Nationwide study: Forests along rivers improve ecological condition

There is increasing evidence that forested riparian corridors improve the ecological status of freshwaters, but this Finnish study takes one step further and looks at the effect on a national scale. The scientists used data from more than 900 river water bodies in Finland.

They found that the ecology of small to medium sized rivers in an agricultural landscape benefitted most from forested riparian zones. The ecological quality increased by almost one status class when the riparian forest cover increased from 10 % to 60 %.

Riparian forests are especially beneficial for the ecological status in small agricultural headwater streams. Photo: Mikko Tolkkinen

For large rivers, the authors did not find the same effect of adjacent forested land. Here, the land use and management practices in the entire catchment probably plays a larger role than the land use closest to the river course. The fact that large rivers did not respond the same way as smaller headwater streams does not mean that forested buffer zones are not beneficial also for these water bodies, merely that the clear pattern found in smaller streams was not that obvious. Moreover, protecting and restoring headwater riparian zones are likely to have advantages for ecological quality further downstream as well.

The authors emphasise the implications of this study for managers that strive to achieve the EU Water Framework Directive (WFD) goal of good ecological status of rivers. The results demonstrate how forested riparian zones can have an independent positive effect on the ecological status of rivers. Therefore, forested buffer zones should be more strongly considered as part of river basin management.

Tolkkinen, M., Vaarala, S. & Aroviita, J. The Importance of Riparian Forest Cover to the Ecological Status of Agricultural Streams in a Nationwide Assessment. Water Resour Manage (2021). https://doi.org/10.1007/s11269-021-02923-2

(Feature photo: Eva Skarbøvik)