Vegetation cover and soil management practices affect the soil hydraulic characteristics which regulate water balance. Therefore, changes in land use can have large impacts on plant-water availability, groundwater recharge and (erosive) surface runoff. Such changes have a distinct effect on soil structure and thus modify the soil pore-size distribution, which makes saturated and near-saturated soil hydraulic properties particularly sensitive to them. These parameters can be estimated in the field and used to predict and simulate the hydrological impacts of changes in vegetation and/or management.

Some research has focused on the impact of vegetation cover and soil management changes on soil structure (e.g. Angers et al., 2004; Hildebrand, 1996; Hildebrand & Schack-Kirchner, 2002); parameters such as bulk density, macropososity and saturated/near-saturated hydraulic conductivity can be used as indicators of the soil's 'physical fertility' (e.g. Tebrügge and Düring, 1999; Blair et al., 2006; Ball et al., 2007). The incorporation of these results into models which quantify soil structure changes, and consequences for hydrological properties, is rarely done (Roger-Estrade et al., 2009). However, saturated and near-saturated soil water flow properties are very sensitive to the macro-pores generated by structure-building processes, including plant and management-induced processes This can be used as a basis to model the dynamical behaviour of soil hydraulic properties as affected by changes in land-use (e.g. Leij et al., 2002). With detailed information on the hydrological behaviour of soils under different vegetation cover conditions, this type of model can be adapted for specific areas and land covers, as demonstrated by Schwärzel et al. (2010). Examples of required information include laboratory measurements of soil hydraulic behaviour, field measurements of infiltration (e.g. Schwärzel and Punzel, 2007), or tracer experiments to visualise infiltration pathways (e.g. Flury and Flühler, 1995).

Forest soils in wet Mediterranean regions such as NW Portugal provide a challenging opportunity for this research. Land cover typically consists of commercial forestry; plantations with maritime pines having been progressively replaced by eucalypt, leading to changes in forest hydrology (e.g. Shakesby et al., 1996; Ferreira et al., 2008). The hydrological properties of these soils are complex, and show seasonal variability following the wet and dry seasons of Mediterranean climates; for example, forest soils often show severe soil water repellency (Doerr et al., 1996) with strong seasonal fluctuations (e.g. Keizer et al., 2005, 2008). The region is also prone to recurrent wildfires which lead to important changes in soil hydrological properties (Shakesby and Doerr, 2006). There is, however, little research into predicting these changes and their consequences for water balance.

This action focuses on the impact of different forest plantations - eucalypt and maritime pine - for soil hydraulic characteristics in Portuguese forests. Given the economic importance of forestry, the water requirements of tree species and the frequent occurrence of mild and severe drought years, knowing the behaviour of soil hydrological properties is an important area of research for the sustainable management of forest stands. The work should serve as a "kick-off" for long-term cooperation between the German and Portuguese partners on forest soil water research. The fundamental research to be conducted during this action should provide a basis for:

• Quantifying the impact of vegetation cover changes, related with different forest management practices (notably in eucalypt and maritime pine plantations), in soil structure and hydraulic characteristics;


• Building a numerical description of these changes which can be implemented in hydrological models.

CESAM members on this project

Diana Catarina Simões Vieira
Researcher

Researcher