[ ♪ INTRO ] This episode is sponsored by 80,000 Hours. 80,000 Hours is a nonprofit that aims to help people have a positive impact with their career.

Head to 80000hours.org/scishow to start planning a career that can help solve one of the world’s most pressing problems. Most living things need water, from the smallest single-celled organism to your cat, who always seems to be drinking out of your glass when you’re not looking.

Some living things, though, need less water than others. A lot less. The palo verde tree, for example, does just fine even though it lives in places with very little rainfall.

In fact, this tree thrives where other similar species just wouldn’t have a chance. When the mercury soars and other trees are fanning themselves by the pool, palo verde trees find conditions just right to germinate and grow. The palo verde is found in Mexico and the American southwest, including Texas, Arizona, and New Mexico, down into Central and even South America.

The region is home to multiple iconic succulents, plants adapted to store water in their tissues. Think the Joshua tree and saguaro cactus. In fact, Joshua trees keep so much water in their trunks and branches that in very wet years the weight can actually make them fall over.

But the palo verde is no succulent. It’s a pretty basic-looking deciduous tree, the kind that drop their leaves, like your standard maple or elm. But there are some key differences between palo verde trees and other deciduous trees.

The palo verde’s trunk and stems are bright green, and the leaves are a lot smaller than the leaves of most other deciduous trees. Small leaves help the plant limit the rate of transpiration, that is, how fast they lose water through their leaves. This is partly because as a smaller leaf heats up, it’s able to rapidly transfer the heat back into the air.

Keeping its leaves closer to air temperature means the plant doesn’t have to lose as much water to stay cool. Almost like it doesn’t have to sweat as much. But that’s only part of the story.

Like other deciduous trees, the palo verde tree loses its leaves every year. But unlike most of those other trees, it’s drought deciduous, meaning it drops its leaves when the weather is especially hot and dry. In the American southwest, that’s most of the time.

It takes a lot of resources to maintain all those leaves, so dumping them is good for the tree’s bottom line. Still, there’s that small problem of photosynthesis. You see, in most trees the leaves are the only part of the plant that can do that job.

Without its leaves, the palo verde tree needs an alternative way to perform photosynthesis and make food for itself. That’s where the bright green trunk and stem come in. The trunk and stem are green because they contain chlorophyll, the stuff that leaves use to absorb sunlight.

This is referred to as stem photosynthesis, and it means the tree doesn’t need leaves to produce food. In contrast to other species with photosynthesizing stems, for the palo verde tree, stem photosynthesis is at least as efficient as leaf photosynthesis. And without leaves to provide shade, the sun hits more of the stem, which lets the palo verde convert even more CO2 into food.

But palo verdes have other qualities that help them survive in hard times. Like trichomes, hairlike structures that some researchers think may help the tree both capture water and prevent water loss. And deep roots that can tap into groundwater even when everything above ground is dry.

All of this adds up to a significant advantage for the palo verde tree. It can survive and thrive in places where other trees would die. There are some disadvantages, though.

Palo verde trees have thin bark, which means the cambium, the most actively growing part of the tree, is just below the surface. So when a wildfire passes through, there's not much to protect the tree from the fire. Which also means palo verde trees may be more vulnerable in places where invasive grasses are making it easier for fire to spread.

Understanding the palo verde tree’s vulnerabilities and adaptations could be really important as wildfire becomes more common and our climate continues to warm up. It may even help us understand how to conserve plants in general in a warmer world. And as the global climate crisis continues, we’re going to need people working in jobs that remediate some of its effects, as well as people working on the many other pressing issues that face our generation.

But finding those jobs that have a positive impact on the world can be hard. That’s why 80,000 Hours provides free resources to help you find a fulfilling and high-impact career that does good in the world. 80,000 Hours is a nonprofit that aims to help people have a positive impact with their career. On average, a career lasts 80,000 hours.

That’s a lot of your time, so if you can devote it toward a career that fulfills you and helps others, you’ve hit the jackpot. But it doesn’t have to be a matter of pure luck. 80,000 Hours has a decade of research backing their free decision-making tools and guides. So with their help, you can make educated decisions that lead you to a great new career.

If you’re interested in working toward climate solutions, you might like their article, “Mitigating climate change using effective altruist approaches.” It outlines some of the potentially higher impact careers to counteract effects of climate change. Click our link in the description or go to 80000hours.org/scishow to be sent a free copy of their in-depth career guide. That’s also where you can go to sign up for their newsletter full of updates on their research and job opportunities.

Thank you to 80,000 Hours for supporting this SciShow video and thank you for watching! [ ♪ OUTRO ]