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Anatomy of a forest after a hurricane

22 September, 2016 - 16:30 -- World Land Trust
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Tree damaged by hurricane
Trees felled by hurricane

At the beginning of August, the deadliest Atlantic hurricane of the decade spun through Central America, leaving a destructive wake of floods, landslides, power cuts and destroyed buildings. A state of emergency was declared in Belize and Mexico and international aid was sent to the area from the European Union, Taiwan, UNICEF and USA.

World Land Trust (WLT) launched an emergency appeal to support conservation partner Programme for Belize (PfB) as they recover from the damage caused by the violent tropical storm. PfB protects around 100,000 hectares (260,000 acres) of tropical forest in north-west Belize, the Rio Bravo Conservation and Management Area. This land was designated regions purely for conservation protection as well as buffer zones for sustainable logging to provide long-term income for the project.

There have been around 800 hurricane and tropical storm passages through the Caribbean over the last 100 years, so the forest ecosystems in this area have adapted to the passage of hurricanes over millennia of evolution.

Immediate effects: Opening the canopy

The storm’s path through a forest can be seen by dramatic destruction: the trees which are not uprooted or snapped are stripped of their leaves; bark is shredded by the wind and battered from sandblasting; rivers swell into standing floods and landslides reshape the landscape.

One of the most significant events of the hurricane which controls the way the forest reacts is the amount of leaf and dead tree matter which falls to the forest floor. It takes about ten months for leaf litter to decompose and enrich the soil with nutrients, which are taken up by seedlings. Often hurricanes are followed by fires, which spread more rapidly due to this dry material.

This is where forest ecology and forestry come into conflict, as foresters remove the fallen trees and branches, partly because some timber is still useable but also to reduce the fire risk. In the short term, fires can damage stands of high quality timber trees, but in the long-term fires boost soil fertility and create hollow, misshapen trees which provide niches for bats and birds to roost.

Re-organising the eco-system

The way hurricanes reshape forests has consequences for animal populations, especially birds. The hurricane passage can kill birds from exposure to extreme wind and rain, but it is thought that most of the fluctuations seen in bird populations are due to habitat change.

The elimination of the canopy shakes up the dynamics of the forest. Canopy-dwelling birds migrate vertically down the trees, bringing them into competition with ground-dwelling birds, and food shortages can cause migrations to different parts of the forest or even further afield in search of untouched habitat. Within the following year these migrating populations often reinvade their previous habitats, once the canopy has re-established, and avian populations return to pre-hurricane numbers.

Hurricanes as a tool of evolution

Aerial view of hurricane

The hurricanes sharpen the influence of natural selection on the environment. Over a third of the tree species in Belizean forests have evolved a suite of specialised adaptations which enable them to survive hurricanes and tropical storms which flatten the rest of the forest. These trees have to be able to withstand the severe winds, but also be quick to take advantage of the holes left in the forest by the storms by growing rapidly to replace the openings left by felled trees. One of these trees is mahogany, which has various hurricane adaptations such as flexibility, fire-resistance and the ability to grow quickly (which makes it light-timbered). These qualities have incidentally made it highly sought after for timber.

They also produce seeds every year, which is unusual for long-lived trees, and this means they are quick to take the opportunity to grow and fill the gaps left in the forest after a hurricane, racing other species to the canopy and access to sunlight. 

Climate Change

Hurricanes become part of the natural cycle of the forest, speeding up evolution and ecological creativity as species adapt to the disturbance. This could become more acute over the next century, as climate change may increase the frequency of hurricanes and the ability of the forest to adjust will be crucial in the survival of the ecosystem.

Roger Wilson, Director of Conservation at WLT and previously Project Manager for the Rio Bravo Forestry Programme, said “If the forest is hit more frequently, I think the forest itself will survive but I think there will be a lot of changes in the species. The tree species that are more hurricane adapted will survive and natural selection will take its course as these become the dominant species of the forest. A higher frequency of hurricanes will mean that the forest will change nature.”

More information

PfB logo

Programme for Belize (PfB) suffered major damage from Hurricane Earl to its offices and is now working to recover lost timber and reduce fire risk as well clear roads of debris to gain access to the forest and field stations. WLT has launched an emergency appeal aiming to raise £10,000 to support their recovery efforts.

Donate to the Belize Hurricane Emergency Appeal

References

Lugo, A. E. (2008). Visible and invisible effects of hurricanes on forest ecosystems: an international review. Austral Ecology, 33(4), 368-398.

Michener, W. K., Blood, E. R., Bildstein, K. L., Brinson, M. M., & Gardner, L. R. (1997). Climate change, hurricanes and tropical storms, and rising sea level in coastal wetlands. Ecological Applications, 7(3), 770-801.

Comments

Sounds like for the ecosystem, thehurricane can be as much an opportunity as a destructive event. Land use and land management positively directed can lead to improvements to the forest ecosystem

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