Differential responses by stream and riparian biodiversity to in‐stream restoration of forestry‐impacted streams

Abstract

Summary Forestry can have detrimental impacts on stream ecosystems, particularly via excessive sedimentation. A key challenge to stream management is therefore to identify the best restoration practices to mitigate the harmful impacts of fine sediments on stream biodiversity and ecosystem functioning. We studied the effects of restoration of sediment‐impacted headwater streams on the habitat structure, hydrologic retention, biodiversity (microbes, bryophytes, benthic macroinvertebrates, riparian plants) and ecosystem functions (periphyton accrual rate and leaf breakdown) by comparing four treatments: wood‐restored, boulder‐restored, impacted (by fine sediments) and near‐natural streams. The restored streams were sampled 3–7 years post‐restoration. Restoration by wooden or boulder structures aimed to reduce deposited sediments and increase channel heterogeneity and hydraulic retention. Wooden structures were ineffective in removing fine bed sediments and did not induce positive responses in aquatic biota. Boulder additions reduced substrate limitation and thereby proved beneficial for aquatic bryophytes. Benthic macroinvertebrates were clearly impaired by sedimentation but responded weakly to restoration. Leaf‐decomposing microbes and ecosystem functions were unresponsive to restoration but neither did they differ between near‐natural and impacted streams, suggesting that they were little harmed by sedimentation. Wood addition enhanced hydraulic retention, and riparian plant assemblages along wood‐restored streams resembled those in near‐natural streams, suggesting that increased retention re‐established a more natural flood regime. By contrast, riparian plant assemblages in boulder‐restored streams did not differ from those in impacted streams. Synthesis and applications. Restoration improved several aspects of stream and/or riparian biodiversity, but had limited effects on ecosystem functions. Different restoration measures resulted in differing biodiversity outcomes: boulder addition was more effective at restoring in‐stream heterogeneity and aquatic biodiversity, whereas wooden structures helped restore channel hydrology and retentiveness, and, consequently, riparian vegetation. Therefore applying both measures in the restoration of forested headwater streams with naturally stony substrates enhances stream habitat variability at the watershed scale, providing the most promising scenario for biodiversity benefits in broad‐scale restoration designs. In‐stream restoration that increases hydraulic retention has impacts that extend beyond ecosystem boundaries, reinforcing the need to restore, manage and protect streams and their riparian forests in an integrated effort.

Restoration increases transient storages in boreal headwater streams

“…Boulder‐based restoration seems to be more effective than wood‐based restoration at restoring benthic habitat structure in sediment‐stressed streams, with benefits for the recovery of in‐stream biota such as bryophytes and benthic invertebrates (Turunen et al, ). However, wood‐based restoration changes riparian plant communities towards those of natural streams, suggesting changes in riparian soil moisture and flood regime (Turunen et al, ). Individual wooden structures (Tammela et al ) may be effective for only a few meters from the structure, creating localized transient storage areas.…”

“…These results emphasize the need to combine multiple measures in the restoration of headwater streams, because different restoration methods had different effects on stream TTS and bed substrate characteristics. Additionally, boulder versus LWD restoration have divergent impacts on stream biota (Turunen et al, ). The restored streams had less added wood than in pristine conditions, and we recommend using more LWD in headwater stream restoration.…”

“…Increased sediment deposition to stream beds from human alteration of catchment land use is a global concern and poses a particular challenge for the restoration of headwater streams with limited sediment transport capacity. Headwaters form ecotones with their terrestrial surroundings and often support unique elements of regional biodiversity (Turunen et al, ). Because of their intimate links with the surrounding catchment, headwater streams are highly sensitive to anthropogenic land use stressors.…”

Macroinvertebrados como bioindicadores em riacho tropical: uma avaliação de impactos por sedimentação, rompimento de barragem e de recuperação após medidas de restauração

“…Nela é possível observar que a maioria dos estudos, como citado no parágrafo anterior, objetivam o reestabelecimento da heterogeneidade de habitats pela implantação ou substituição de substratos, construção de estruturas, escavamento e inserção de pedras e pedregulhos para a formação de rápidos e poças, mudança da morfologia dos canais e na corrente, sendo que tais condições são esperadas para um ambiente natural. No entanto, ao analisar as respostas da comunidade de macroinvertebrados (Tabela 3), verifica-se que a implementação dessas ações não trouxe efeitos significativos, segundo os resultados apresentados pelos autores, mesmo considerando que em boa parte dos estudos tenha passado tempo suficiente após a implementação dos projetos para reestabelecimento da comunidade (FRIBERG et al, 1998;LAASONEN;MUOTKA;KIVIJÄRVI, 1998;LEPORI et al, 2005;LOUHI et al, 2011;SUNDERMANN et al, 2011;TURUNEN et al, 2017). A utilização dos grupos funcionais alimentares também apresenta-se como uma efetiva ferramenta na avaliação desses projetos, conforme destacado por Lakly e McArthur (2000), as mudanças nesses grupos podem indicar a recuperação de riachos perturbados, ao qualificar as diferenças no funcionamento do ecossistema recuperado de outras áreas controle.…”

“…FRAINER et al, 2017, JANUSCHKE et al, 2014LOUHI et al, 2011;LÜDERITZ et al, 2011;MUELLER;PANDER;GEIST, 2014;SUNDERMANN et al, 2011;TURUNEN et al, 2017) enquanto que para países da América do Sul esses projetos ainda são escassos. A sua aplicação pode ter diversos objetivos, destacando-se que a implantação de projetos que visem a restauração de habitats tem aumentado, buscando facilitar a recuperação da biodiversidade e do funcionamento dos ecossistemas dos ambientes degradados (FRAINER et al, 2017).…”