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Trees enemies help tropical forests preserve their biodiversity



Tropical forest diversity. Credit: Oregon State University

Scientists have long had trouble explaining how tropical forests can preserve their amazing variety of trees without a handful of species taking control ̵

1; or that many other species are becoming extinct.

The answer, researchers say, lies in the earth, which is near individual trees where natural "enemies" of tree species live. These enemies, including fungi and arthropods, attack and kill many of the seeds and seedlings near the host tree, preventing local recruitment of trees of the same species.

Seed distributors also play an important role in the dynamics of the tropical forest. Seeds from single trees that are transported far away – often from rodents, mammals or birds – have a chance to establish themselves as fungi and arthropods target different species in the new region. This restriction on the recruitment of trees near mature trees leads to a long-term stabilizing effect that favors rare species and hinders common species, the researchers said.

By reversing the previous theory, the researchers show that these interactions with enemies are important enough to preserve the forest's incredible diversity of tropical forests. The results of the study will be published this week in . Procedure of the National Academy of Sciences ( PNAS ).

"In many North American forests, trees compete for space and some have competition." A niche that allows them to outdo others, "said Taal Levi, Oregon State University ecologist and lead author of the study," Douglas Firs are Species that grow best after a fire. Hemlock thrives in the shade and grows well under a canopy. Some species are good at altitude.

"But in the tropics, all tree species seem to have a similar competitive advantage.There are a multitude of species, but only a few individuals of any kind.The chances of blinding out should be high, but there must be a mechanism that prevents them a species becomes general and dominates, and these natural enemies have a high host specificity. "

Egbert Leigh, of the Smithsonian Tropical Research Institute, best describes the diversity of tropical forests in a statement:" How can a half square kilometer (from the forest )) in Borneo or Amazonia there are as many tree species as 4.2 million kilometers of forest in temperate zones in Europe, North America and Asia taken together? "

Levi said that in some tropical forests up to 1,000 different tree species lived in a common area Notion of natural enemies that limit the recruitment of juvenile trees is not new and has been nearly halfway It was set up by two scientists in the so-called Janzen-Connell hypothesis.

Although Janzen-Connell effects were supposed to prevent the adoption of one species, they do not explain how a thousand tree species can be held together, and other scientists claimed that the Janzen-Connell effects could only be preserved. There are only a few species and was therefore relatively unimportant for the preservation of the diversity of tropical forests.

Instead, Levi and his colleagues from the University of Florida in Oregon and James Cook University in Australia say this close relationship between trees and their natural enemies are the key to the diversity of tropical forests. They found that when fungi, arthropods and other natural predators create even small zones around trees where no new tree of the same species can establish itself, the very high tree diversity observed in tropical forests can be maintained almost indefinitely.

"There is a" seed shadow "around adult trees and some escape the curve and get out, allowing for recruiting in other areas until the host-specific enemies have established themselves at the new location," Levi said. "Therefore, maintaining the biodiversity of birds and mammals in these forests is crucial, otherwise recruitment will decrease – especially in over-hunted areas."

Levi is in the Department of Fisheries and Wildlife of the State of Oregon State of Agricultural Sciences.


Explore further:
"Cryptic" interactions lead to a decline in biodiversity near forest fragments

Further information:
Taal Levi el al. "Tropical Forests Can Maintain Hyperdiversity Due to Enemies", 19459016, PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1813211116

Magazine Reference:
Procedure of the National Academy of Sciences

Provided by:
Oregon State University


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