Carbon Storage by Siberian Larch in the Upper Treeline Ecotone in the Polar Urals

In the upper treeline ecotone the relationships between the values of biometric parameters of Siberian larch (average radius of the horizontal projection of the crown, the diameter of the tree at the root collar and its height) were studied using ground-based measurements on circular sample plots and ultra-high spatial resolution aerial photographs obtained by an unmanned aerial vehicle. A nonlinear regression model, a model using the random forest method and an ensemble of models using machine learning methods were created, establishing the relationship between the values of the diameter at the root collar and the crown radius of a specimen of Siberian larch. The resulting models have a high level of adequacy at the qualitative and quantitative (R²> 0.95) levels. The predictive capabilities of the nonlinear regression model outside the training set were better than those of the machine learning models, so it was used together with allometric equations to quantify the phytomass of Siberian larch based on the root collar diameter and carbon sequestration in the study area using data obtained from the interpretation of the crowns of 88 608 Siberian larch trees. It was found that in the ecotone of the upper boundary of tree vegetation on an area of 7.32 km², the aboveground and belowground phytomass of Siberian larch is 1355.2 tons of dry mass, which contains 677.6 tons of carbon, or 2484.5 tons of CO₂equivalent.