Productivity of modal forest stands in Ukrainian Polissia depending on the compliance of the main tree species with the native forest type

The study aimed to assess the composition and mensurational characteristics of near-native and secondary forest stands, compare their mean annual increment with native references, and clarify natural productivity patterns across site conditions. The analysis was based on forest inventory data combined with geoinformation resources. Productivity was assessed by comparing mean increment values and ranking natural productivity scores. The average species composition of compositionally near-native modal stands differed from that of the reference native stands across most forestsite types. In poor and fairly poor site conditions, a higher share of silver birch (Betula pendula Roth) was observed; in fairly rich site conditions, higher proportions of birch (B. pendula) and European hornbeam (Carpinus betulus L.); and in rich site conditions, a suite of native hard- and soft-broadleaved species. Secondary stands showed the following patterns: in poor site conditions they were dominated by jack pine (Pinus banksiana Lamb.) and birch (B. pendula); in fairly poor and fairly rich site conditions by birch (B. pendula); and in rich site conditions by hornbeam (C. betulus), northern red oak (Quercus rubra L.), Scots pine (Pinus sylvestris L.), black alder (Alnus glutinosa (L.) Gaertn.), and birch (B. pendula). The mean increment of modal Scots pine stands exceeded native references by 17-58% in poor site conditions and by 2-48% in fairly poor site conditions, depending on the soil moisture regime, whereas in fairly rich site conditions, modal stands close in composition to native forests fell short by 19-37%, while in rich site conditions the increments were similar. In the most widespread site types in poor, fairly poor, and fairly rich site conditions, modal native stands were more productive than secondary ones; in rich site conditions, however, secondary stands prevailed by 13-16%. The productivity scores of modal stands differed substantially from those of the native reference scales: they were higher in poor and fairly poor site conditions but lower in rich site conditions. The highest natural productivity scores of secondary stands were recorded in fresh and moist rich site conditions and in fresh fairly poor site conditions. The obtained results provided a scientific basis for refining the scales of natural productivity and for typology-based planning of silvicultural measures