DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 11-12/2020 str. 23 <-- 23 --> PDF|
Pažut. The forest of spreading elm and narrow-leaved ash Fraxino-Ulmetum laevis Slavnić 1952 inhabits the highest positions of floodplain areas along large rivers. The forest of grey alder Alnetum incanae Luedi 1921 is distributed along the entire course of river Drava (Vukelić et al. 2005.)
MATERIALS AND METHODS
MATERIJALI I METODE
Fieldwork was carried out from February to May during breeding seasons 2016, 2017, 2018 and 2019. For bird community sampling standard point count method was used (Bibby et al. 1992). The research was carried out on 66 counting points at least 300 m apart. All counting points were at least 300 m from the forest edges to avoid the edge effect. Every counting point was visited five times during the breeding season. To cover the period of highest bird activity, each visit started after the sunrise and ended three hours later. Singing males were considered as representing breeding territories. Non-singing birds were noted but excluded from the final analysis. Counting period was five minutes. Two counting bands were used: inner band with a diameter of 50 m from the observer and outer band outside the diameter of 50 m. Birds were recorded separately for inner and outer band. Only birds recorded in the inner bands were used for quantitative analysis. A digital voice recorder was used during the counting in order to improve the determination of species with similar songs (eg. tits).
Habitat sampling described here differs from standardised forestry methodology and therefore is not comparable with methods used in systematic forest inventory in Croatia. The sampling was carried out at each counting point using the circular plot method (Bibby et al. 1992, Cyr and Oelke 1976, James and Shugart 1970). Plot diameter was 11.28 m. For each tree inside the plot tree species and tree diameter (DBH) was recorded. Tree diameter was measured using a calibrated ruler and is given in nine classes: S < 7.5 cm, A 7.5 – 15 cm, B 15 – 23 cm, C 23 – 38 cm, D 38 – 53 cm, E 53 – 68 cm, F 68 – 84 cm, G 84 – 101 cm, H > 101 cm. In each diameter class basal area was calculated by multiplying the number in each class with factors provided by Cyr and Oelke (1976). To determine the relative stand maturity total basal area in a plot was divided by the number of trees. The data for stand age was obtained using Croatian forestry inventory and pooled into four age groups: <40 years, 40-60 years, 60-80 years and >80 years. Also, trees from groups S, A and B were pooled together as “small” and C to H as “large” trees. Additionally, the proportion of tree basal area per species was used to identify counting points with dominant poplar (Populus sp.), alder (Alnus glutinosa) and ash (Fraxinus angustifolia). Counting points with more than 60% of tree basal area belonging to each of the species were classified as poplar, alder or ash stands. Counting points