How Do You ReGrow a Rainforest? Send in the Tapirs.

A new study shows that the Amazon’s largest land animals are exceptional at dispersing seeds.

May 02, 2019
A South American tapir grazing in Mato Grosso, Brazil

Robert Harding/Alamy

The South American tapir is 600 pounds of wonder. At lengths of up to eight feet, tapirs are the largest terrestrial animals in the Amazon rainforest. They can swim like fish, climb mountains like goats, and pluck leaves and fruit off trees like elephants, thanks to a wiggly, prehensile schnoz.

Oh, and tapir poop may have magical, rainforest-rejuvenating properties.

This is not an infomercial. According to a new study published in the journal bioTropica, not only do tapirs pack a veritable garden of seeds in each deposit of dung, but they even prefer to leave these little plant bombs all over the areas of rainforest that need them most.

You see, people have been chipping away at the edges of the Amazon for decades. Felling trees for wood, paper, and other products fragments habitat, while fires clear the way for ranching and agriculture. But the flames can spread beyond where the farmers intend for them to go (as fires often do). Windstorms whip against the new edges of the forest, often dropping trees that would have otherwise been shielded. The fallen trees can become still more fuel for future fires. All of this creates a feedback loop in which the forest continues to shrink.

A fire set by farmers to level harvested crops burns through the Amazon rainforest near Boavista, Brazil

Nigel Dickinson/Alamy

Fortunately, it is possible to reseed the rainforests we’ve destroyed. Possible, but costly. One study found that for the Brazilian states of Mato Grosso and Pará to get their forests back to conditions outlined by the country’s Forest Code, the cost would fall between $2.6 and $6.3 billion.

But tapirs are perfectly willing to do at least some of that work for free, say the new paper’s authors.

Through a combination of camera trapping, scat collection, and remote sensing that makes use of laser pulses (known as LIDAR), the scientists have discovered that tapirs actually prefer disturbed areas of rainforest, perhaps because they are full of tender new plants sprouting out of the soil. And the more time tapirs spend digging around in the damaged areas, the more likely they are to drop a pile of poo.

To conduct the study, researchers collected tapir turds from three plots of land—one that is burned every year, one that is burned every three years, and an unburned control plot. They found that the never-burned and three-year plots had nearly the same amount of tapir droppings during the surveys (43 and 48 piles, respectively), while the patch of forest that had been flamed every year presented a whopping 72 piles.

The results got even more interesting, and stinky, when the scientists washed all of those samples through sieves. After tweezing out every itty-bitty seed, they learned that the forest giants were also delivering considerably more seeds to burned forest plots (48,406 for the three-year burns and 62,330 for the one-year) than unburned plots (just 18,468).

Not only did the tapirs deliver on quantity, but the quality of the seeds they provided was also top-notch. For starters, less than 1 percent of the seeds were damaged in some way after traveling down the animals’ gullets and through their intestines, which meant nearly all of them would have had a chance to sprout once they hit the forest floor. This finding runs counter to several other studies that suggest tapirs are crappy seed dispersers, either because their guts digest the seeds or because the animals often relieve themselves in water or seasonally flooded areas.

While it’s true that tapirs tend to poop in communal piles, or latrines, which limits the seeds’ dispersal, prior research has shown that these latrines do have their benefits. For one, they seem to protect seeds from hungry bruchid beetles. Furthermore, from a plant’s perspective, being encased in lots of fertilizer is usually a good thing.

And the kinds of seeds found within the feces is also beneficial. Forests grow in stages. After a destructive event like a burn, sun-loving pioneer species are the first to recolonize the area. That’s the easy part. What’s much more difficult is getting shade-tolerant “climax” species to take root.

Climax species, which tend to dominate in the later stages of succession, are crucial to the natural recovery of forests, says lead author Lucas Paolucci, an ecologist at the Federal University of Lavras in Brazil.

Amazingly, the tapirs in the study dropped around 120 times as many climax seed species as pioneer seed species, and four of the plant species found in the dung piles were not known to exist in the region. Tapirs are known for their ability to get around and have been documented plodding along for 12 miles. Taken together, these traits may allow them to play a critical role in mixing things up and creating biodiversity across a wide range.

A South American tapir and her young calf grazing together

IUCN Tapir Specialist Group,

So what’s the catch? Well, tapirs are in trouble. The International Union for Conservation of Nature classifies lowland tapirs as vulnerable to extinction due to habitat loss and hunting. Vehicle strikes and competition with livestock are also a concern. According to the IUCN, very little is known about the size of the lowland tapir population, but their numbers are thought to be decreasing.

“We worked on a privately owned farm,” says Paolucci. “There is no hunting there, so the animals are quite common.” Unfortunately, he adds, “this is not the reality for other regions in Brazil, especially in the Atlantic Forest,” where most Brazilians live.

In short, not only are we cutting up rainforests, which endangers the tapirs, but we’re actively hunting tapirs, which endangers the rainforests.

The good news: Conservation organizations have shown that it’s possible to reintroduce these animals to areas where they have been snuffed out, including the Iberá Natural Reserve in Argentina and the Atlantic Forest in the Brazilian state of Rio de Janeiro.

And now that we know such reintroductions are a two-for-one deal, perhaps folks in more locales will become interested in protecting tapirs and their life-bringing poo.

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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