In their travels around the world, to places no one had gone before, old-era naturalists were amazed to discover enormous plant species in the tropical regions, and in other exotic places, and they could not explain why this was happening. Now, researchers have managed to finally elaborate a theory that explains why trees are, on average, a few centimeters in height in Greenland, while they grow to 100 meters and even more in tropical regions, and around the Equator. For the new research, investigators analyzed the geographical locations of some 7,000 plant species.

According to the preliminary results of the investigation, the trees at the Equator are, on average, about 30 times taller than those at extremely high altitudes. The investigators have also been able to determine that the amount of water that falls from the skies in the most rainy month of the year is a clear predicator of how tall the plants in the region will grow.

As an example, they say, few dwarf tree species live at the Equator, while virtually no large trees endure at high latitudes. Also, it would appear that rainfall is far more important than soil fertility or other factors in predicting plant sizes.

The researchers themselves have been very amazed to learn that such a clear trend exists among all plants in the world. The fact that trees are smaller as you travel North is no secret to anyone, but discovering that exceptions to this law were fewer than they imagined – that is, almost non-existent – really surprised the research team. “It might seem obvious that plants are taller in the tropics, after all tropical rainforests are clearly taller than Arctic tundra,” University of New South Wales scientist Angela Moles said, quoted by the BBC News. The Australian researcher has been the lead investigator for the study.

“However, there are plenty of tropical ecosystems that are dominated by short plants, such as savannas, and plenty of high-latitude ecosystems that are dominated by very tall plants, such as boreal forests,” she explained, adding that, incidentally, the largest and tallest plants in the world did not live anywhere near the tropics. “The tallest plant species on earth is the coast redwood, from California, which grows over 100m tall and the tallest flowering plant is mountain ash, which grows in southern Australia,” she shared.

“We thought that very cold or very dry ecosystems would lack tall plants, but there would be short plants just about everywhere. Instead, there turns out to be a remarkable scarcity of very short plants in very warm, wet, productive environments like rainforests. We hadn't predicted this, but in hindsight, it seems likely that in these highly productive ecosystems it is just so dark at ground level that there aren't many species that can actually make a living on the forest floor,” Moles concluded.