Human influence at the Holocene treeline in the Julian Alps, Slovenia

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Fluctuations in timber/treeline have largely been subjected to past climatic changes; but throughout the Holocene humans became one of the leading drivers of these changes. By understanding the reasons for timber/treeline changes, we retraced past climate variability and/or anthropogenic impact on the alpine environment. This study focussed on the sedimentary sequence of the Lake ‘Jezero v Ledvicah’ (Julian Alps, Slovenia), which is currently located at the treeline and covers the last ca. 6200 years. We used mineralogical and geochemical analyses to understand sedimentary changes in the lake and its catchment area. By combining this dataset with palynological data we tracked the causes of vegetation changes with a focus on human impact. Geological analyses indicate slow continuous and undisturbed sedimentation with a combined biogenic and detrital calcite input throughout the Holocene. High percentage of clay minerals indicate that they were eroded from the catchment bedrock and/or were brought to the catchment indirectly by wind. The palynological results indicate that area around the lake was forested around 6200–4300 cal. BP, with predominant occurrence of coniferous taxa. Infrequent but fairly continuous grazing indicators during this period suggest a human presence in the highlands. By 4300–1100 cal. BP, the human influence in the area increased, resulting in a gradual decrease in tree taxa. Since 1000 cal. BP relatively open landscape developed with increased grazing indicators suggesting a continuous use of highlands.