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Regeneration of forest ecosystems is crucial for preserving their structure, function and long-term stability. This research analyses the correlation and similarity of the occurrence of 11 species characteristic only for the regeneration phase with respect to some soil properties. Aim of research is to perform grouping of species according to soil properties, and to determine differeces in clusters trough Ellenberg's (1974) indicator values. Soil properties were analysed based on the content of carbon and nutrients (Ntot, Ctotal, Corg, B, Ca, Cu, Fe, K, Mg, Mn, Na, P, Zn and pH-values (pHH2O, pHCaCl)) in the soil. Seven categories were used to classify the species' occurrence, 0: 0%, 1: (0,1)%, 2: 1-10)%, 3:10,25)%, 4:25,50)%,5:50,75)%,6: >=75%.
The research was done on 10 plots (20x20m) in the phases of regeneration (shelterwood cutting) of pedunculate oak forest in eastern part of Croatia (Spačva area).
Spearman rank correlation coefficients were obtained between soil chemistry variables and species occurrence. Based on these correlation coefficients, species were clustered. First, hierarchical clustering (Euclidean distance and Ward method) was used, where it was concluded that species were grouped into 2 main clusters, after we compare our results with the non-hierarchical k-means procedure assuming the number of clusters as the result of Ward method. Cluster 1 consists of the species Calamagrostis epigejos (L.) Roth, Epilobium angustifolium L. and Solidago gigantea Aiton. These species indicate open habitats, rich in nitrogen, mostly indifferent to temperature and moisture. With regard to soil reaction, these are indifferent species or indicators of heavily acidic soils.
Cluster 2 consists of 8 species (Urtica dioica L., Erigeron annuus (L.) Desf., Solanum dulcamara L., Quercus robur L., Acer tataricum L., Cirsium palustre (L.) Scop., Eupatorium cannabinum L., Lapsana communis L.) with lower indicator values for light than the species of Cluster 1, and according to Ellenberg somewhat higher values for moisture and soil reaction.
By decreasing the value of pHH20, pHCaCl, Ca, Mg, Mn, species from Cluster 1 have a higher representation, while Cluster 2 has a decreased representation of the species. For increased values of K, Cluster 1 has increased species representation, and Cluster 2 has decreased. An increase in C in the soil decreases the representation of species in Cluster 1, while it increases in Cluster 2. B, Fe and Zn do not show any significant relationships with species occurrence.
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