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V. Topic, I.. Bulorac: THE IMPACT OF SCRUB VEGETATION OF ORIENTAL HORNBEAM Šumarski list SUPLEMENT (2005). 40-50 ficult, its protection is of primary importance. In view of the above, scientific research dealing with karst soil erosion and protection was launched by the Adriatic Culture and Karst Amelioration Institute in Split in 1964. The first sample plots with measuring instruments were established in torrential watersheds of the Mediterranean karst area in 1971. The objective was to obtain original data on the key features of water-induced soil erosion using modern stationary methods. The plots, established at different inclinations and in varied geological and pedological characteristics, contain di verse plant cover. The results of past research have been published in several papers (Jcdlowski et al. 1975; Topic 1987, 1988; Topic and Kadović 1991; Topic 1995, 1996, 2001, 2003) and others. The paper deals with the results of research into the effects of oriental hornbeam scrub vegetation on soil protection against erosion. This type of vegetation covers the largest areas in the sub-Mediterranean karst of Croatia. Together with pubescent oak, they account for over 350,000 hectares and provide an important ecological stronghold. RESEARCH AREA AND METHOD OF WORK Research was conducted in the scrub vegetation of oriental hornbeam in sample plots B6 and B7 established on the slopes of Mount Moseć near Muć. The plots, situated at an altitude of 550 m, have a northern exposition and an inclination of 26°. They are built of cretaceous limestones with shallow to medium deep and very skeletal brown soil characteristic of the A-(B)rz- R profile (Vrbek, 1999). The plant coverage in the plots ranges from 61.14 % (plot B6) to 65.34 % (plot B7). The mean height of oriental hornbeam is 1.59 m and 1.79 m respectively. The cover has all the properties of a mixed forest of pubescent oak and oriental hornbeam (Querco-Carpinetum orientalis H-ić 1939), the most important forest community in the sub- Mediterranean karst region of Croatia. Even after several centuries of severe degradation, this community that grows on a shallow stone substrate covers very large areas (Figure 1). Seletković and Katušić (1992) classify the area of Muć into the Cfsax" climate type, which is characterized by a sum of annual precipitation of about 1,300 mm and a mean annual air temperature of 13.1 °C. This is temperate rainy climate with hot summers and a mean monthly air temperature above 22 °C. The winter rainy period is widely divided into spring (April to June) and autumn-winter maximum (October, November), with the driest part of the year occurring in the warm season. In order to obtain accurate assessments of the effects of oriental hornbeam scrub on soil protection against erosion, the scrub in sample plot B„ was cut down in 2001, while that in plot B7 was preserved (Figure 2). The plots were pedotaxonomically identified, the soil samples were taken from the pedological profile for laboratory analysis and the structure of the pedological cover was recorded. Samples of the leaf litter were collected from below the young trees of oriental hornbeam in an area of 0.09 m (Figure 3). Measurements of the vegetation cover in the sample plots included scrub height and horizontal crown projection, the example of which is given in Figure 1. Horizontal crown projections of all oriental hornbeam trees were recorded and entered in millimeter paper, which enabled planimetric determination of soil coverage with the crowns of each individual tree. The field ground plan of crown projections on millimeter paper was then scanned into a digital form using the Auto Cad programme. During the determined period, the erosive action of precipitation water was monitored and directly measured in the established sample plots. Investigation was made of the effects of the preserved oriental hornbeam scrub (plot B7) and the cut oriental hornbeam scrub (plot B6) on soil protection against erosion. The plots were encircled with concrete walls in order to prevent the inflow of lateral water and its uncontrolled outflow from the area. There are containers for collecting erosive detritus in the lower part of the plots. The person in charge of monitoring collected the data from the measuring instruments placed in the sample plots (rainfall gauge, ombrograph, thermograph, thermometer) every day at 7 o´clock a.m. and entered them in the meteorological station Monitor Log. In erosion days, he measured the quantity of water in the collectors and took samples for laboratory analysis. RESEARCH RESULTS Soil and elements of soil cover structure in sample plots The structure of the soil cover in sample plots B6 rocks that emerge to the surface in the form of smaller and B7 is characterized by shallow brown soil on listone blocks. mestone (calcocambisol) occurring among limestone |