Transcript

This is the Connection. A Dirty Freehub podcast connecting gravel cyclists to where they ride through short stories about culture, history, people, places in lands.

On this episode, we have created a deep dive of the dwarf missile toe in Oregon, unpacking ecology and management of this wild plant. David Shaw is a professor emeritus in the College of Forestry at Oregon State University. Before retirement, he was a forest health specialist with forestry and natural resources, director of Swiss needle ca Cooperative, and a professor of forest health in the Department of Forest Engineering Resources and Management at Oregon State University.

Dwarf mistletoe is what biologists refer to as a hemi parasite. The prefix hemi means half, so it is a parasitic flowering plant, but because it actually has a little bit of green coloration, it can [00:01:00] photosynthesize tiny fraction of its own carbon.

However, it relies heavily on a host, specifically conifer trees to survive and thrive. It steals the vast majority of its water and nutrients directly from a living tree. Let’s unpack this because its physical appearance is completely unexpected. when you hear missile toe, you probably picture those broad distinct green leaves and white berries.

That’s the classic image. But dwarf missile toe is microscopic by comparison. Barely even has leaves. Just these reduced tiny scale like bumps, and the flowers are completely inconspicuous, It is designed to be highly effective at its specific biological imperative.

What’s fascinating is how it achieves that imperative without the help of the usual suspects. Most missile toes rely on birds. The birds eat the berries fly to a new tree, leave their droppings, and the seed is planted. Oregon’s dwarf missile toe, has evolved an entirely different, highly kinetic method of spreading.

This plant has a built-in cannon. It shoots its seeds explosively. picture yourself [00:02:00] hiking through a serene, quiet Oregon forest. You’re taking in the fresh air, enjoying the silence, but meanwhile, there’s microscopic botanical artillery warfare happening right above your head.

The physics and biology behind this dispersal mechanism are incredibly complex. As the seed matures inside the fruit, internal water pressure builds up to an extraordinary degree,and then it just pops. And it violently discharges the seed. These tiny projectiles can be shot up to 35 feet away from the parent plant That’s the length of a school bus. It is just from built up water pressure. It is a massive distance for something so small.

Initial velocity can be over 60 miles per hour. the mechanism gets even more sophisticated than that. The seeds are coated in a highly specialized, sticky substance called Sen Vien. Think of vien as a natural biological super glue as the seed is flying through the air, if it makes contact with the needles or the branches of a neighboring conifer tree, this vien allows it to instantly adhere.

So it’s basically a sticky bomb. [00:03:00] Exactly. Now, on very rare occasions, a seed might happen to stick to the fur of a passing squirrel or the feathers of a bird, and it can be transported longer distances that way, The explosive discharge is the primary driving engine of how this plant moves through a forest canopy.

Okay, so it shoots through the air at 60 miles an hour and super glues itself to a branch. But how does it actually get into the tree? the reality is that the bark usually wins. If it hits the main trunk of an old growth tree, it’s game over.

It can only successfully infect young, thin, barked branchlets, so it needs to find the new growth, hit the precise, vulnerable, new growth of the tree once it lands on a suitable spot. The seed germinates and forms what is called a hold fast,A physical anchor that grips the bark.

From there, the plant branches out directly into the host tissue. It develops an endophytic structure. Endophytic means it lives entirely within the plant. This structure acts like a root system, digging deep into the inner living bark of the host tree. The missile toe [00:04:00] creates microscopic structures called sinkers

These sinkers position themselves right at the cambium, the growing layer of the tree, and then the missile toe weights as the tree naturally grows and adds a new ring of wood year after year. It grows around the sinkers. The tree essentially swallows the parasites, feeding tubes, embedding them deep within its own structure.

That’s incredibly sneaky. It is. This process is so slow and methodical that it takes anywhere from one to six full years before the dwarf missile toe finally gathers enough energy to push its tiny aerial shoots out through the bark to reproduce. And that kind of slow motion invasion explains a lot about its geography too, because Oregon is a massive.

Incredibly diverse state, and we aren’t just dealing with one monolithic plant here. Not at all the source notes. There are 10 distinct species of dwarf missile toes scattered across Oregon.

If we connect this to the bigger picture, the geography reveals a highly specific quirk in the northwest corner of the state, If you find yourself in northwest [00:05:00] Oregon, specifically west of the Cascade Crest and in the coast range north of Lane County, the landscape changes dramatically.

