Responses of riparian plants to increases in habitat quantity and quality following restoration of channelized streams
(English)Manuscript (preprint) (Other academic)
We evaluated the ecological effects of stream restoration by comparing riparian vascular plant diversity and riparian habitat properties between channelized stream reaches and reaches restored with two different techniques in northern Sweden. Channelized streams were modified >50 years ago to facilitate timber floating which implied straightening and clearing channels from in-stream boulders and wood, which were deposited in riparian areas. Traditionally restored reaches underwent restoration efforts 8-10 years ago when material from the riparian zones was returned back to the channels. Some reaches were re-restored 3 years before our study by bringing large structural elements (boulders and downed trees) to the previously traditionally restored streams. These three restoration types (i.e., channelized, traditionally restored, and re-restored) represent a gradient in habitat complexity and we tested whether they also represent a gradient in plant diversity, and habitat quantity and quality. Riparian plant cover was higher at both restored types than channelized reaches. Responses of riparian plant diversity to restoration were scale dependent, with higher species richness at both restored types than channelized reaches at plot scale level (0.25 m2), whereas at the reach (>700 m2 of riparian area) and transect scales, plant species richness did not differ among the three restoration types. Differences in plots scale richness were largest in the most dynamic and species-rich part of riparian zones, i.e., at 20 and 40 cm elevations above the low summer water levels. We found no systematic differences in plant cover and species richness between the two restored types. Species composition did not differ among the restoration types at the reach scale, but at the plot scale species composition segregated between channelized and restored reaches but with small compositional differences between the traditionally restored and re-restored types. Aspects of both riparian habitat quantity and quality for vascular plants increased after restoration. Riparian zones along re-restored reaches had the highest amount of soils available for plant establishment in comparison to traditionally restored and channelized streams. In contrast, soil quality was more favorable to plants along channelized reaches, with higher soil pH and lower C:N ratio at some riparian levels. The magnitude of floods did not differ between the three types of streams, but inundation duration significantly increased following restoration with the longest inundation events at re-restored reaches. Thus, given that inundation is positively associated with plant species richness in riparian zones, habitat quality may have improved following restoration. We conclude that restoration of channelized streams has improved the abundance and diversity of riparian vascular plants. Given that we observed several positive trajectories in biotic and habitat recovery (although statistically insignificant in some cases) and that the new re-restoration technique is predicted to enhance riparian habitat conditions more effectively than traditional methods, we suggest that with time, further recovery of riparian vegetation may occur.
channelization, habitat quality and quantity, riparian vegetation, stream restoration, vascular plants
Research subject biology, Environmental Science
IdentifiersURN: urn:nbn:se:umu:diva-100216OAI: oai:DiVA.org:umu-100216DiVA: diva2:790794
FunderSwedish Research Council Formas