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A strategic programme for NERC Lowland catchment research
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Influence of woodland on recharge: summary

A fuller description of this project is also available.

Overview of project

Comparative measurements of recharge rates under woodlands and grasslands in southern England have produced inconclusive results so far. This has caused a controversial debate about the actual evaporative water loss from woodlands and the impact of afforestation and deforestation on the catchment water balance. The few reliable data for evaporation come mostly from extensive, homogeneous woodlands, which are suitable for micrometeorological evaporation measurements. However, such woodlands are not representative of the English lowlands.

Field instrumentation

In order to assess the impact of woodlands on the catchment water balance the LOCAR woodlands project investigated evapotranspiration rates for various woodland types that are more typical for the region and which have been overlooked in previous research. The key technique used to measure woodland transpiration was the sap-flux method, which is applied at the tree-scale and is therefore suitable for any kind of woodland. Complementary measurements of the rainfall interception loss, as an additional component of woodland evaporation, were also made at some of the sites.

Aims

Primary aims of this project were to:

  • measure evaporation from major components of the woody vegetation in a lowland catchment;
  • derive descriptive models of woodland evaporation; and
  • estimate the impact of woodland vegetation, and changes in it, on catchment recharge.  More about the aims of this project

Main findings

Description of activities

Field work

  • The transpiration of the woody vegetation at six sites in and near the Pang catchment was measured by the sap-flux technique.
  • The tree canopies investigated were hedgerows, woodland edges, heterogeneous woodlands and wet woodlands.
  • The rainfall interception evaporation was measured at three sites.
  • All sites were equipped with automatic weather stations.
  • Surveys of tree species and stem diameters at each site.  More about the activities carried out by this project

Laboratory and analytical work

  • A re-calibration of the sap-flux technique in the laboratory.
  • The canopy transpiration was compared to the potential evaporation and used to derive the stomatal conductance through the Penman-Monteith equation.
  • Seasonal water use and the stomatal behaviour for these types of woodlands were quantified for the first time.
  • Rainfall interception was calculated as the difference between gross rainfall and throughfall plus stemflow.
  • The Gash model of rainfall interception was parameterised for the hedgerow site and the oak dominated woodland.  More about the activities carried out by this project

Areas of application

  • Modelling the water use of forested areas
  • Predicting the impact of afforestation or deforestation on the catchment water balance
  • Managing water resources in a changing climate.

Related work

So far the publications from the project refer to the findings from specific sites. It is intended to integrate those papers in such a way as to compare the water use and the stomatal behaviour across all sites investigated in the project and to quantify the impact of changes in the area and the type of woodlands on the water balance of the catchment.

Researchers' details

Principal Investigator:

Co-investigators:

Publications

All publications from this and other LOCAR projects are listed in the publications database.

Selected publications from this project are listed below. The full list of publications and recommended reading can be viewed in the full description page for this project Full publication list for this project

Selected publications

Herbst M., Roberts J.M., Rosier P.T.W. & Gowing D.J. (2006) Measuring and modelling the rainfall interception loss by hedgerows in southern England. Agricultural and Forest Meteorology 141, 244-256.

Herbst M., Roberts J.M., Rosier P.T.W. & Gowing D.J. (2007) Seasonal and interannual variability of canopy transpiration of a hedgerow in southern England. Tree Physiology 27, 321-333.

Herbst M., Roberts J.M., Rosier P.T.W., Taylor M.E. & Gowing D.J. (2007) Edge effects and forest water use: A field study in a mixed deciduous woodland. Forest Ecology and Management 250, 176-186.

Full list of publications resulting from this project Full publication list for this project

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