Dipl.-Geogr. Markus Tum D-82234 OberpfaffenhofenGerman Aerospace Center (DLR) GermanyGerman Remote Sensing Data Center (DFD) Tel. +49 8153 28-1572Land Surface Dynamics Fax +49 8153 28-1458

E-Mail markus.tum@dlr.de

Derivation of Energy Resources from Modelled Net Primary Productivity for Germanys Forests

M. Tum, M. Niklaus, K.P. Günther

German Aerospace Center (DLR), German Remote Sensing Data Center (DFD), Land Surface Dynamics

We present an approach to derive theoretical energy potentials of German forests from modelled NPP. Germany was chosen as area of investigation. Our NPP results are computed with the vegetation model BETHY/DLR (Biosphere Energy Transfer Hydrology Model). BETHY/DLR is a modification of the JSBACH model which computes the biosphere-atmosphere exchange within the ECHAM5 global climate model. Primarily the photosynthetic rate of vegetation types is computed with time steps of one hour and with 1km² resolution. It includes modules for assessing the water balance and the radiative energy transfer between atmosphere, vegetation and soil. The model is driven by remote sensing data sets including land cover / land use from GLC2000 and time series of Leaf Area Index (LAI), derived from SPOT-VEGETATION. In addition meteorological parameters provided by the European Center for Medium Range Weather Forecast (ECMWF) and soil type information by the Food and Agriculture Organisation are used.

Fig 2: Sustainable theoretically available energy potential, in terajoules per 1 km² pixel, of forest areas in Germany for 2000 and 2001. Low energy potentials are shown in blue, intermediate potentials in beige, and high energy potentials in red. White represents areas which are not designated as forested by GLC2000

Fig 1: Estimated above-ground biomass from modelled NPP versus empirical data from the NFI for Germany’s deciduous and coniferous trees for 2000 and 2001. Each cross represents one NUTS-1 region. Thick lines show linear regressions. Values are given in megatons per NUTS-1 unit per year.

The modelled NPP integrated over one year represents the increase of total biomass. For the validation we used data about the increase of above ground biomass (AGB), derived from the National Forest Inventory (NFI) of Germany for 2000 and 2001. The NFI contains information for the four main tree species in Germany (beech, oak, pine and spruce) on NUTS-1 level, given in steps of twenty years (0-20, 20-40, …).

The validation is performed by converting modelled NPP to AGB at NUTS-1 level. This is done by applying volume expansion factors. With this method high coefficients of determination (R²) of up to 0.95 are found (fig 1). These are combined with slight overestimations (deciduous trees) and underestimations of around 30% (coniferous trees). The result shows that the presented method delivers highly correlated results and can be seen as suitable for validating modelled NPP with statistical derived data.

In a second step theoretical energy potentials were substituted from the modelled and validated NPP results, assuming sustainable management of forests, meaning only the annual increase of AGB is used for energy production. This is done by using tree species and age depending heating values. Applying this, theoretical energy potentials of up to 695PJ are found (fig 2).