DIGITALNA ARHIVA ŠUMARSKOG LISTA
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Secondary hole-nesters community / Zajednice sekundarnih dupljašica
In total, eight secondary hole-nesting species were recorded during the study (Figure 2): Marsh Tit (Poecile palustris), Eurasian Blue Tit (Cyanistes caeruleus), Great Tit (Parus major), Short-toed Treecreeper (Certhia brachydactyla), Eurasian Treecreeper (Certhia familiaris), Eurasian Nuthatch (Sitta europaea), Common Starling (Sturnus vulgaris), Collared Flycatcher (Ficedula albicollis). On average 3.02 pairs were recorded on each counting point. Most common species recorded was the Great Tit (35.18%). Shannon-Wiener index of diversity was highest in stands with dominant ash and was also increasing with stand maturity (Figure 3).
Habitat structure/Struktura staništa
In total, 14 tree species were recorded: common alder (Alnus glutinosa), narrow-leaved ash (Fraxinus angustifolia), commnon hornbeam (Carpinus betulus), field maple (Acer campestre), white willow (Salix alba), white poplar (Populus alba), black poplar (Populus nigra), pedunculate oak (Quercus robur), white elm (Ulmus laevis), field elm (Ulmus minor), black locust (Robinia pseudoacacia), bird cherry (Prunus padus), wild cherry (Prunus avium) common beech (Fagus sylvatica). The nine most common species were included in the analysis, with merged data for black and white poplar as well as on white and filed elm (Table 1, habitat variables). The average forest age was 59.8 ± 20.5 years, with ash and mixed stands being in average older than alder and poplar stands (Figure 4).
PCA analysis resulted with three principal components which accounted for 53.8% of the total variance (Table 1). PC1 accounted for 22.0% of the variance and was positively correlated with ratio of large trees and average tree basal area and negatively with total number of trees, ratio of small trees and number of small trees; and described the forest age. PC2 was negatively correlated with relative poplar number and basal area while PC3 was negatively correlated with relative alder number and basal area.
A significant positive correlation was found between number of bird species as well as number of pairs and all three axes showing preference to older stands and lower relative number of poplar and alder.
Riverine forests near Drava appear in narrow stripes along the river in the otherwise open agricultural landscape and represent a dynamic and ever-changing system. Some studies show the importance of riverine forests discovering high density and diversity of breeding birds in, or along, these forest stripes (Tworek 2002, Hågvar and Bækken 2005). Also, Rem et al. (2006) argued that riverine areas may be important centres of cavity supply in forested regions because old live trees with natural cavities provide a long-term and preferred nest-supply for hole-nesting passerines.
Structure of the secondary hole-nester communities recorded in this study are consistent with the research done so far in deciduous and mixed forests (Diaz 2005, Kirin et al. 2011, Kralj 2000, Sakhvon 2009). As was expected Great Tit is by far the most abundant secondary hole-nester.