The Impact of Technical and Biological Measures on Soil and Erosion Dynamics in the Research Site of Abrami

摘要

Soil erosion is one of the most devastating soil degradation processes. In temperate climate regions, soil erosion rarely assumes excessive proportions. In the management of forest soil, the potential erosion threat drastically increases with an increase in climate aridity. Water erosion is particularly favored by parent materials of low water permeability and by soils derived from such materials. In theMediterranean and sub-Mediterranean area of Croatia, these are primarily flysch, marl and Werfen schists. These materials show good physical weathering properties, thus providing a rich source of erosion material.As a rule, the soil formed from such parentmaterial is of silty-clayey to clayey texture, and has a relatively low infiltration capacity. The soil unprotected by vegetation (burned sites) manifests particularly devastating forms of water-induced erosion. In the past 50 years, flysch terrains of Istria have been subjected to a series of technical, biological and biological- technical treatments aimed at preventing water erosion and recovering the eroded soils. An experimental (research) site was set up in Abrami near Buzet for the purpose of monitoring erosion processes and rehabilitation effects of different biological-technical and biological methods of eroded area recovery. The effects of the treatments on soil properties in the research site are in the form of progressive pedogenetic processes. Asynergy of the effects of recovery methods and different natural conditions (relief, vegetation) in the experimental site is particularly well reflected in erosion indicators, such as the production of erosion sediment (erosion production), and to a lesser extent, the surface flow index. For this reason, research in this work focuses primarily on soil properties and erosion production dynamics. From the geological-lithological aspect, the research site of Abrami is made up of Eocene flysch composed of alternate layers of light grey marl and dark lime sandstone, i.e. thinner or thicker interbeds of sandy limestone. The climate is sub-Mediterranean. The mean annual temperature is 12 °C and the mean annual precipitation is 975 mm. The natural potential vegetation in the localities is represented by the community of hop hornbeam and autumn moor grass. Established in 1956 on the slope exposed to highly pronounced erosion processes, the research site has an area of 23.46 ha.Aseries of technical and biological erosion recovery measures had been undertaken in the site by 1963 for the purpose of investigating their applicability in practice. Technical activities included the construction of step-like terraces, of the bench terrace type (?gradoni?), and contour rustic walls. Avariety of plant material was planted and seeds of different plant species were sown in the area (Table 1). Several control plots were also established in parts of the Abrami site, where either no treatment was applied or the seedlings were planted into the planting holes. Six plots intended for the measurement of erosion sediment production were established in 1969, followed by research into the quantitative erosion indicators, which started in 1970 (Table 1). After an interruption in 1977, measurements were resumed in 1997 and 1998 (two plots) and in 1999 (three plots). Erosion indicators have continuously been measured since 2000; however, measurements in plot I (plot I was omitted from this research due to its specific features) have been performed by means of terrestrial photogrammetry. The seventh plot was established in 2004, and has been the subject of measurements since 2005. This work encompasses measurement data from 2005, 2006 and 2007. The research includes plots II, III, IV,V, aswell asVI and VII. The soil and organic residues were sampled in the immediate surroundings of the erosion-measuring plots. Next to the plots in which no technical recovery measures were undertaken, a pedological profile was opened and the soil was sampled by horizons. Some