RiverWood

River woods include trees and wood in the riparian zone, floodplain and on the hill slopes. They form many kinds of woodland habitat, such as:

• Riparian woodlands are transitional environments between land and water ecosystems that are found along the bank or in a body of freshwater, such as a stream, river or lake. Among their important functions are temperature regulation, bank cohesion and organic inputs, such as leaf litter that drives food web dynamics.
• Alluvial woodland lies within a fluvial floodplain subject to regular or natural flooding. This includes woodlands on islands within a river.
• Gorge woodland occurs where riparian trees growing on steep banks or slopes over rivers or streams act together to produce high humidity levels and to provide for development of lush vegetation, including epiphytic species.
• Riparian buffer strips are managed woodland next to freshwater which typically acts as a 'buffer' to agricultural land, moderating its impact on the adjacent waterbody.

Another key function of riparian woodlands is the supply of large wood (LW) into the channel. LW provides crucial benefits to river ecosystems by creating complex habitats for stream biota, by acting as a food source for invertebrates, by stabilising riverbanks and riverbeds and by serving as perches for birdlife along rivers.

LW creates complex flow patterns, which in turn lead to the formation of pools and riffles. These habitat features are critical to the life cycles of salmonid species, and LW also provides cover and refuge for fish and other stream biota from predators and during high flows. As the wood decomposes, it releases organic matter and nutrients, further supporting the food web.

RiverWood Project Aims & Goals

Inland Fisheries Ireland are working with University College Dublin to evaluate the functional relationships between riparian zones and LW in rivers. The RiverWood project aims to quantify the role of LW in the provision of complex habitat and other services and to provide an evidence base for the protection and restoration of rivers in Ireland. This project is funded by the Environmental Protection Agency Research Programme 2021–2030.

The core objectives of RiverWood are:

1. To capture the current state of knowledge on riparian zone and LW functional relationships
2. To synthesise information and drivers for existing LW management strategies in Irish rivers
3. To assess the efficacy (biological response, cost & sustainability) of LW augmentation as a protect and restore tool for key species, habitats and their ecosystem services
4. To synthesise information and drivers for existing LW management strategies in Irish rivers
5. To produce a guidance tool that will support future management of riparian zones and LW in Irish rivers

Large Woody Habitat in River Restoration

LW reintroduction is increasingly used in river restoration projects to kick-start more natural river processes and thus to conserve or recover biological populations. In Ireland, however, there are few such projects and little collected evidence documenting the assumed biodiversity gains.

To close this knowledge gap, RiverWood will document the ecological and geomorphological effects of large wood on riverine habitat and instream biota at several demonstration sites where LW is naturally present instream or has been installed as a protect-and-restore measure.

Examples of large wood reintroduction. Selected trees are felled and anchored to provide cover and nursery habitat for juvenile fish. This mimics natural treefall and recruitment of large wood into the river.

Supporting Best Practice and Policy Development in River Management

The RiverWood project partners recognise that the eventual success of restoration strategies that use LW will depend on the extent to which scientific evidence is conveyed effectively to policymakers and on public support for decisions made.

Alongside providing the evidence base for the potential benefits of LW to habitat quality, RiverWood will seek to capture the socio-ecological context and the public perceptions and experience of instream LW because of perceived flood risk and potential conflicts that may arise with its use as a restoration tool. This underscores the importance of providing scientific evidence to support policy decisions and to increase awareness of the ecological significance of LW in river systems for key species.

Hydromorphological processes: a riffle feature suitable for salmonid spawning has formed following the reintroduction of large wood. The large wood traps gravels on the upstream side to promote development of the riffle habitat.

RiverWood project partners: IFI, EPA & UCD