Summary
Automated stem-flow collector at Thetford Scots pine site
The ability of a forest canopy to intercept precipitation and the consequent reduction and spatial redistribution of water input to the soil play an important role in many hydrological, biogeochemical and ecological processes. An accurate description of the process of canopy rainfall interception is therefore critical not only for the estimation of the hydrological balance of forested areas but also for the performance of any high-resolution process model of forest growth and dynamics.
Research objectives
The aim of this project was to conduct a detailed study of the rainfall interception process and evaluate the applicability of one of the most widely used models of canopy interception, Gash’s model, at the short time scale usually required by current ecosystem process models.
Funders and partners
This project benefited from EU Forest Focus ‘C’ project funding.
Method
In order to parameterise and test Gash’s model, detailed data on precipitation components, meteorological conditions and canopy characteristics were collected over the year 2006/2007. Two sites were selected for this investigation:
- Oak site in southeast England (Alice Holt/ Straits Level II plot)
- Scots pine site in East Anglia (Thetford/ East Harling Level II plot).
Both sites are part of the network of long-term forest monitoring sites (UK Level II Programme, European Commission and ICP Forests of UN/ECE, 1996), but additional instrumentation was installed specifically for this project.
In particular:
- An array of 36 rain gauges per site was installed to allow monitoring of different precipitation components at half-hourly intervals: 6 gauges collected precipitation (both above the canopy and in clear areas outside the experimental plot), 20 collected throughfall and 10 collected stemflow.
- Two automatic meteorological weather stations per site collected half-hourly meteorological data both above the canopy and at ground level (below the canopy).
- Wind characteristics and profile within the canopy were also measured half-hourly by using sonic anemometers and a vertical array of high-precision cup anemometers mounted on pre-existing meteorological masts.
The seasonal canopy evolution was characterised through periodic surveys of hemispherical photographs from which canopy cover and leaf area index, corrected for clumping and woody components, were estimated.
Example of hemispherical photographs for Oak (left) and Scots pine (right)
Samples of foliage, branches and trunks were also collected at both sites to measure specific water holding capacity of foliage and bark using a soakage technique.
Storage and access to the collected experimental data was organized through the construction of an ad hoc database. From analysis of the measurements collected the rainfall interception capabilities and characteristics of the two stands could be determined.
Results
The measurement methodology employed in this study proved to be successful for a detailed characterisation of the canopy and for model parameterisation and evaluation.
It also set an example of the type of temporal and spatial resolution that is required in collecting measurements to support development, parameterisation and testing of process based models of ecosystem functioning.
Contacts
For details about the modelling component
Catia Arcangeli
Forest Research
Alice Holt Lodge
Farnham
Surrey GU10 4LH
Tel: +44 (0)1420 22255
Email: catia.arcangeli@forestry.gsi.gov.uk
For details of the instrumentation
Matthew Wilkinson
Forest Research
Alice Holt Lodge
Farnham
Surrey GU10 4LH
Tel: +44 (0)1420 22255
Email: matthew.wilkinson@forestry.gsi.gov.uk