In that entire lush, rainy region, there is only one species of dwarf missile toe to be found. The hemlock dwarf missile toe correct and true to its name, it primarily infects western hemlock trees and occasionally true furs. But what at least completely alone, are the Douglas Fs in northwest Oregon.

The Majestic Douglas Fs are completely unbothered by missile toe, because the Douglas Fs elsewhere aren’t so lucky. While those Northwest Oregon Douglas Fs are perfectly safe, the Douglas Fs growing in Southwest and eastern Oregon are heavily targeted.

But they aren’t targeted by the hemlock missile toe. They are infested by a completely different species, aptly named the Douglas Fir dwarf missile toe,

it can only survive if the biology of the host tree is compatible on a cellular level. It’s like an organ transplant. Biologists have classified host trees into a strict hierarchy based on their susceptibility.[00:06:00]

You have principal hosts, secondary hosts, occasional hosts, rare hosts, and finally trees that are completely immune. It’s amazing just how picky this parasite is. For instance, the research gives examples for the Western dwarf middle toe. It will devour a Ponderosa Pine or Jeffrey Pine.

Those are its principle hosts. But if it lands on a knob cone or a Colter pine, it’s a secondary host. It’ll take them if it has to. Lodgepole and grape pines are just occasional hosts getting less and less ideal. And if it lands on a sugar pine.

It barely survives. That’s considered rare. And if that sticky seed hits any other conifer or an oak tree or maple, it just dies. The tree is completely immune. And that concept of immunity creates a shield effect in the forest, Imagine in an infected western hemlock tree.

It’s actively shooting its seeds in every direction, But if that hemlock is completely surrounded by Western red cedar trees and western red cedars are naturally immune to hemlock dwarf missile toe. Those cedars act as a physical [00:07:00] wall, nature’s own quarantine wall exactly.

The seeds hit the cedar branches stick to the needles, fail to germinate and quietly die. The Cedars completely block the explosive spread, protecting the rest of the hemlock trees further out in the forest. Okay, so we know how it spread so we know who it targets. Let’s talk about what this actually looks like, because if it takes up to six years for those tiny 10 inch chutes to finally pop out of the bark, how do you even know a forest is infected?

You can’t spot a 10 inch twig on a 200 foot tree from the ground. You can’t see the plant itself. But the visual symptoms of the infection are quite dramatic. when the missile toe first infects a branch. The tree reacts to the invasion. You will often see a small spindle shaped swelling at the site of the infection.

As the parasite establishes itself, it alters the tree’s hormones. This leads to chaotic branching at that specific spot, So it messes with the tree’s, hormones, and hijacks. Its ability to grow straight and tall.

Right?The tree’s main leader chute stops dominating the growth. Instead of focusing energy on reaching for the [00:08:00] sunlight, all this chaotic growth energy gets funneled into that single infected branch. It just pours all its resources into the parasite.

It results in a classic, deformation known as a witch’s broune. A witch’s broune. What? Perfect evocative name for it. It looks exactly like it sounds, this dense, tangled, chaotic mass of branches. It can be quite striking, and the scale of these things is staggering In a Douglas Fir, these witches brooms can grow bigger than a van or a large car suspended hundreds of feet in the air.

massive car size clumps of twisted wood hanging in the canopy. Now in pine species, the source says the brooms are more subtle, like strange little shrubs growing on the branch, but either way, it completely warps the tree. they demand a huge amount of the tree’s resources.

Generally, a heavily infected tree will have a significant portion of its crown filled with these witches brooms, Because the missile toe is hoarding all the water and nutrients. You might also see a dead tree top and an overall stunted deformed shape. But I must add a note of caution here. As an [00:09:00] observer or a researcher, you can’t just look at a clump of branches and declare its missile toe. Other native fungi, rus and even simple genetic growth anomalies can cause conifers to form similar looking witches brooms. To confirm dwarf missile toe, you have to lay eyes on those tiny aerial shoots, which is hard when they’re up that high, because these infections are often high up in the crowns of very tall, deformed trees with dead tops.

You need a good pair of binoculars and a lot of patients to spot them. We have a parasite that shoots biological super glue out of a cannon burls into a tree for years. Steals its nutrients and turns its branches into van sized chaotic knots that eventually killed the top of the tree.

