Species composition and aboveground biomass of shrubs in the understory of the Niepolomice Forest

The understory, a layer composed predominantly of shrubs that perform an important phytomeliorative function, has rarely been the subject of research on the productivity and biomass. The aim of this paper was to specify the occurrence of understory aged >= 10 years as well as its species composition and the share of individual species in the biomass in the Niepolomice Forest (S Poland). The analysed features were related to the age and site conditions of the stands. The research material consisted of dry biomass of shrubs growing within circular sample plots spaced 500 m apart from each other. Dead and live (damaged and undamaged) shrubs of dbh<7 cm were cut at a ground level to determine their wet mass and samples were taken to determine the dry mass. The mass of live shrubs was calculated based on empirical formulas. 368 sample plots were set up in total. Shrubs (13 species) were observed on 76.1% of plots. Shrubs were the most common in the stands of II and IV age groups (87% of plots). No shrubs were observed on the plots with stands older than 160 years. The most common species was Frangula alnus (56.8% of the plots). Quite common ones included Sorbus aucuparia (27.7%) and Padus avium (12.8%). Cornus sanguinea, Prunus spinosa, Salix cap rea and Viburnum opulus were observed on less than 1% of the sample plots. Frangula alnus and Padus avium were inventoried in as many as 8 forest site types. The largest amount of shrubs (10 species) were observed in moist broadleaved forest stands, while the fewest (2 species) in boggy mixed broadleaved and ash-alder swamp stands. Over 56% of the aboveground biomass were live shrubs of dbh <7 cm (868.6 kg/ha), almost 29% (444.1 kg/ha) were shrubs of the dbh >= 7 cm, and around 15% (227.6 kg/ha) of the biomass were dead shrubs. The total aboveground biomass of shrubs in the understory of the analysed stands equaled, on average, to 1,540 kg/ha. 94% of the biomass was the aboveground woody biomass including bark (1,448 kg/ha). The dry mass of leaves amounted to 92 kg/ha (6%). Due to high variability of the understory biomass, the estimation error of its average amount was almost 11.4% for total biomass and 13.5% for leaves.