Allometric Models of Biomass for Understory Trees and Shrubs in Pine Stands of Voronezh Oblast

Accurate estimation of biomass in the lower forest layers is required to refine assessments of biological productivity in forest ecosystems; however, species-specific allometric relationships for understory trees and shrubs in pine stands of the forest-steppe zone remain insufficiently studied. The aim of this study was to obtain empirical data on the structure of aboveground and belowground biomass of understory species in the Central Forest-Steppe and to assess the potential for predicting biomass from basal stem diameter and plant height. The study was conducted on permanent sample plots established in pine stands of the Levoberezhnoe District Forestry within Prigorodnoye Forestry, Voronezh Oblast, Russia. Understory characteristics were assessed using a sample plot network where species inventories were conducted, plant height and basal diameter were measured, and sample plants were selected for destructive analysis. The dataset comprised 75 sample plants representing seven species, for which leaf mass, aboveground biomass, and belowground biomass was determined by destructive sampling. Log-transformed allometric equations were developed for individual biomass components using basal diameter and plant height as predictors. Model performance varied among species, biomass components, and predictor variables, indicating pronounced species-specific patterns in the resulting allometric relationships. A clear species- and biomass-component-specific character of the allometric relationships was observed. The most robust relationships were obtained for red elderberry (Sambucus racemosa), for which the predictive ability coefficient (Q2CV) ranged from 0.532 to 0.863. Positive predictive ability was also found for models developed for red raspberry (Rubus idaeus), field maple (Acer campestre), and European spindle (Euonymus verrucosus). The strong relationship between belowground biomass of round-leaved serviceberry (Amelanchier ovalis) and basal stem diameter (R2adj = 0.929, Q2CV = 0.630) should be regarded as preliminary because of the small sample size (n < 10). For rowan (Sorbus aucuparia) and common hazel (Corylus avellana), neither basal diameter nor plant height provided robust univariate predictions of biomass. No single morphometric predictor was universally superior: basal stem diameter was more informative for certain biomass components of red raspberry and red elderberry, whereas plant height performed better for particular biomass components of field maple and European spindle.