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When you picture a tree, you might imagine a tall sturdy pine or a reliable apple tree. Something that produces flowers, fruit or seeds every year for dozens of years. And most trees are like that, but the opposite kind of trees exist as well.

Much like many salmon species do in the animal world, these trees reach reproductive age, release their seeds in a single massive burst, and then promptly die. And these aren't short-lived trees either, we're talking plants that grow for decades before fruiting once, and then kicking the bucket.

It's hard to imagine how this strategy could help your species survive, especially when all the trees around you are putting out seeds year after year. But there is a good reason it works, especially for one species of rainforest tree.

If you're an animal like a salmon, this strategy of having one big reproductive event before dying is called (?)semelparity, but if you are a plant it's called monocarpy. 

Monocarpy is more common in short-lived plants, especially ones that live in environments where growing conditions are poor or can dramatically shift, like bogs, deserts or alpine environments. And that makes sense. These adult plants have to take advantage of a narrow window of ideal conditions. especially if they are not likely to survive until the environment is friendly again. Meanwhile, where conditions are stable, you'll rarely find (?)monocarpic plants. And it's even more unusual for a long-lived tree to put all of its eggs in one basket. Or I guess, it's seeds into one fruiting?

Putting all that energy towards growing into a big, woody tree and then dying after one fruiting kinda seems counterproductive. So these stable environments tend to have polycarpic plants or ones that continually flower.

Except the rainforests of south and Central America are home to a handful of monocarpic trees and one of them is doing incredibly well. It's called Tachigali Vasquezii and it's so successful it might be the 10th most common tree species in the Amazon rainforest of Northern Bolivia. 

In a 2005 paper, researchers tested how these trees were so plentiful despite reproducing just once. And they had a handful of hypotheses to investigate. For instance, previous studies had suggested that monocarpic in the genus Takagali could be an extreme version of masting. Where trees produce extra fruit to overwhelm their predators.

Predators can only eat so much before they have to stop gorging themselves. So by producing way too many fruits and seeds, the tree would ensure that there are some survivors left to start their life cycle again.

In fact, you can view monocarpi as masting turned up to 11. every tree flowers and produces fruit at the same time and then they die. Except when researchers looked at related masting tree species in Panama, they noticed that this strategy didn't seem to make as big a difference as suspected.

(02:40) Insects and other animals still ended up eating the majority of the seeds, even when released en masse. Also although T. vasquezii does release about twice as many seeds as the average Polycarp, its behaviour doesn't look like masting.

If this species was trying to overwhelm predators, you'd expect to see all the T.vasquezii in the forest go a long time without reproducing until suddenly, boom, they release all their seeds at once. Kind of like how periodical cicadas don't hatch for years until suddenly, every tree in your neighbourhood is full of screaming insects. 

But that's not what happens here, so another hypothesis was that trees in the genus Takagali might be so plentiful because they have better survival rates as juveniles and this seemed true, at least at first.

(03:20) The recently germinated seedlings did have a higher survival rate than similar species, specifically species whose seeds are spread by the wind. But it didn't stay this way.

Once they got a little bigger, T. vasquezii's saplings ended up dropping off, and their survival rates ended up worse than those of polycarps. So there goes that hypothesis.

(03:42) Meanwhile, other researchers studying other trees in the genus thought that maybe its the gap in the canopy left by the dead tree that led to T. vasquezii's success. They hypothesized that the adult trees died to give their offspring more access to sunlight, so that they are not forced to live in their parent's literal shadow. 

(03: 59) and while juveniles of T. vasquezii do typically occur in bright conditions more often than other tree species found around them, this doesn't explain their success. 

That's because like we mentioned earlier, T. vasquezii seeds are spread by wind. So, not a lot of them fall directly below their parent anyway. Whether or not there is a gap in the canopy there doesn't matter as much. 

So, this isn't the whole story. And that brings us to a final hypothesis. 

(04:24) This last idea was that there are so many T. vasquezii trees because they just grow faster. The thinking was that this tree can put all of its energy into growth until it reproduces. Other trees have to devote a ton of resources into reproduction every year, so they don't grow as quickly. 

And- ding, ding, ding! This was the winner!

(04:42) The researchers learned that this tree can grow fast, with its diameter expanding about four times faster than its polycarp neighbors. And much like the contractor who built some of my previous apartments, this tree does this by cheaping out on construction material. Instead of putting energy into making dense wood, it produces a lot of lightweight wood and a big leafy crown to capture sunlight. As a result, it reaches reproductive maturity in only 49 years. Which sounds like a super long time, but its shaving about 30 years off the average polycarp reproductive age in these forests. 

This strategy also means more individual trees will reach this stage, because they don't have to survive as long as others. So in the end, more of these plants get to reproduce, and the next thing you know, they're one of the most common species in this rainforest. 

Like the salmon that pull off an incredible journey to reach their spawning ground after years at sea, these trees put everything they've got into reproduction. 


They spend decades growing into towering heights, surviving everything from weather to pests along the way, and in the end, it all culminates in one dramatic event: releasing their seeds.

(05:46) But even though T. vasquezii dies in this process, their adaptations allow them to carve out their own niche. Even when surrounded by trees that pump out seeds year after year. 

Thanks for watching this episode of Sci Show. If you like intricate discussions of rainforests, salmon trees - and you probably do because you're here- consider supporting us on Patreon. Your generous support makes it possible for these videos to go up week after week, so thank you. You can get started at patreon.com/scishow. 

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