Ecological measurements within CTCD

        Caroline Nichol and John Grace.

        Within CTCD a range of measurements are being made of soil and vegetation ecosystem variables. Details of measurements of soil are on the soil science project page. This section describes ecosystem meaurements being made at CTCD test sites such as Harwood Forest, Northumberland by the Edinburgh team.

        Forest ecosystem measurements

        Edinburgh are providing carbon stocks, fluxes and structural data for five European forests, which occur as chronosequences and will be made available to other CTCD partners. Harwood forest, which is the core study site in the UK for CTCD is representative of much of the UK's afforestation over the last 30 years and will be studied intensively in 2003 when there will be over-flights, phenological observations and biochemical measurements

        The primary data source is the flux tower based at Harwood Faorest. The eddy covariance system on the tower (based around the open path) was set up in May 2003 ran continuously until November 2003 it was replaced with a closed path system. A subset of December's flux data is shown in Figure 1.

        Figure 1. Example of net CO2 exchange data from December 2003 for Harwood forest, Northumberland. Even in December there is significant photosynthesis. Harwood is a core site for ground truthing EO products.

        During 2003 we were to focus on tower-based hyperspectral measurements from the Harwood chronosequence, covering clear-fell sites and forests of different ages, and measurement of the photochemical reflectance index (PRI), with derivation of the relationship between PRI and light use efficiency (LUE). Due to weather problems we achieved only 3 sets of spectral measurements from the tower (from weekly trips to the field) and realised quickly that the focus had to shift to using spectral sensors that would log continuously under any illumination conditions. Since then, we have collaborated with the NERC Geophysical Equipment pool and colleagues in the Edinburgh Earth Observatory, as they have built a continuously logging narrow-waveband spectral sensor, which we tested on the tower in August. It has had several revisions and we hope to have it mounted on the tower soon to get the seasonal data we set out to collect last year.

        We carried out one set of helicopter flights, in collaboration with UCL, over the chronosequence at Harwood which was to be followed up during the growing season but bad weather hampered the achievement of this goal.

        We have also recently joined a working group called SpecNet (short for Spectral Network) which was set up by Professor John Gamon at California State University, and builds on existing capabilities of the flux tower network by adding spectral measurements to existing flux tower sites at a range of ecosystems around the world. The aim is to facilitate an understanding of factors controlling terrestrial carbon fluxes and providing key information for modelling and validating emerging satellite data products. We will further explore the possibilities of making the same measurements from satellites such as CHRIS-PROBA, taking into account the sensors which are flying now and those which will fly in the next five years. We will also evaluate the relationship between the LUE derived from these relationships and the LUE expected from the SPA model. These measurements form part of a developing collaboration with UCL on the development and testing of biochemical models, and their inversion.


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