A little-studied, underground layer of rock may provide a vital reservoir for trees, especially in times of drought, report scientists funded by the National Science Foundation (NSF) and affiliated with The University of Texas (UT) at Austin and the University of California, Berkeley. The study, published today in the journal Proceedings of the National Academy of Sciences (PNAS), looked at the water stored inside the layer of weathered bedrock that lies under soils in mountain forest ecosystems.