DAVID GREENE, HOST:
If you're in North Carolina or Tennessee and you drive into Great Smoky Mountains National Park, you might be awed by the trees. The forest glows in vibrant green. But many of those trees are actually sick, infected by deadly invasive pests. NPR's Nathan Rott met the people who are trying to keep the forest alive.
NATHAN ROTT, BYLINE: So we're looking for a tree?
MATT MOORE: (Laughter) Yeah, several.
ROTT: It's midafternoon, about 70 degrees outside, and we are hiking off-trail on the Tennessee side of Great Smoky Mountains National Park - uphill, over logs and through thick patches of brush.
This is an easy hike for Matt Moore and the park's vegetation crew, veg crew for short. They're wearing backpacks and carrying 5-gallon buckets filled with drills, tubing, pumps and pesticides, some of the many medical supplies of this nationally protected forest.
MOORE: You found it? Oh, Mylanta.
ROTT: The tree we hiked all the way up here for is - well, a tree. It's tall, but not particularly big. You could wrap your arms around it and still clasp hands. We'll get into the specific species and all of that stuff in a bit. But for now, let's do what we're here to do - treat this tree.
For this kind of treatment, the veg crew drills about six tiny holes into the tree around its base.
JESSE WEBSTER: Don't pump too much chemical through one hole.
ROTT: They then push skinny, metal spikes into each of those holes. All those spikes are connected by tubing, and a bicycle pump is connected to the other end of the tube system. It gets a few pumps, and a Kool-Aid blue pesticide works its way through the tubes into the base of the tree. Jesse Webster, the head of the veg crew, says this is what's called a tree injection system. Basically, they're giving the tree a shot to keep it healthy.
It really does look like an IV system that's hooked up to the tree.
WEBSTER: Oh, it's - we call them IVs. I mean, they're out doing a tree IV.
ROTT: Few trees get this intense of a treatment. Most just get sprayed with chemicals, which is less time-consuming. That's important logistically because there are a whole lot of trees in this forest that need treating.
Overall, the veg crew has treated more than a quarter million trees in Great Smoky Mountains National Park. They're easy to spot, Webster says, because they're the ones that are still alive.
WEBSTER: Any tree that wasn't treated in this park and has never seen a treatment is probably dead or closely or on the way out very soon, within the next 10 years.
ROTT: OK. So let's get off this hillside for a bit and talk a little more with Jesse Webster about the tree in question. It's an eastern hemlock. But we're just going to call it a hemlock from here out. Hemlocks range from Canada to northern Mississippi. They can live longer than 500 years. And they're known as the redwood of the East because of their size, height and gnarled tops.
They make up a significant portion of a lot of forests, but particularly so at Great Smoky Mountains National Park.
WEBSTER: One out of every 5 trees in the Smokies is a hemlock currently.
ROTT: And hemlocks serve a very important role in these forests.
WEBSTER: It's a foundational species. You know, people real familiar with keystone species.
ROTT: Like lions, wolves, sea otters - species that have a huge impact on the ecosystem around them - that's the hemlock in eastern forests.
WEBSTER: They moderate the highs and the lows of air and water temperature.
ROTT: Because of the shade they provide, they are nesting sites for birds. The list of things they do is long. But because of one nefarious little critter, hemlocks are dying off at a scary rate. Webster says without treatment...
WEBSTER: You know, we're looking at complete ecological extinction on our landscape.
ROTT: The reason for this die-off is a little aphid-like bug called the hemlock wooly adelgid. Native to Asia, the bug was first reported in the Eastern U.S. in the 1950s, but it spread primarily through the buying and selling and moving of firewood to 16 different states. Now in Great Smoky Mountains National Park, they are not hard to find.
WEBSTER: Here's the wee beastie.
ROTT: Oh, man. That's it.
WEBSTER: Yeah, so each light, fluffy mass you're seeing is an ova sac.
ROTT: It's like the end of a Q-tip, only way smaller, at the base of the outermost needles on this tree. And really, they look pretty harmless.
So we take an infected branch into a nearby research center to get a closer look under a microscope.
WEBSTER: So here's one.
ROTT: Webster takes a little metal tool and starts picking away at one of the white, woolly masses. There's a close-up image on a video display.
WEBSTER: Here's a mass. OK. Now you can look at this - a female that's still - was relatively still alive.
WEBSTER: They haven't darkened. These eggs haven't darkened.
ROTT: Inside is a cluster of eggs in a full-grown female adelgid. To the naked eye, she would be no bigger than a speck of dust. But up close...
WEBSTER: It's gnarly even up close.
ROTT: (Laughter) It is gnarly, man.
The female has attached herself to the base of the needle, where she's been feeding off of the tree's nutrients, keeping them from the tree itself. Multiply this by thousands, and you have a starved soon-to-be dead tree. Multiply it by millions - well, you have a dying forest. So how can you possibly deal with something like this?
Webster takes us to a place that might hold the answer, an insect nursery.
Those pesticide injections we heard about earlier only last five to seven years. These scientists are looking for something longer-lasting.
WEBSTER: So this is the baby predator beetle.
ROTT: Scientists have brought over a few different species of predator beetles from Asia that prey on hemlock wooly adelgids.
WEBSTER: This is a laricobious.
ROTT: They raise them at insectaries, insect nurseries like the one we're at now. And for those of you like me hoping to hear about some vicious, fanged-looking predator, sorry.
WEBSTER: These beetles, you know, they're pretty small.
ROTT: Really, they're no bigger than a pinhead and almost look like a roly-poly bug.
WEBSTER: How much of an effect can they have on this problem? Well, look at the adelgid. They're smaller than these.
ROTT: And one predator beetle can lay eggs on scores of adelgid egg sacs, killing all of them. Now, introducing any predator species to a national park is not an easy decision. But it's one that was made out of necessity. Hiking into the forest, treating trees every five years with pesticides really isn't a sustainable or practical practice, and it doesn't work at scale.
WEBSTER: Really, we're trying to set up that natural predator-prey balance, a sustainable system and then back away.
ROTT: The predator beetles will never eradicate the hemlock woolly adelgid. Webster knows that. But hopefully, it will help to slow the adelgid spread and give the Eastern hemlock and these forests a chance to adapt. Nathan Rott, NPR News, Great Smoky Mountains National Park.
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