How would you pack for a backpacking trip across the entire planet?

Well, you’d need a hat and some sunscreen for the tropics and deserts, some hiking boots for those forests and mountains, and the puffiest coat you can find for the Arctic.

Oh, and a snorkel for river crossings.

Hmm, this backpacking trip is shaping up to be…heavy.

Because, here’s the thing: Earth isn’t just one environment; it’s many.

It’s made up of different ecological regions, or biomes, where communities of organisms are adapted to specific climate conditions.

So, when we think about climate change, it makes sense to think about it as happening in different ways in all these different environments.

Rather than in one big blobby thing we call The Environment.

And plants are a major part of nearly every single biome.

So, they have a lot to teach us about our whole world — and how it’s changing.

Hi!

I'm Alexis, and this is Crash Course Botany.

Can somebody help me zip this thing up?

[THEME MUSIC] In the last few episodes, we have explored the relationships plants have with each other and their environments.

We started small with one-on-one connections and zoomed out to consider entire ecosystems, where a bunch of different species interact with each other and with non-living stuff.

And now, we’re zoomed all the way out — whoa, wait, not that far!

Okay, that’s better — with biomes, the largest units that ecologists use to describe the plant life of different locations.

Each biome contains multiple ecosystems, and all but the most frigid arctic regions are supported by plants.

There are five main types of biomes —forest, desert, tundra, aquatic, and grassland— but they don’t all fit together perfectly like puzzle pieces.

Their edges are blurry, their classifications aren’t always clear, and there are often ambiguous areas where they transition from one biome to another.

Some ecologists prefer to break down those general categories into as many as twenty more specific ones.

But no matter how many biomes there are, plants have important roles to fill in them.

Like, think about an aquatic —or water-based—biome.

Small fish often use aquatic vegetation, like pondweeds or wild celery, to form habitats where they hide from predators and safely lay their eggs.

And insects and waterbirds rely on the vegetation for food.

Now, plants are producers, meaning they form the base of nearly all the food webs on Earth.

Take the savanna, for example— a transitional biome between forests and grasslands.

Scattered trees, like acacias or baobabs, can feed giraffes and elephants, and grazing mammals like zebras and antelopes eat lots of different grasses.

Then, all of the savanna’s carnivores eat animals that have gotten energy from plants somewhere along the line.

Plants are responsible for supporting a wide array of species, which is crucial to the health and function of each biome.

The more diverse our biomes are, the more security they have against species extinction and threats to their food webs.

This variety of life is called biodiversity.

And on a global scale, plants connect all of these complex biomes through nutrient cycles, or pathways that move nutrients between living organisms and their environment.

They’re effectively recycling important stuff like oxygen, water, carbon, and nitrogen, so it can be used again and again, by all of us.

For example, plants are key players in the global carbon cycle.

Through photosynthesis, they turn energy from the Sun, carbon dioxide from the atmosphere, and water into sugars that power their bodies.

Then, as different lifeforms eat plants and animals, they use that energy to power life’s processes, before releasing CO2 back into the atmosphere — some of which, plants suck back up again.

So this all sounds pretty gucci, if you ask me.

Plants bringing far-flung ecological places together in perfect harmony?

It’s like a Pixar film!

I’m already crying!

But we haven’t touched on a major part of these biomes yet—us.

And we’ve had a habit of …throwing things off.

You’ve probably heard of climate change, which describes major changes in the average conditions on Earth over time — things like temperature, precipitation, and wind patterns.

And you also may have heard that it’s caused by an increase in greenhouse gases like carbon dioxide, methane, and water vapor in the atmosphere.

Now, greenhouse gases are not in themselves a bad thing.

They trap heat from the Sun in the atmosphere, and without them, the planet would be too cold for us —and most other species—to survive.

But, since the Industrial Revolution, we’ve unleashed a boatload of additional carbon dioxide and other greenhouse gases from burning fuel.

And unfortunately, no matter how much photosynthesizing they do, plants won’t be able to absorb all of the CO2 human industry has added.

This has caused global average temperatures to increase rapidly, which has a lot of ripple effects, from ocean warming that causes coral to bleach, to severe weather events that threaten us humans.

More on that in Crash Course Climate & Energy.

So, unsurprisingly, climate change and plants do not get along very well.

Extra carbon dioxide in the atmosphere can potentially make some plants grow better, since the air has more of the raw materials they turn into fuel.

But that doesn’t necessarily increase plants’  access to the other things  they need, like nutrients.

And too much CO2 can thicken plants’ leaves, which actually makes them less efficient at pulling it from the atmosphere.

