Estimating and simulation of stand features according to various climate scenarios of even aged pure eastern beech (Fagus orientalis Lipsky.) stands in the west Black Sea Region

The objective of this study is to estimate various stand characteristics of our main tree species, Eastern Beech (Fagus orientalis Lipsky.), which has an widely distribution in our country, under different climate scenarios, and to demonstrate the simulations of these characteristics. A total of 240 sample plot data were used in this study, which was taken to reflect the variability in growth and yield characteristics in Eastern Beech stands of the same age, natural, pure, and managed, within the Western Black Sea Region. These sample plots were selected with different stand ages, site qualities, and stand densities. In this study, several nonlinear regression models were developed utilizing the data mentioned earlier. These models include a distance-independent individual tree diameter increment model incorporating various individual tree and stand characteristics, climate variables such as annual mean temperature and annual total precipitation, a logistic function-based individual tree mortality model, a stand tree count model based on Gompertz (1825) nonlinear model structure, and a generalized height equation based on Schnute (1981) model. Using the "GenSa" package in the R programming language, a new distance-independent individual tree increment model was developed in a nonlinear regression model structure that includes the independent variables affecting the diameter increment of trees. In summary, the primary objective of this study was to develop various growth models, including individual tree increment and mortality models, using sample plot data from Eastern Beech stands in the Western Black Sea Region. Following the development of these models, were then integrated into a growth simulator system using the Visual Basic programming language for further analysis and simulation purposes. The developed growth simulator allowed the simultaneous operation of the sub-models, enabling the estimation and simulation of stand volume, basal area, mean diameter, stand biomass, and stand carbon properties for 16 different periods with 5-year intervals (2027, 2032, 2037, 2042, 2047, 2052, 2057, 2062, 2067, 2072, 2077, 2082, 2087, 2092, 2097, and 2102). The simulation values were obtained using future climate scenarios from Worldclim 2.1 and data sets of the HadGEM3-GC31-LL global climate model for three different climate scenarios (SSP 126, SSP 245, and SSP 585). This study identified significant differences were identified at a 0.05 significance level between the simulated stand properties and climate characteristics under the three climate scenarios (SSP 126, SSP 245, and SSP 585). When evaluating the homogeneous subgroups for these differences, it was determined that SSP 245 and SSP 585 climate scenarios were in the same group and similar in terms of stand properties, while the SSP 126 climate scenario had higher stand property values compared to the other climate scenarios.