Why are the world’s tallest trees under threat?

The view might be good, but the outlook for some of the world’s biggest trees is far from rosy. Long-term studies of forests in Africa, Amazonia, and Central America have indicated that the tallest trees are now more vulnerable than ever.

Why? The answer is a mix of increased deforestation leaving tracts of woodland more fragmented, severe droughts, and new pests and diseases.

But don’t those things affect all the trees? Well, that’s true, but because of the unique characteristics of the tallest trees, they are being disproportionately affected. First off, being tall means that their trunks are having to support more weight than their smaller siblings. By Newton’s first law, every part of the trunk has to be able to support the weight of everything above that part. This means the bottom of the trunk needs to carry the weight of the entire tree. No wonder their trunks are so thick! This thickness in turn means tall trees tend to have stiffer trunks–trunks that when exposed to turbulent winds near the edge of forests can uproot.

In cloud forests, tall trees use their height to soak up water droplets from low-lying clouds. With global warming suspected of rasising cloud cover to higher elevations, tall trees lose this source of moisture, and may become more vulnerable to brushfires which occur in times of severe drought.

While the tallest trees enjoy the best of the sunshine, with canopies of enormous reach, aggressive invasive shrubs in the understoreys mean that the trees’ seedlings often cannot reach the forest floor and grow. With no replenishment of the species, the disappearance of the tallest trees is inevitable in this climate.

Why does all this matter? Well, aside from the stunning beauty of these trees, scientists are concerned that with up to 25% of the forest biomass locked-up in these trees, not only would their deaths mean vast habitat destruction, but also the release of large amounts of stored carbon. This release could further add to the greenhouse effect, leading to a “postive-feeback” loop of further climate destabilisation and more environmental destruction.

Can you guess the species, age, and location of the world’s oldest trees–which are often also the largest?

Image Credit: Wiki Commons

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