The shiny leaves and branching roots of mangroves (红树林) in Australia are eye-catching, and now a study provides us with new findings about the trees. Long-term tidal cycles (潮汐周期), in large part, set in motion the expansion and contraction of mangrove forests by the moon drive, researchers report in Science Advances. This discovery is key to predicting when mangroves are most likely to grow fast.
Mangroves are coastal trees, which are good at absorbing carbon and could help fight climate change, that provide habitat for fish and fight against erosion (侵蚀). But in some places, the forests face plenty of menaces, including coastal development, pollution and land clearing for agriculture. Neil Saintilan, an environmental scientist in Sydney, worked out how the size and thickness of mangrove forests across Australia changed over time.
Saintilan noticed a curious pattern. Mangrove forests tended to expand and contract in a certain manner. "I saw this 33-year regular change, " Saintilan said.
That regularity got the researchers thinking about the moon. Over the course of 33 years, the plane (平面) of the moon's orbit around Earth slowly tilts (倾斜). When the moon's orbit is the least tilted relative to the equator, semi-diurnal tides (半日潮)—which consist of two high and low tides each day—tend to have a larger range. Saintilan found that mangrove forests experiencing semi-diurnal tides tended to be larger and denser precisely when higher tides were expected based on the moon's orbit, which could deliver much more water and necessary nutrients to mangroves.
It is important to recognize this effect on mangrove populations. Such knowledge could inform efforts to protect and restore the forests, thus promoting the growth of these trees. That might look like added limitations on human activity nearby that could harm the forests. But people should be more reactive.
