Shrub height and crown projection area are effective predictors in aboveground biomass models for multi-stemmed European hazel

While numerous allometric models exist for estimating biomass in trees with single stems, models for multi-stemmed species are scarce. This study presents models for predicting aboveground biomass (AGB) in European hazel (Corylus avellana L.), growing in multi-stemmed shrub form. We measured the size and harvested the biomass of 30 European hazel shrubs, drying and weighing their woody parts and leaves separately. AGB (dry mass) and leaf area models were established using a range of predictors, such as the upper height of the shrub, number of shoots per shrub, canopy projection area, stem base diameter of the thickest stem, and the sum of cross-sectional areas of all stems at the stem base. The latter was the best predictor of AGB, but the most practically useful variables, defined as relatively easy to measure by terrestrial or aerial approaches, were the upper height of the shrub and the canopy projection area. The leaf biomass to AGB ratio decreased with the shrub's height. Specific leaf area of shaded leaves increases with shrub height, but that of leaves at the top of the canopy does not change significantly. Given that the upper shrub height and crown projection of European hazel can be estimated using remote sensing approaches, especially UAV and LIDAR, these two variables appear the most promising for effective measurement of AGB in hazel.