The authors examine ecological and geophysical principles to explain how land far inland away from the ocean can remain moist, given that gravity continuously pulls surface and groundwater into the ocean over time.
All freshwater on land originates in the ocean from which it has evaporated, is carried on air flux, and precipitates over the land. Coastal regions benefit from this cycle by their proximity to the ocean, yet in the absence of natural forests in coastal regions precipitation weakens as distance from the ocean increases, leaving inland areas arid. The authors propose the concept of a biotic pump to explain how large continents can be sufficiently moist deep into the interior, and abundant with rivers and lakes.
Air and moisture are pulled horizontally by evapotranspiration over coastal forests. When water vapor from plants condenses, it creates a partial vacuum that pulls water evaporating from the ocean into the continental interior which results in forest rains. By contrast, deserts are unable to pull in ocean evaporation because they lack evaporative force.
Therefore, ongoing deforestation, especially coastal deforestation on a large scale, threatens to cut off rain to the interiors of Earth’s continents, thereby creating new deserts. The Amazonian rainforest is the prime example: Deforestation of the eastern coast of South America has led to changes in the rainforest that is resulting in drying and desertification of the interior, with unprecedented fires and loss of rivers. Historically, Australia’s interior became a desert around the time the first humans arrived on the continent, and the authors speculate that early coastal deforestation was the cause. On the other hand, restoring natural coastal forests can also restore inland water cycles and reverse desertification.
This article illustrates the importance of biological relationships that are ecologically complex and poorly understood. It highlights the significance of the precautionary principle in assessing what we don’t know when altering ecological processes, and taking preventive action in the face of uncertainty.