Tamàs MOLNAR, (institut de recherche forestière NAIK ERTI, Hongrie).

Ground-based forest observations in Hungary have recently been completed by a wall-to-wall system (in Hungarian: “TEMRE”) to monitor forest health in relation to environmental changes (including climate change). The system is based on free images with a 250*250 m (moderate) resolution from the MODIS sensor of the Terra OSM satellite. Once in every 16 days during the vegetation season (May-October), NDVI values are automatically downloaded for the entire country, masked for the Hungarian forest area, filtered for errors, and classified using standardized NDVI-index (Z) values. Forest maps showing the actual status of the forest cover by colour-coded values are then developed and published at klima.erti.hu/TEMRE.php. The discoloration of pixels in any forest with health issues can be due to, among others, lasting physiological deficiencies (caused by factors such as drought, heat stress, lack of nutrients and biotic agents) or abrupt leaf area loss (caused by pests, late frost, strong wind etc.).
The attribution of discolorations to specific causes, to be attempted for larger (>1000 ha) contiguous areas, is supported by information on the distribution of tree species (currently, the ten most common ones) and site conditions (currently using map layers of climate type, elevation, hydrological conditions, mean water table level, rooting depth, soil texture, aspect and slope). Site conditions determinate both where the various species and forest associations can be found and how trees grow but also how they may affect forest health. Determining separately and numerically the effect of the various site factors is impossible, however, analyzing the geographical overlapping of these conditions and forest health might help identify reasons of possible issues.
Development plans include the usage of new, higher resolution satellite images, new vegetation indices, and developing methods for reliable validation from field measurements. Sentinel-2 L2A images (10*10 m) of European Space Agency have already been used in specific areas to identify precisely the expansion of known forest calamities (abiotic: ice-break, wind-break, wind-fall or biotic agents). Different forest health state indicators (NDVI, LAI, and classified land cover maps) were also tested and validation was done by field data of the Hungarian National System for Identification and Registration of Forest Damages (in Hungarian, OENYR). It is also planned to exchange MODIS tiles to forest sub compartment polygons for better comparison. Studies are recently being conducted to investigate the results of these developments.

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Aide mise à jour Scopia, janvier 2016 (Client)