Tree rings reveal the adverse effect of water pumping on protected riparian Platanus orientalis tree growth

Abstract

The ongoing increase in human population and the subsequent freshwater demands raise conflicts regarding conservation of riparian ecosystems. Identifying anthropogenic effects on these vulnerable nature resources is crucial for preventing future damages. Here we measured tree-ring width and isotopic carbon composition (δ13C) in stem wood of protected Platanus orientalis trees at the Kziv Nature Reserve, a Mediterranean riparian ecosystem in northern Israel. In this reserve, water was pumped for human needs during 1976–2006 from the major spring feeding the stream. We show a negative exponential correlation between stem growth and pumped water amounts. Spring drawdown had a significant negative effect on growth even in years when amounts were reduced to ~2 ∙ 106 m3 year−1, leveling off at around 5 ∙ 106 m3 year−1. Precipitation and spring volume effects on growth were exposed only after pumping stopped, further indicating its role in inhibiting tree growth. During the pumping years, stem wood δ13C was up to 1.8‰ higher than after pumping cessation, indicating the drought stress imposed on trees. Our results provide an unequivocal evidence for the adverse effect of water pumping on riparian Platanus orientalis tree growth. Such effects, and their related tree mortality risk, must be considered in sustainable water management planning.