Effects of climate change and restoration on stream-side vegetation in boreal forest landscapes
Riparian areas along streams and rivers in northern Sweden are hot spots of plant species richness, especially in comparison with the matrix vegetation of boreal forests. The hydrological regime of the flowing water regularly disturbs the river banks and is one of the most important drivers of riparian plant dynamics. Riparian vegetation is highly sensitive to changes in flood frequency and duration as well as changes in base flow.
Climate change in northern Sweden is expected to lead to earlier and smaller spring flood peaks, higher flows during winters and potentially autumns with larger frequencies of high flow events. Reduced spring floods will leave parts of the riparian forest zone unflooded, where most plant species are found, potentially leading to species loss. Higher winter flows may also eliminate amphibious plants dependent on lower winter than summer water levels that leaves ice stranded in the riparian zone.
In the past, a large proportion of the streams in northern Sweden were channelized to facilitate timber floating. River channelization increased flow velocity, resulted in more flashy hydrographs and generally disconnected riparian areas from their rivers. Restoration entails removing stone walls blocking backwaters and side channels, replacing stones, boulders and logs back into the channel, and increasing channel sinuosity. This increases channel roughness, reduces flow velocity, and increases the duration of high flows. Such restoration measures have proved effective in increasing habitat availability as well as abundance and species richness of riparian plants, but their function in a future climate is not known.
The goal of this project is to understand how climate change and ecological restoration will interact to affect the riparian vegetation along medium-sized boreal forest streams in northern Sweden. Using knowledge about riparian vegetation-flooding relationships, plant responses to ecological restoration and modeling of future hydrology, this project will test whether ecological restoration of streams can be an effective way to increase the resilience of riparian zones to climate change.
Riparian vegetation along channelized (to the left) and restored (abowe) streams in northern Sweden. Effect of changed hydrology in future climate is predicted along these streams.