A new study suggests that planting vegetation to protect coasts from natural disasters may damage native ecosystems

Bioshields under the spotlight

Since the Indian Ocean tsunami of 2004, international bodies have invested heavily in planting coastal vegetation to act as ‘bioshields’ against natural disasters. As a result, non-native species have been introduced along many of the world’s coastlines.

The argument for planting bioshields is based on previous research that demonstrated that coastal vegetation reduces the impact of waves, provided that they have a relatively short wavelength. However, in a storm surge or tsunami the water level rises over a much longer period of time and is more similar to a tide than to normal wave patterns.

The study, ‘Shelter from the storm? Use and misuse of coastal vegetation bioshields for managing natural disasters’, was published in the scientific journal Conservation Letters. It looked in particular at an area of India where vast numbers of exotic trees, mainly Casuarina equisetifolia, have been planted as bioshields.

Not only are the local communities divided over the plantation (the trees are useful for firewood, but fishermen are unhappy that it’s now harder to reach their boats), but the bioshields have invaded native ecosystems such as mangroves. What’s more, sand dunes have been flattened to make way for the plantations, destroying nesting sites for sea turtles.

The researchers suggest that the planting of bioshields has been driven more by politics than by science, and that they are sometimes used as a substitute for emergency preparations, early warning systems and shelters. To counter this, they have created a decision tree for policy makers to ensure that bioshields are used appropriately.

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