Renata Pernar

DEM-based depth in sink as an environmental estimator

The sink as a geomorphological feature can modify a spatial distribution of soil moisture due to the water stagnation in the flood-plain region or spatial distribution of air temperature and humidity (air confluence effect) as well as soil depth in the karstic region. A new variable based on digital terrain model, depth in sink, is introduced as an environmental estimator. The ability of the new variable to explain spatial distributions of the relative presence of dominant tree species is tested in the case study for a karstic region (Europaean Silver Fir, Common Beech, Norway Spruce and Mountain Pine) and for a flood-plain region (Pedunculate Oak and Narrow-leaved Ash), both in Croatia. The general linear modelling method was used. Depth in sink was the significant estimator of the spatial distribution for all tested tree species.

Epizootiological survey of small mammals as Leptospira spp. reservoirs in Eastern Croatia.

In this survey we investigated a population of small mammals in Eastern Croatia in order to determine Leptospira carriage rates and identify circulating serovars. Out of 67 trapped animals, 20 (29.9%) isolates were obtained. Identification of isolates using microscopic agglutination test, pulsed field gel electrophoresis and multi locus sequence typing revealed that 10 (50.0%) isolates belong to serogroup Pomona, serovar Mozdok, 6 (30.0%) isolates to serogroup Australis, serovar Jalna, 2 (10.0%) isolates to serogroup Sejroe, serovar Saxkoebing, and 1 (5.0%) isolate to serogroup Grippotyphosa, serovar Grippotyphosa. One isolate from serogroup Bataviae was unable to be identified to the serovar level. Amplification of a 331-bp region of the locus LA0322 using real-time polymerase chain reaction determined that 12 (60.0%) isolates belong to L. kirschneri, 6 (30.0%) isolates to L. interrogans, and 2 (10.0%) isolates to L. borgpetersenii. Leptospira carriage rate was high (29.9%), which corresponds to a high incidence of human and domestic animal leptospirosis in Eastern Croatia. Furthermore, 90.0% of the isolates belong to serogroups Pomona, Australis and Sejroe which are also the most prevalent serogroups in humans in this area. These findings suggest that small mammals might be an important source of Leptospira spp. infection in Eastern Croatia.

The incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) in Croatia

The research on incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) was carried out in natural fir stands in Croatia. In the area of Gorski Kotar 32.8 % of the examined dominant fir trees were infected with mistletoe. The mistletoe incidence was presented according to the damage degrees of silver fir from 0 (healthy trees) to 4 (dead trees), rated by the crown defoliation and needle discoloration. With the increase of incidence, mistletoe spreads more onto more vital, i.e. less damaged trees. In the Dinaric Alps 28.6% of the examined fir trees were infected, this percentage amounting to 27.1% for the mountainous regions between the Sava and Drava rivers.The site and stand parameters (exposure, elevation, site quality, forest community and crown closure) were analysed in order to establish whether there was a correlation between these parameters and mistletoe incidence. There was a negative correlation between the elevation and mistletoe incidence. Among the compartments with a closed stands there were considerably less compartments with higher mistletoe incidence than among compartments with a sparsely closed and understocked stands. The other analysed site and stand parameters individually had no significant influence on mistletoe incidence.The correlation of silver fir mortality in 2004 and mistletoe incidence in 2002/03 was analysed, and their strong correlation was established. Mistletoe could be considered as a bioindicator of silver fir decline, and probably a significant contributor to that decline. In the areas where mistletoe incidence is great it can be presumed that silver fir is significantly damaged.

Picture histogram and interpretation of digital orthophotos in forest management

The paper presents the possibilities of using histograms of a stand scene and visual interpretation of a digital orthophoto to estimate stand density and condition. Black-and-white aerial photographs with an approximate scale M /spl ap/ 1:20,000 and 60% overlap, obtained during cyclical survey of the Republic of Croatia, were used for this purpose. According to research results, there are three basic forms of histograms which may be associated with the corresponding density categories. They may also purposefully be used to estimate the density and condition of a stand. Furthermore, the form of histograms of stand scenes corresponds to stand descriptions. Stands with normal and poor density may be defined with digital value classes, while stands with density between 0.50 and 0.80 cannot be specified accurately. Ocular assessment of density based on stand canopy was also made, and firm correlation with concrete density was established, i.e. it was found that canopy may be used as a measure of density.