Climatic and anthropogenic influence on tree-ring growth in riparian lake forest ecosystems under contrasting disturbance regimes

Abstract In the Mediterranean region, the coupled effect of recent changes in climatic features and an increase in human-related water demand induced a progressive reduction in the water level of many lakes. Consequently, intense withdrawals for public supply can affect the health of lake ecosystems and increase trees’ vulnerability to predicted drought intensification effects. This study aimed to evaluate, through a dendroecological analysis of riparian trees, the strength of the climatic and hydrological signals retained in the tree-ring widths and to detect a critical water-level threshold affecting tree resilience and growth recovery. Our study area is located within the Regional Natural Park of Bracciano-Martignano in central Italy. In recent years, the lake water-level drop observed at Bracciano after intensive water withdrawals raised concerns about the ecological impacts on the ecosystem's vulnerability. The main distinctive pattern in the climate-growth relations was the influence of previous years precipitation and drought conditions up to five years at Bracciano. At Martignano, where lake water withdrawals are absent, long-term climatic signals disappeared after two years. The intensive human water use at Bracciano Lake most likely induced trees to be more dependent on groundwater raising or soil water content stored from the previous rainy periods especially on an annual scale. On the other hand, tree-ring growth was strongly correlated with short-term water-level fluctuations (monthly – seasonal). Tree-rings of riparian species appear to be a useful tool to detect critical water levels after the intensive water withdrawals and the increase in dry conditions occurred in the past few decades. Yearly values ranging from -108 to -139 cm may be considered as potential thresholds affecting riparian species. This finding may support lake water withdrawal regulation for riparian ecosystem protection and conservation under future drought intensification.