Reforestation of Scots pine stands in the Luhansk region after Russia’s invasion of Ukraine: predictive modeling

Forests destroyed during the current Russian invasion in Ukraine require urgent restoration and renewal. Considering that the forests are still inaccessible due to the ongoing occupation, it is important to conduct computer simulations of their possible artificial renewal. For this purpose, Urban Forest Biomass (UFB) computer model was parameterized by means of the data from 60 sample plots (SPs) established in the Scots pine (Pinus sylvestris L.) stands growing in the Luhansk region in Ukraine and validated for two representative plots. The forests growing on two SPs selected for model validation were established in 2014. UFB model validation was made based on the data collected in 2021, and the prediction was made for 2030. The modeled tree height was highly correlated with values observed in the field in 2021 (R² = 0.9579, root mean square error [RMSE] = 0.0264, systematic error [BIAS] = 0.0013 for SP 1 and R² = 0.9601, RMSE = 0.0305, BIAS = 0.0164 for SP 2). The forecast of future forest development was conducted for high (SP 1) and low (SP 2) initial tree density. The simulation results for the current climatic conditions showed that in SP 1, up to 33.44% of planted Scots pine could die until 2030. In SP 2, the percentage of dead trees was lower (22%). In the warm-dry scenario, the simulations showed an increase in the percentage of Scots pine mortality up to 78% for SP 1 and 29.76% for SP 2. The predictions confirmed the hypothesis about the negative impact of high density on the development of planted trees and their increased mortality in the warm-dry scenario. The high autocorrelation of the analyzed number of Scots pine trees suggests their high growth potential in the research area. On the basis of the results obtained, we recommend planting of a relatively small number of Scots pine seedlings (3,333 individuals/ha) to ensure their greater survival in steppe conditions of East Ukraine under the influence of warfare and warm-dry climate change scenario.