We continue our look this week at mangroves, which are among the planet’s most threatened tropical ecosystems. We examine, exclusively, some of those threats below. Have questions, comments? Email Petre Williams at williamsp@jamaicaobserver.com.

THERE are a range of threats to mangrove forests in Jamaica and, by extension, the Caribbean and the world. They include over-harvesting, river changes, clearing, over-fishing, pollution, coral reef loss and climate change.

Over-harvesting

Mangrove trees the world over are used for firewood charcoal production as well as for construction wood and wood chips. While harvesting is a practice that has been ongoing for hundreds of years, it has got out of hand in recent times.

In some instances, faced with limited alternatives, if any, people in certain poor communities, such as St Thomas here in Jamaica, increasingly rely on mangroves for charcoal production, for example. The result is over-harvesting, which threatens the survivability of mangrove forests.

River changes

Dams and irrigation cause a reduction in the quantity of water that gets to mangrove forests, thus changing the salinity (salt) level of the water in the forests. Where salinity levels become too high, the mangroves die. Freshwater diversions may also threaten the survival of mangroves.

Erosion, which is caused by deforestation of land, may also deplete mangrove forests. This is so since deforestation increases sediment in rivers, which can undermine the mangroves’ filtering ability.

Clearing

This involves people removing the mangrove forests or sections thereof to facilitate the construction of housing solutions, agriculture production, and infrastructure development. In the last several years, the forests have been destroyed to accommodate tourist developments, such as hotels.

It is this fear that exists among members of the environment lobby group World African Reunification Solidarity Association (WARSA) regarding a proposal by state minister in the Ministry of Housing, Water, Transport and Works, Fenton Ferguson, to have a 600-room hotel built in St Thomas.

Meanwhile, clearing has been identified as contributing to the more than 35 per cent of global mangrove loss to date.

Pollution

Pesticides and other chemicals produced by humans to treat one thing or another can potentially wipe out mangroves. Such chemicals may be carried downstream, killing animals which call mangrove forests home. Oil pollution is also a threat since oil will choke mangrove roots, killing the trees.

Here in Jamaica, pesticides and other chemicals are utilised to treat organisms that threaten agricultural production. They become a problem for mangroves when farmers and others discard the empty chemical containers, which are washed via gullies or rivers to mangrove forests.

Loss of coral reef Mangroves function, importantly, as a barrier to strong waves that could destroy coastal settlements during, for example, a hurricane. As it happens, however, mangroves work in tandem with coral reefs to make this happen even as the latter serve the cause of survival for the former.

As such, it means that where coral reefs are destroyed, mangroves are left to take the brunt of the impact from the strongest of waves, which wash away the fine sediment in which mangroves thrive. The waves deter seedlings from taking root, even as they wash away nutrients that are important for mangrove ecosystems.

Some of this is evident as one examines a section of mangrove forests near the lighthouse in St Thomas. The section of forest there took the brunt of the impact from Hurricanes Dennis and Wilma in 2005 and Hurricane Ivan the year before.

Climate change

The survival of mangrove forests depends on stable sea levels. Unfortunately, with greenhouse emissions as high as they are, there is the climate change phenomenon to contend with. It is a phenomenon which, among other things, sees an increase in the earth’s temperature as well as an increase in sea levels.