DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 13/2005 str. 79 <-- 79 --> PDF |
S. Husnjak. N. Pernar, R. Pernar, 1. Kisić: RISK OF WATER-INDUCED SOIL EROSION IN THE FOREST ... Šumarski list - SUPLEMENT (2005). 69-77 RESULTS AND DISCUSSION The potential risks of soil erosion is defined as the basic susceptibility of the soil to water-induced erosion in a given constellation of pedogenic factors, regardless of the vegetation cover and land use. The potential risk is the worst possible case, where the estimate of the potential risk of water-induced erosion is based on the assumption that the whole research area has no vegetation cover. Under such presumption, the crucial factors are soil erodibility, precipitation erosiveness, and terrain inclination. By overlapping the thematic maps of these factors within the space of forest ecosystems (Figure 1), we developed a map the areas of which were indexed in relation to the potential risks of erosion processes (Figure 2). This research revealed that under such presumptions 44.8 % of forest ecosystems in Croatia would be exposed to high potential risks of erosion, while 26.5 % of the area would be exposed to moderate risks (Table 1). The lowland areas and those with mild inclinations belong to the low risk class. Even on such areas, where there is no vegetation, some erosion processes take place, primarily as torrential or splash erosion caused by the effect of "bombing" or "shattering" the soil by raindrops. Such processes are slow and difficult to recognise. Over the slopes with higher inclination than 3 %, where the soil is "naked", sheet erosion takes place. The total forest area with high and moderate erosion risk amounts to 1,677,070 ha, or 71.3 %, indicating a high potential threat of water-induced soil erosion and the great significance of stable forest ecosystems for sustainable management, particularly related to agriculture and water management. Considering that soil is a conditionally renewable nature´s asset, and also a significant natural resource, any exploitation of forests aimed at their reduction leads to intensified runoffs and potential erosion processes. Today we witness massive encroachments on the forest, either by opening the corridors for roads, oil/gas/electric lines, or the mineral raw material mines. The supervision of the design, construction and manangement of such developments should be carried out by applying high security factors, because erosion processes occur to various extents, intensities and degrees of recognition. Soil protection is an imperative with any modern project made for terrestrial ecosystems. We should bear in mind what Gračanin said: "Croatian soils are the greatest national riches. To know them means to understand the foundations on which Croatia lies". The land use and the responsibility of land management are most drastically illustrated by the Mediterranean region (K o s m a s etal. 2002), with the forest fires the high frequency of which corresponds with irresponsible management methods (neglected areas with dominant weed vegetation and unorganised watch-information service) and inadequate ways of land use. The frequent fires are the objects of some methodological issues related to this research. The factor of the most destructive erosion processes on the Mediterranean forest areas, fire should be included into the model of estimating the real erosion risk. In addition, sustainable management should be supported by developing a map of potential erosion risks, based on updated and high-resolution data on the ways of land use and land cover. The map of land cover should include the attributes of the CORINE Land Cover programme. On the other hand, the application of the model to the Mediterranean and sub-Mediterranean areas presumes the assessment of both potential and real risks of erosion. CONCLUSION Croatian forest ecosystems arc mainly limited to the areas of moderate to high degrees of erodibility according to soil properties and relief/climate characteristics. The research has shown that 71 % of the forest ecosystem area is exposed to moderate and potentially high erosion risk. This requires more careful valorisation of forest ecosystems as priceless natural assets, indispensable for sustainable management of the whole Croatian territory, and the application of this model at regional level. Considering that the 90 % of the karst area is under potential erosion risk, this region should be regarded as a priority in the process of developing the updated high-resolution data on the land cover. The Mediterranean and sub-Mediterranean regions should be treated in relation to forest fires and their estimated characteristics. |