. The researchers emphasize that adopting wider and strategically placed riparian buffers will not only benefit aquatic biodiversity but also help meet national and EU water quality goals under the Water Framework Directive.
