The importance of different scale processes for the restoration of floodplain woodlands

The restoration of floodplain woodlands demands an understanding of the linkages between process, form and past management history at both a local and catchment scale. Site and reach scale processes that influence the species composition of floodplain woodland species are described with a particular focus on the relationships between hydrological and sediment inputs to floodplains and the regeneration response by tree species. The importance of integrating natural science knowledge gained at the site reach scale with decisions taken at the catchment scale on water allocation priorities is then discussed. Research was carried out on the River Ore in Sweden, The River Ouse in the United Kingdom and the River Isere and River Garonne in France. Research results at the site and reach scale allow broad definition of ideal conditions for the regeneration and growth of floodplain tree species and the flows that provide them: (1) channel movement has to occur for the creation of sedimentation sites required for the regeneration of early successional species and the flows that provide them; (2) flooding events should occur periodically to cause both channel movement and recharge floodplain water tables; (3) water table decline rates following a flood event must be slow enough that seedling roots can maintain contact with the retreating water front; (4) unseasonal flood events can cause high mortality of seedlings and prevent successful regeneration in any season. Some of the requirements for the restoration of floodplain woodlands can be delivered through site and reach scale restoration projects with reasonably predictable ecological outcomes. A more holistic approach to the provision of regeneration sites for floodplain woodlands would also include water allocation decisions targeted at providing flow conditions which could restore geomorphological processes. However, it is difficult to predict ecosystem responses to catchment scale flow allocation measures and, therefore, in the intensively managed river corridors of Western Europe, river restoration initiatives tend to be restricted to the site and reach scale.