How birds and plants are moving north to escape the heat

HostIt's strange to think about, but the woods and fields we grew up with aren't actually staying in one place. We usually think of nature as a steady backdrop that stays still, but lately, it's more like a slow motion crowd heading for the exit. I was reading that it's not just one or two kinds of birds, but entire groups of living things shifting toward the poles. What's actually driving this big move?

GuestIt's a bit like a slow motion wave. If you live in a spot where the summer is getting too hot to handle, you have a few choices. You can stay and try to deal with it, you can die out, or you can find a cooler spot. For most living things, that cooler spot is either further north or higher up a mountain. Experts have found that, on average, these groups are trekking toward the poles at a rate of about ten or eleven miles every ten years. It doesn't sound like much, but when you look at how far they have gone since the middle of last century, we're talking about moves that span hundreds of miles. It's a massive, quiet shift of the entire map of life. Every living thing has a sort of comfort zone where the air is just right and the rain falls when it should. As the world warms up, that comfort zone moves, and the plants and animals have to follow it or they simply won't make it.

HostI can wrap my head around a bird flying a few miles north every year to find a better nesting spot. But when we talk about a whole community moving, that includes things like trees and wildflowers. How does a forest march?

GuestThat's a great thing to think about because a tree obviously can't pick up its roots and walk. But a forest moves through its children. Think of it as a generational relay race. A tree on the southern edge of the woods drops its seeds. Those seeds might blow in the wind or get carried by a squirrel. The seeds that land in the hotter, southern side might struggle to grow because the ground is too dry or the air is too warm. But the seeds that get carried a bit further north find that the soil there's now just as warm as their old home used to be. They sprout and thrive. Over decades, the old trees in the south die off and new ones grow in the north. The whole forest creeps forward, one seed at a time. It's slow, but it's steady. The problem we're seeing now is that the heat is moving faster than the trees can drop their seeds and grow. The climate is sprinting, while the forests are just taking a brisk walk.

HostSo the trees are falling behind. But if the birds and the bugs can move fast, does it really matter if the plants are slow? They'll all meet up again eventually, right?

GuestThat's actually where things get really messy. We call it a mismatch. Imagine you're a bird that moves north because the spring is coming earlier and you need to beat the heat. You arrive at your new home, ready to lay eggs. But the caterpillars you usually feed your babies aren't there yet because the plants they eat haven't moved north yet. Or maybe the flowers you rely on for nectar have already bloomed and died because they responded to a different cue in the weather. These groups of living things aren't just a list of names. They're a web. They rely on each other for food, shelter, and even for help spreading seeds. When some members of the group move at sixty miles an hour and others move at one mile an hour, the web starts to tear. You end up with birds in a place where there's no food, or flowers that have no bees to help them make seeds. The whole community starts to break apart.

HostBut isn't there a limit to how far they can go? I mean, we have paved over so much of the world. It's not like there's a clear path of dirt and grass all the way to the arctic.

GuestYou hit on the biggest wall they face. In the past, when the world warmed or cooled naturally, there weren't any highways or giant cities in the way. A forest could creep across a continent over thousands of years. But today, a group of wildflowers moving north might hit a six lane freeway or a massive field of corn that goes on for miles. For a tiny bug or a slow moving plant, that might as well be a brick wall. They get stuck in these little islands of green that are getting hotter and hotter, with nowhere to run. We have built a world of fences and concrete right in the middle of their escape route. It makes the whole journey much more dangerous.

HostSo if they get stuck or if the groups get split up, we're looking at a completely different landscape in a few decades. Is there any way for these communities to stay together, or are we just watching the natural world scramble to survive?

GuestThe big question now is whether we can help these groups stay together by creating green hallways between our cities, or if we're going to end up with a world of lonely species that lost their neighbors along the way.

HostThose woods in the backyard might look the same today, but the maps are being redrawn every single spring.