Between Earth and Heaven

Trees are remarkable anti-gravity devices, capable of lifting water from roots to leaves without a pump. In some cases, the lifting heights are over a hundred meters. Even for much lower heights, the mechanism by which this is done remained a mystery until the end of the nineteenth century. The breakthrough was the development of the Cohesion-Tension theory, a quiet triumph of modern science and one which has seen significant advances since its conception. In Between Earth and Heaven: The Physics and Future of Trees, Harvey Brown explores the history of this theory and attempts to bring together the various scientific threads involved its articulation. He discusses the anomalous properties of water that are essential to the process of lifting and transpiration: the release of water vapour from leaves into the atmosphere. The physics involved in lifting water from roots to leaves, especially capillarity and osmosis, is explained in accessible terms. What is the future of trees in the Anthropocene? Understanding the hydraulics of trees helps to reveal the nature of the impact of global warming, deforestation, and degradation on the health of the planet's great forests. In the case of the Amazon rainforest, a sizeable region of the Brazilian sector has turned from carbon sink into carbon source.