Giant Trees Discovered in Africa

As far as tall trees are concerned, Africa has long been excluded from the list... until now. During a recent botanical survey of Mt. Kilimanjaro, a research team located a stand of large trees tucked away in a remote valley. Some of these trees were giants.

Tall trees are the result of a perfect storm of evolutionary history and unique environmental conditions. From the redwoods of the Pacific Coast to the Eucalyptus of Tasmania, rich soils, low levels of disturbance, and competition for light have driven some species to grow to mind boggling proportions. It seems fitting then that Africa's tallest mountain was hiding its tallest trees all this time. 

The species in question is known scientifically as Entandrophragma excelsum and belongs to the mahogany family (Meliaceae). A total of 13 giant E. excelsum were found during this expedition. Heights ranged from a modest 53.7 meters (176 ft) to a staggering 81.5 meters (267) in height! Unlike other species in this "Tall Tree Club," E. excelsum produces wood of surprisingly low density. However, it is thought that this low density wood, which is much less costly to produce, allows the trees to grow quick enough to avoid being overrun by vines before it can make it to the canopy. Indeed, very few E. excelsum were found to have vines growing on them. 

Although these are nowhere near the tallest trees in the world, they nonetheless break the African tall tree record, which was previously held by a non native Eucalyptus that died in 2006. The reason these African giants were not found sooner has to do with the remote region in which they grow. The area around Mt. Kilimanjaro has not received much attention from botanists in the past, having been overshadowed by the biodiverse Eastern Arc Mountains further south. 

Aside from discovering these trees, botanical surveys of Mt. Kilimanjaro are revealing this region to be just as biodiverse as the Eastern Arcs. Sadly, because of its long history of agriculture and more recent history of illegal logging, the rich forests of Mt. Kilimanjaro are quickly disappearing. The research team stresses the need to protect this area before one of Africa's biodiversity hotspots, as well as its tallest trees, are lost forever. 

Further Reading: [1]

Why Trees?

Walking through the forest is my favorite activity in the world. It is where I feel truly myself. There is something about towering trees that calms me. The thought of why forests are even there often jumps to mind during my strolls. Plenty of plants seem to do just fine hanging out closer to the ground. Why have trees (and some forbs) taken to this vertical realm. Why do forests exist?

In essence, forests are a prime example of an evolutionary arms race. It is one that these organisms have been fighting since the Devonian, roughly 385 million years ago. As plants left the water and began covering the land, some inevitably grew taller than others. There are pros and cons to growing tall. Competition is likely the prime driver for most tree species. Getting above your neighbors means more sunlight. Not every plant is as content as an herb to live out its life in the understory.

Height also means better pollinator visibility and seed dispersal for many tree species. Out in the open, gametes and propagules can be carried great distances by the wind. Colorful blooms would prove to be more exposed and easier for pollinators to locate. Growing tall can also get you out of harms way, removing sensitive growing parts from many different kinds of hungry herbivores and all but the worst forest fires.

There are many downsides to growing tall as well. For one, trees are exposed to the elements and are often victims of strong winds or lightening strikes. What's more, all of that wood takes a lot of energy to produce and, at least for most species, gives nothing back in the way of photosynthesis. It is a rather hefty investment. However, the cost of getting shaded out by your neighbors is definitely not worth the risk of staying small for sun-loving species.

Pumping water is another serious issue. The laws of physics suggest that redwoods are pushing the limits for how tall a tree can grow and still be able to lift water to leaves way up in the canopy. Of course, humidity can assist with such issues but for a majority of the water needs of a tree, water must be able to travel against gravity via weak hydrogen bonds. Water forms an unbroken chain within the vascular tissues of plants. As it evaporates from the leaves, it pulls more water up to fill in the void. It is possible that in today's world, a tree would not physically be able to grow much over 400 feet.

Despite the seemingly lavish waste of limited resources that a forest of trees would suggest, they are nonetheless a common occurrence all over the globe and have been for millions of years. The pros must certainly outweigh the cons or else tallness in trees would never have evolved. The next time you find yourself hiking through a forest, think of how the struggle for survival has led these towering organisms from lowly green stains on rocks to hulking behemoths racing towards the sky.

Further Reading: [1] [2] [3]