Anthropogenic climate change is inducing large-scale changes in rainfall intensity and frequency with a concomitant rise in flooding globally. Increasing ecological complexity through the integration of trees into the landscape creates multifunctional landscapes and can provide opportunities for ‘natural flood management’ through the regulation of streamflow. Whilst there is strong evidence to demonstrate an increase in streamflow from deforestation, evidence of a reduction in peak flow following afforestation is unclear due to a lack of empirical research. Moreover, the role of trees in hydrological regulation outside of forests, such as hedgerows, are little studied and often excluded from ecosystem service models. This thesis aims to understand tree species identity, richness and soil type on hydraulic function as well as the role of hedgerows in regulating soil water and the interaction with soil type, hedgerow age and time of year. Seven broadleaved tree species (Alnus glutinosa [L.] Gaertner, Fraxinus excelsior L., Fagus sylvatica L., Betula pendula Roth., Castanea sativa Mill., Quercus robur L. and Acer pseudoplatanus L.) grown in monoculture and a two species mixture on soil hydraulic properties were examined using a combination of root morphological characteristics collected from three soil layers (0-0.1, 0.1-0.2, 0.2-0.3 m) and soil physical properties from two soil layers (0-0.05, 0.1-0.15 m) at BangorDiverse, north Wales, whilst the interaction of F. excelsior with soil types of contrasting soil textures was examined at four sites across England and Wales. Fine root biomass (FRB) was positively correlation with field-saturated hydraulic conductivity (Kfs) and altered soil macroporosity and hydraulic function. Fine roots of F. excelsior were found to alter soil hydrology independently of soil type in the top 0.1 m of soil, where the majority of FRB is found, but below this, soil type mediated hydraulic function. In the mixed species plots, hydraulic conductivity was not affected by species richness per se, but by species identity. Tree species with contrasting functional traits, namely B. pendula and C. sativa, benefitted from a mutualistic relationship and belowground overyielding that resulted in a significant increase in Kfs compared to C. sativa in monoculture. Where mixtures consisted of species with similar functional traits e.g. F. excelsior and B. pendula, no belowground overyielding and a significant reduction in F. excelsior FRB and macroporosity was observed. Woody hedgerows in pasture-livestock farming systems were then used to investigate seasonality and soil type interactions on soil hydraulic properties. Soil matric potential was measured every 30 minutes for a year up- and downslope of a hedgerow on seasonally-wet (SW) and free draining (FD) soil types, and soil water retention curves determined. Soil macroporosity was 14-25% of total pore space under hedgerows, compared with 2-4% in pasture and 9-14% next to a stone wall, and soil moisture was significantly lower adjacent to hedgerows for 10-months of the year. At the SW site the hedgerow created a disconnect in lateral and vertical subsurface flow, whereas at the FD site no break in hydrological connectivity was observed. This thesis has shown that: (i) Soil macroporosity is increased by the presence of trees and the magnitude of change is tree species specific; (ii) widespread loss of F. excelsior from disease could have a large impact on local soil hydrology; (iii) species selection based on contrasting belowground functional traits to maximise niche differentiation should be considered where hydrological regulation is a key objective; and (iv) hedgerows can interrupt hydrological flow paths, and reduce flood risk, but the magnitude of change will depend on underlying soil types. These results suggest that the incorporation of trees into the landscape as hedgerows and forests has potential to improve flood risk management and that land managers and modellers should consider the traits of individual species when planning afforestation.