Transitioning: the role of disturbances on instigating cross-overs of vegetation zones (a biome perspective)

This study considers the potential shift of biomes due to simulated changes in climatic drivers up until the end of this century, and how these changes effect the frequency of disturbances which in turn may affect the ranges of vegetation life zones. The study area is mainly the Anatolian Peninsula and its immediate surroundings, a unique location harboring high species diversity and high rates of endemism. Forcing a global to regional dynamic vegetation model with five Global Circulation Model contributions to Coupled Model Intercomparison Project (CMIP6, bias-corrected with ERA5-Land), we looked not only at the changes in the distribution and composition of key forest taxa, but the range shifts of vegetation formations from a biome perspective (classified per The International Geosphere–Biosphere Programme’s nomenclature) focusing on transition zones. Our results simulated a potential increase in the ranges of all 4 woody biomes: forest, transitional woodland, woody grassland and shrubland, with a potential retreat in grasslands. This shift is continuous throughout the simulation period of 1961-2099, with the Central Anatolian grasslands being taken over by tree taxa – comprised mostly of pines and oaks – even for the historical simulation period (1961-2021), but more significantly towards the end of the century. From a biome perspective, the increase in forest biomass and the retreat in grasslands is somewhat contrary to expectations that dryland mechanisms will become more common even in mesic environments as climate change progresses, however in line when we look at the overall picture from a taxon-specific perspective, as species that make up the composition of the simulated woody grasslands in Central Anatolia are mainly drought resistant taxa. One potential reason behind this woody plant encroachment may be the changes in fire frequency and intensity in the absence of anthropogenic interference. Our ongoing research is focusing on this curious pattern as we further analyze this phenomenon with more detailed climate input data with different time windows and with a special focus on disturbances.