As the climate changes, plants won’t be able to grow in the same ways and the same places they used to.

Like, while some plants are adapted to dry environments, most need a steady supply of water to stay alive.

But climate change causes more frequent and more severe droughts, which can kill plants at alarming rates.

Like in the tropical rainforest, biodiversity is especially concentrated.

This warm, humid biome has a dense canopy of trees that supports incredibly diverse plant and animal life, including thousands of species of birds and freshwater fishes, and hundreds of species of mammals, reptiles, and amphibians.

But drought is causing these trees to die in large numbers, which has a devastating impact on biodiversity, as do human activities, like clearing out forests to make room for agriculture.

All this tree loss has an even bigger impact because of the role trees play in storing carbon and keeping it out of the atmosphere.

We usually think of forests as carbon sinks, because they absorb more carbon than they release.

But the death of these trees has gotten so severe in the Amazon Rainforest that it’s actually become a carbon source.

It releases more carbon dioxide from decaying organic matter than it absorbs in living trees— the opposite of what it used to do.

Similar effects can occur when, due to rising temperatures, water dries up peat bogs, or layers of ice melt in the tundra.

A warming climate can also throw plants off their usual tight schedule that keeps biomes as a whole running smoothly.

Take the trees of the temperate forest biome.

When the temperature warms up, they know it's time to sprout leaves and bloom, or develop seed cones.

But rising temperatures cause earlier springs, which disrupts other species’ rhythms, too.

Animals might come out of hibernation before their prey does, or give birth before the plants they eat have fully grown, leaving them hungry.

And all this chaos can cause plants to wind up in new biomes where they don’t belong.

Plants in the temperate forest biome are shifting towards the planet’s poles and up the slopes of mountains to seek out cooler climates.

And along the way, they’re disrupting grassland biomes that aren’t used to so many trees.

Then those grasses creep into deserts, where they can act like firekindling— and deserts aren’t accustomed to burning frequently, like some other biomes are.

So, yeah.

It’s rough out there for plants, and biomes, right now.

And reducing carbon dioxide and other greenhouse gases in the atmosphere is a complex challenge.

Like, you might think, “If trees remove so much carbon from the atmosphere, isn’t the obvious solution to plant trees, well, everywhere?” Not exactly.

Because when we consider solutions to climate change, we also need to take into account all of the connection points between and within biomes.

I’ll show you what I mean in the Thought Bubble… In 2021, a French oil and gas company came up with a plan: to help make up for, or offset, their fossil fuel emissions, they were going to plant 40,000 hectares of an Australian tree in the grasslands of the Republic of the Congo.

Now on one hand, that many trees would absorb 10 million tons of CO2 over the next two decades.

Yay!

But on the other hand, it would essentially establish a new dominant species in the ecological community— one that the local plants and animals had not evolved to live with.

Adding so many trees would threaten the ecosystem’s water and nutrient supplies, as the trees suck up resources that native plants and animals also need.

And because trees absorb more heat than grasslands, there’s a risk that temperatures in the area would actually increase, further disrupting the ecosystem.

Another plus of the project is that it would create jobs.

But…there are also concerns about small farmers being displaced from land that the Congolese government allotted for growing trees.

So, while it’s common to hear of companies planting trees to offset their climate impact, the reality is more complicated.

As the old tree-planting adage goes, you’ve got to “plant the right tree, in the right place, for the right reasons.” Thanks, Thought Bubble!

The good news is there are some really amazing actions that ecologists and everyday folks are taking to protect these biomes and their complex ecosystems.

Like, ecologists in Virginia have led one of the most successful marine restoration efforts in history.

They repopulated the state’s coastal bays with 9,000 acres of seagrass meadows that had been destroyed by disease and a hurricane decades before.

Thanks to their planting of eelgrass seeds over the marshy land, the once-barren ecosystem is now flourishing, and the seagrasses are storing a ton of carbon in their root systems to boot.

And across the world in Bhutan, government leaders adopted a constitution in 2008 that protects the nation’s forests.

It mandates that sixty percent of the country remain forest forever.

The carbon-storing powers of its trees, plus the hydroelectric power it generates from its many rivers, made it the first carbon-negative country.

Meaning, it’s kind of like a country-wide carbon sink, storing more carbon than it releases.

So, yes, touring the world’s biomes in an era of climate change is bound to reveal challenges.

But it also reveals the intricate web of connections that make life work.

And plants?

They fuel it, provide shelter in it, and connect each living thing to each other, including us.

So, however much you packed —or overpacked— we’re all along for this ride.

Next time, we’ll be looking to the future of botany, from the global problems plants could help solve,