That is the summary. Yes, it sounds terrible. Why on earth would our mission today be to convince you the listener? That this isn’t just a pest because to understand the true value of dwarf missile toe, you have to shift your perspective. Okay, let’s shift it. If you only look at the individual tree, especially a heavily infected tree, yes, the missile [00:10:00] toe is harmful.

That specific tree is suffering, right? It’s undeniably bad for that one tree though. It’s worth noting that lightly infected trees show almost no significant impacts. They just carry on. But when you zoom out, the narrative completely flips out.

So these plants are native to Oregon and they are absolute champions of biodiversity. It all comes back to how it spreads. Remember those explosive seeds, They only travel 35 feet. That means missile toe doesn’t spread evenly across a landscape like a blanket. It creates distinct pockets or infection centers, These pockets become very different from the un infested areas of the forest around them.

In ecology, we call this structural heterogeneity. A uniform, perfectly straight forest of identical trees planted in neat rows is a biological desert. The mistletoe breaks up that uniformity. It introduces chaos, and that chaos creates real estate for wildlife.

In the dry forest of the Eastern Cascades and the Klamath Siskiyou region spotted owls actively seek them out. To a spotted owl, a massive van sized Douglas Fir [00:11:00] Witches broom is a mansion.

It provides incredibly dense cover from predators and the perfect stable platform for nesting. It’s incredible. The parasite is basically the forest’s. Eccentric architect building crucial habitat for an iconic, threatened bird species. And it’s not just birds, right? The insect life is heavily tied to this too.

There are two specific butterfly species in Oregon that are entirely dependent on this plant for their survival. On the west side of the state, you have the Johnson’s hair streak butterfly. Over in the dry pine forests, you have the thicket hair streak The caterpillars of both of these butterflies eat only dwarf missile toe aerial shoots. It is their sole food source. If a forest manager were to somehow magically eradicate all the dwarf missile toe, they would wipe out those butterfly populations entirely. The conservation of these insects strictly requires the conservation of the parasite.

The predictions regarding how climate change will affect worth missile toe are complex and they present a fascinating paradox.

climate change isn’t just about [00:12:00] warming. It’s bringing hotter, more severe droughts to these exact regionsand drought stresses trees out immensely. In areas facing prolonged droughts, trees already infested with missile toe are going to suffer increased branch death.

leading to overall forest mortality. This is the crux of the parasites dilemma. Dwarf missile toe is an obligate parasite. It requires a healthy living host to survive and reproduce. It doesn’t want to kill the host,

It wants to milk it for decades. But as trees become deeply stressed by climate change, heat domes, and increased drought, and as severe catastrophic stand replacing fires become more common due to that dry fuel. The host trees simply die, and when the host tree dies, the missile toe instantly dies with it.

So counterintuitively, the extreme stress of climate change may ultimately cause the overall population of this parasite to decline, even as it tries to move north. It is a delicate, chaotic balance. Yeah, and that really brings us full circle on our mission today. We started this deep dive looking [00:13:00] at dwarf missile toe It’s an invasive seed shooting parasite that creates van sized deformities, steals water, and damages valuable timber. But by looking closer at the actual ecology, you realize it is so much more than that. It is a vital native architect of the forest. It creates literal mansions for spotted. It is the exclusive food source for beautiful butterfly species, and it introduces that necessary life-giving complexity into the ecosystem.

I think this deep dive proves something really profound the label of pest is almost always just a matter of human perspective. what we view as a nuisance, a deformation, or a loss of timber the forest often views as an essential building block for life.

It encourages you to look closer at the chaotic, imperfect parts of your local ecosystems and recognize that the chaos usually has a profound purpose. Absolutely. The forest knows exactly what it’s doing, We spent some time talking about the shield effect.

How certain trees, like the Western red cedar are naturally, completely immune to these complex, deeply embedded endophytic [00:14:00] parasites. The SGL seeds just bounce off or quietly die on their branches. Exactly. If biologists can understand exactly how that cedar tree rejects the parasite on a microscopic cellular level.

Could unlocking the biological secrets of that native immunity hold the key to protecting vulnerable agricultural crops around the world from completely unrelated parasitic threats. It’s an incredible avenue to explore. Can the forest teach us how to build better biological shields for the food we eat?

It’s something to think about the next time you look at a tree. Thank you so much for joining us on this deep dive today. we’ll see you next time.

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