Simulating the potential forest ranges in an old land: the case for Turkey’s forests

The central aim of this study is to estimate the current potential distribution of Turkey’s forests and their composition in absence of anthropogenic landcover change, and in this manner to contribute to past studies on the distribution of European forest taxa by filling an important spatial gap. For our simulations, we used high resolution climate data from ERA5-Land and a process based dynamic regional to global vegetation model (LPJ-GUESS), for which we modified the original European tree species list to match the climatic sensitivities that the species in turn exhibit throughout their natural ranges in Turkey, alternating between subspecies where necessary. This is the first application of LPJ-GUESS for the entire country using high resolution climate data. We defined the climatic tolerances for the model of three conifer species with wide distribution in Turkey: Pinus nigra, Pinus brutia, and Cedrus libani. We first identified relative bioclimatic tolerances of species for Turkey by way of comparing their current recorded distributions to ERA5-Land reanalysis data using observation data from the General Directorate of Forestry of Turkey, and later through ensemble runs with LPJ-GUESS we finetuned their parameters. Finally, we compared simulated net primary production to MODIS remote sensing observation estimates. In general, LPJ-GUESS captured the natural distribution ranges of different forest taxa, especially after the introduction of three additional species native to Turkey, highlighting competition for resources. Due to probable regional acclimatization of species, our final set of parameters for the different plant functional types offers a suitable alternative for future studies.