Spanjol Z.,University of Zagreb |
Rosavec R.,University of Zagreb |
Barcic D.,University of Zagreb |
Galic I.,Rudarsko geolosko naftni fakultet
Croatian Journal of Forest Engineering | Year: 2011
In terms of its biodiversity, the Mediterranean area is one of the most important regions in the world. In recent years this area has often been affected by forest fires. Forest fires are the most important and most powerful environmental factor causing changes (Trabaud 1991, Casal 1985, 1993 Calvo, Le Houerou 1993, Pyne et al. 1996, Naveh, 1999). When talking about the occurrence and spread of forest fires, vegetation characteristics, fuel supplies and climate factors (mean atmospheric conditions) are the most decisive and important factors of natural origin (Rosavec 2010). Fuel is any substance or mixture of substances that can be ignited and burn. Forest fuels mostly come from pine culture, especially when speaking of younger stands. As we cannot have a direct impact on climate, geology, soil and relief factors, our efforts should be focused on potential availability of forest fuels and vegetation where we can prevent the occurrence and spread of wildfires. Accordingly, and with favorable climatic conditions for starting forest fire, fire risk can be reduced to a minimum if care measures are taken regulating the amount of the potential of forest fuels. Therefore, timely and according to professional standards of care measures derived stands and culture greatly influenced the reduction in the number and size of fire burn area. Testing of ignition delay, i.e. the time required to ignite the sample, and burning duration, or time elapsed from the moment of ignition to self-quenching of the sample, and determination of moisture content of dead (discarded needles) and living (green needles) fuel was carried out in the period from June 2007 to June 2009 at the educational center NP[O Rab, Faculty of Forestry, University of Zagreb, in a 40-year stand of Aleppo pine (Pinus halepensis Mill.). The methodology prescribed by Valette (1990) was used to test the ignition delay and burning of the living fuel. The moisture content of tested samples of living and dead fuels were obtained using a standard equation for determining the moisture content (percentage of dry weight), the drying method. Investigations were conducted on the island. It is located in the Kvarner group of islands, and along with several surrounding islands, islets and reefs makes the Rab archipelago. In the structure of the Island of Rab, Upper Paleogene Quaternary sediments are present but they are much less developed, while chalk and Paleogene sediments largely prevail. Walter climate diagram (Walter 1955) was used to view the annual variation of air temperature and precipitation was used. He, among other things, shows the relationship mean monthly temperature and precipitation (Fig. 2). The frequency of certain wind directions is shown in the wind rose (Fig. 3). According to Trinajsti} (1986), the forest vegetation of the Island of Rab belongs to the Mediterranean region, i.e. to the Mediterranean-littoral vegetation zone and eumediterranean vegetation zone of evergreen forests. The results of multivariate regression analysis of ignition delay of Aleppo pine (Pinus halepensis Mill.) on Rab are shown in Table 1. There was no statistically significant dependence of the ignition de-lay on used variables of climate factors. Table 2 presents the results of multivariate regression analysis of the duration of combustion of Aleppo pine (Pinus halepensis Mill.) on Rab. They show no statistically significant dependence of the DC on used variables. Table 3 presents the results of multivariate regression analysis of moisture content of green needles of Aleppo pine (Pinus halepensis Mill.) on Rab. They show no statistically significant dependence of their moisture content and climatic variables used. Table 4 presents the results of multivariate regression analysis of moisture content of discarded needles of Aleppo pine (Pinus halepensis Mill.) on the Island of Rab. There is a statistically significant dependence of moisture content of discarded needles on all variables. The results of research show that the main climatic parameters have no significant influence on the ignition delay, combustion duration and moisture content of green needles, as opposed to discarded needles where the impact is statistically highly significant. This clearly indicates the importance of conducting forest silvicultural and tending activities aimed at timely and properly reducing the amount of dead fuel, or discarded needles, as a potential source for the occurrence and further development of the fire.
Jaguljnjak-Lazarevic A.,Rudarsko Geolosko Naftni Fakultet |
Dvornik J.,University of Zagreb |
Frgic L.,Rudarsko Geolosko Naftni Fakultet
Gradjevinar | Year: 2011
In order to estimate accuracy of structural analyses, the authors introduce a systemic set of examples with analytic solutions that can be presented, through the finite element method, in form of whole numbers and fractions. The three-cube Lagrange element in form of cuboid is selected as an example. Examples are solved numerically using a standard number of significant digits. In the end, an accurate calculation of error is derived from the difference between the exact and numerical solutions. The entire procedure is realized using the Mathematica software.
Duic Z.,Rudarsko geoloSko naftni Fakultet |
Briski M.,Hrvatski GeoloSki Institute
Rudarsko Geolosko Naftni Zbornik | Year: 2010
Shifts of structural units, which started in Pliocene are specifically expressed during the Quaternary. They last still today and affected the hydrogeological relations in the region of Baranja. Lithological development is dominated by one or maximum two layers of uniform midium grained sand which in places exceeds to fine grained sand, and in some places in the sand with gravel. Mentioned structures have impacted the natural quality of groundwater. Considering individual episodes of uplift and lowering of sediments, caused by movements along a particular structures, led to changes in oxidative and reductive conditions of deposition. Consequently, different quality of water occurs in wellfields of Baranja.