Suitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20-40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature-sensitive species from climate warming. # Crown copyright 2010.

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[1] The U.K. Government's 1995 White Paper on Rural England [Her Majesty's Stationery Office, 1995] proposed a doubling of the area of woodland within England by the year 2045. Questions were later raised concerning the possible impacts on water resources of such a large change in land use. This paper presents results of field study investigations of the water use of grass, heath, oak, and pine vegetation at Clipstone Forest, Nottinghamshire, United Kingdom, which were used to calibrate the water use model HYLUC and derive predictions of the impact of different vegetation types on recharge in this locality. Average annual recharge plus runoff (millimeters) over a 32.5 year period and the uncertainties due to spatial sampling, calculated with the HYLUC model, were 136 ± 11 for the grass site, 122 ± 3 for the heath site, 76 ± 5 for the oak site, and 34 ± 8 and 38 ± 3 for two pine sites. In this region of Britain the long-term recharge beneath pine is approximately one quarter that under grass and essentially only occurs in years of above average rainfall. Oak woodland is also predicted to have a significant impact by reducing recharge plus runoff by almost one half as compared with grassland.

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Natural flood management (NFM) is the use of natural processes and environments to mitigate flood risk by reducing and delaying peak flood. This review introduces the concept and history of NFM and looks at the current state of research into the potential for using different types of woodland to fulfill the aims of NFM. Four woodland types (catchment, cross-slope, floodplain, and riparian) are discussed with reference to studies carried out, mainly in the United Kingdom, to determine the relative merits of each type and their effectiveness in mitigating flood risk. We then discuss how trees interact with the hydrological cycle, along with a discussion of modeling methods which seek to determine the amount of water intercepted by different types of forest cover. We find that while there is some evidence that carefully planned and managed woodland can mitigate flood risk, the published data for this evidence base is somewhat sparse. This may be either due to the long timescales needed for comprehensive studies or the relative infancy of the research on NFM. More research needs to be carried out in each of the four woodland types, especially in the UK, as policy makers are increasingly looking towards nature based solutions to mitigate the potential impacts of climate change. The concept of a combined canopy/hydrological model which can be scaled from stand to watershed level and incorporate different types of woodland is suggested as it would be beneficial in guiding woodland creation policy in the future, both at the local and regional scales.