Mangrove growth linked to 18-year lunar cycles

(ORDO NEWS) — Satellite observations have shown that increased levels of carbon dioxide in the atmosphere contribute to the growth of mangroves.

At the same time, the area and density of the forest crown fluctuate depending on the long-term cycles of the Moon’s orbital motion.

Mangroves grow in calm, sheltered tidal zones of tropical seas. These are evergreen deciduous forests that are home to a great variety of life forms.

In addition, they protect the coast from water damage, so the importance of mangroves is much greater than the rather modest area in which such thickets are found.

This forces scientists to take a closer look at them – and at the changes that climate change, ocean pollution and economic activity are causing in mangrove forests.

The new work of Neil Saintilan and his colleagues from the Australian Macquarie University is devoted to this.

Scientists analyzed long-term Earth remote sensing data collected as part of the Landsat project commissioned by NASA and the US Geological Survey.

Based on satellite imagery taken from 1987 to 2020, scientists have estimated how the area and density of mangrove forests along the coast of Australia has changed.

First of all, the authors noted that mangroves are growing ( some past studies have also indicated this). On large time scales, their spaces increase, which is most likely due to an increase in carbon dioxide in the atmosphere, an increase in sea level and average temperature.

However, when the scientists adjusted for this trend, they found fluctuations in the area and density of mangrove forests – cycles of about 18 years. This regularity brought to mind the natural satellite of the Earth.

The moon revolves around our planet approximately in the plane of the equator. However, its orbit fluctuates slightly from this position with a frequency of 18.6 years. These movements affect the height of the tides in many regions of the world.

The smaller the deviation of the lunar orbit, the greater the difference between the high and low waters of the semidiurnal tides.

It is these conditions that contribute to the temporary growth of mangrove forests. In the opposite phase of the 18-year lunar cycle, when the tides change again, the vegetation shrinks slightly.

Neil Saintilan and his co-authors are confident that these fluctuations also affect mangrove forests growing outside of Australia, as far as Indonesia and Vietnam.

Such changes are important to take into account in order to more accurately assess the response of mangroves to other processes, including climate change.

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