An insidious foreign foe is taking root in Mammoth Cave National Park and spreading its seeds.

The fast growing, odorous &#8220Tree-of-Heaven,” also known as Ailanthus, has been in the park for at least 30 years, but it’s grown increasingly hostile, threatening native vegetation with thousands of sprouts. Ailanthus can quickly overtake patches of parks, producing toxins that stifle other plants – and its root system is thick enough to damage sewers and foundations, according to park officials.

&#8220It’s odd that they are the Tree-of-Heaven, but they are such an evil tree,” said Vickie Carson, the park’s public information officer.

In July, nearly a dozen workers staged an all-out assault – equipped with herbicides and chainsaws – on the Chinese import at nearly 30 sites in the park. Thousands of Tree-of-Heaven stems were cut and treated with toxic chemical brews, although park defenders were careful not to affect the enemy’s peaceful, indigenous neighbors. About 50 of the invaders were 30 to 80 feet tall, but most were less than 10 feet, Carson said.

Biotechnician Nathan Talley, one of the park’s Tree-of-Heaven combatants, said staff try to eradicate all kinds of exotic trees, like garlic mustard and Mimosa, because they &#8220out compete the native species.” Ailanthus is the park’s most prolific pest.

Native park species grow gradually and have natural controls, but Ailanthus is persistent and spreads a lot of seeds, which remain fertile for a long time, he said.

&#8220Once you treat an area, you can’t just walk away from it,” Talley said.

The tree appears very smooth from a distance. It has thick branches with leaves that look similar to a black walnut’s, only longer and with more leaflets. Many Ailanthus clumps can be seen growing along Interstate 65 and Hwy. 90, he said.

&#8220It has a very distinctive smell,” Talley said. &#8220Some people have likened it to burnt peanut butter.”

He invited those unfamiliar with that scent to use their imaginations.

Talley’s colleague, botanist Adam Dattilo, said the smell is rancid, something people will always remember upon first sniff.

&#8220It’s kind of hard to discuss Tree-of-Heaven in the context of a single tree,” Dattilo said.

Unlike typical trees, like an oak, Tree-of-Heaven isn’t content with one stem. Instead, Ailanthus can produce hundreds in a short time and its seeds travel by wind and animals, he said.

The tree was introduced in the United States by Chinese settlers in the 1800s. In going west, they started carrying lots of Tree-of-Heaven seeds, he said.

The Chinese, who’ve written about it for thousands of years, have attributed medicinal qualities to Ailanthus, which is well-known throughout Asian cultures, Dattilo said.

In the Southeast United States, the tree is thought of as an &#8220edge species” that infiltrates forest openings. Ailanthus was used in the nursery trade for years and thrives in harsh conditions and urban areas, he said.

When Tree-of-Heaven is sighted at Mammoth Cave, staff try to pinpoint it for spraying using geographic-information technology, he said.

Park staff ask visitors not to bother the evil trees, but to inform workers, who can positively identify the enemy, of possible locations for removal.

&#8220I personally think there is a great threat,” Dattilo said.