Tropical trees use social distancing to promote forest diversity

In a revelation that adds a new layer to our understanding of biodiversity, researchers at The University of Texas at Austin have found that tropical trees might be implementing a form of botanical “social distancing” to maintain a rich diversity of species. 

The study, published in the journal Science, proposes an intriguing explanation for the remarkable coexistence of hundreds of tree species in a single square mile of tropical forests. This has been a long-standing ecological puzzle that has confounded scientists.

Studying tropical trees and forests

Using computational modeling and data collected over three decades, the researchers conducted their study. The experts discovered a fascinating aspect of the spatial distribution of adult trees in a Panamanian forest. 

Surprisingly, researchers found these trees to be three times further from other adults of the same species than expected. This goes against the common saying, “the apple doesn’t fall far from the tree,” which suggests that offspring tend to settle close to their parent tree.

Annette Ostling is an associate professor at the University’s Oden Institute for Computational Engineering and Sciences and the Department of Integrative Biology. Working together with postdoctoral researcher Michael Kalyuzhny, they focused their study on a forest research plot equivalent in size to 100 football fields. 

What the study revealed

The research site is located on Barro Colorado Island in the Panama Canal. It has been under scientific scrutiny for the past 100 years. The investigation revealed that the spatial distribution of the trees far exceeded the typical dispersal distance of seeds.

“This is a stepping stone to understanding the dynamics of things like carbon storage that matter in relation to climate change,” said Ostling. “It’s such a fundamental question that, even if the applications are not yet known, there’s still a lot to learn, and this is one ingredient in understanding.”

The strong tendency of juvenile trees to establish themselves away from their parent tree puzzled the researchers. They proposed that the only theoretical explanation for such behavior is the presence of factors that discourage them from settling near their parent tree.

Making room for other tree species

The computational models suggested that each tree species likely experiences more adverse effects from its own kind than from other species. Researchers hypothesize that species-specific threats such as fungi or insects cause this phenomenon.

These antagonists, by hindering the growth of young trees near their parent tree, inadvertently “make room” for other species to establish. The resultant landscape is a forest rich in species diversity, with no single species dominating.

“Due to an abundance of available data on this particular forest, we knew the exact location of every tree and also how far seeds travel,” Kalyuzhny said. “We were able to ask: How should the forest look if trees just established where the seeds fell? With our computational models, it turned out that the real forest does not look like this at all – the real trees are much more far apart.”

Implications of the study 

This research is a significant step forward in understanding species diversity. It comes at the perfect time, when the world is experiencing a mass extinction. The team’s work bridges the gap between contrasting theories on forest formation and equips scientists with critical tools to learn how tropical forests and their inhabitants evolve over time.

“Trees are the engineers that provide resources for the entire ecosystem, and since most of the species in the world reside in the tropics, we must better understand what maintains the biodiversity of planet Earth,” said Kalyuzhny. 

“Many medications are sourced from the tropics, including thousands of substances with anti-cancer activity. The research digs into this fundamental question about the natural world.”

More about tropical trees 

Tropical trees are an essential part of the world’s biodiversity. They are found in the tropics, a region of the Earth near the equator that experiences warm temperatures throughout the year. This region includes parts of South and Central America, Africa, Asia, and Australia.

Carbon cycle

Tropical trees are known for their diverse species and are critical to the global carbon cycle. They play a crucial role in absorbing carbon dioxide and releasing oxygen. This makes them vital to human survival and combating climate change.

Size

Some tropical trees, like the kapok and the ceiba, can reach astonishing heights, often growing over 200 feet tall. Their thick, large canopies provide habitats for a myriad of other plant and animal species.

Leaves

Tropical trees often have broad leaves to maximize photosynthesis, given the abundant sunlight in these regions. Many species also have buttress roots. These are large, wide roots at the base of the tree that provide support to the tall and heavy trees, helping them extract nutrients from the often nutrient-poor tropical soil.

Fruits 

Tropical trees also produce a variety of fruits that are essential to the local ecology and economy. These include bananas, cocoa, coffee, mangoes, and many others.

Unfortunately, tropical trees are under threat due to deforestation, often driven by agriculture, logging, and mining. This deforestation not only endangers the trees themselves but also the countless species that depend on them for survival. 

Protecting tropical trees and the rainforests they inhabit is a crucial task for maintaining global biodiversity and climate balance.

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