When people think about the Arctic, what often comes to mind is treeless, windswept tundra. And there's certainly a lot of treeless, windswept tundra in the Arctic, but there's also a lot of trees. Now, the word tundra basically means treeless plain. And the location of tundra, or the latitude in which we find tundra, is really largely determined by summer warmth. Rule of thumb is if the July average temperatures are greater than 10 degrees C, you can have trees. If the July average temperatures are less than 10 degrees C, it's really hard for trees to grow, and you have tundra. Now, some tundra areas in the Arctic are what we call polar desert, very dry, and not a lot of vegetation is actually there. Some areas are much more lush. And generally tundra gets shrubbier as we move toward the southern limit of tundra. Now, there usually is no sharp treeline, I mentioned this 10 degree July C isotherm, okay? But that's just kind of a rule of thumb. Because in reality, there's really no sharp treeline. It's an ecotone or a transition zone between tundra to the north and the boreal forest that lies to the south. This image that I'm showing indicates the areas in the Arctic where there is tundra. Anywhere with this coloring there is where we find tundra. Now, there's many different types of colors there. And what these are simply showing is that there's many different types of tundra. Tundra isn't just this one thing, there's a number of different varieties of tundra, polar desert tundra being basically one of them. This picture here is showing one rendition of where polar desert areas are located. The areas in the dark shading are, by this rendition, where we will find a polar desert. And you will see polar desert, we find it throughout the Canadian Arctic archipelago. We find it over parts of coastal Greenland on the north. On the Russian side, we find it over Novaya Zemlya, of some other areas as well. But that dark line is also showing the rough location of the treeline. And so you can see we can find areas of trees actually well, well north of the Arctic Circle. And as it turns out, there's areas actually of tundra, not shown here, which actually extend even south of the Arctic Circle. So these rules of thumb are just that, there's rules of thumb, there's a lot of exceptions. Now, the picture I'm just showing now is one that someone took of me back in 1982, I think it was, where I am standing on a polar desert area on northern Ellesmere Island. This would have been in July sometime, the snow had melted. And as you can see, it's a pretty severe terrain here, there's not much of vegetation growing there at all. This next picture is showing another area of polar desert, fairly near the first one. And you can see there's not a lot of vegetation. You see those hummocks, those are actually permafrost features where you get that hummocky ground forming in these kind of areas. kind of hard to walk around sometimes if those hummocks get big. But this is pretty classic of polar desert areas. Now, here's a question. Polar deserts, of course, implies that there's low precipitation. But let's ask, why is precipitation so low? Well, there's two parts to it, two answers. Number one, the areas are far from moisture sources. Now, you might say, well, isn't the Arctic Ocean a moisture source? Actually it doesn't give you much moisture. Because, remember, it's mostly ice covered, even in summer. And basically it acts as a lid and it separates the Arctic Ocean, which would be a moisture source, from the atmosphere above. So yeah, pretty far from moisture sources. But also, the Arctic is cold. And this is important because the Arctic air will not hold much water vapor. The amount of water vapor the atmosphere can hold depends on the temperature. The higher the temperature, the more water vapor the atmosphere can hold. So the Arctic is cold, can't hold much water vapor, far from moisture sources. Put those things together, it's hard to get a lot of precipitation. So it's really both A and B is the answer here. Now, some areas of tundra are much more lush. This is what's called a maritime tundra area. This is a shot I took from a Svalbard some years ago. That choo-choo train there is a little train that was used to service the coal mines, there's coal mines in that area. And you look at the surface there and how lush that tundra looks compared to the polar desert area. This is all relative, of course. Some people would say, my God, there's not much going on there in terms of vegetation. But I look at that and I say, that's a nice lush maritime tundra area. Now, some parts of the Arctic, especially on the southern ends of the tundra, that tundra is much more lush and it's actually rather shrubby. So here you see a scientist walking through some of this shrubby tundra area in the Alaska area, I believe this is, nearing what we call the Bering land bridge area. So a lot of willow and things like that, so very, very different types of a tundra. You can see the Arctic Ocean up there near the top of the image. Now, as I mentioned, this treeline that we see is not distinct. It's really a tundra forest ecotone, it really a transition, and ecotone meaning a transition. Now, it's called a tundra-forest ecotone. Some people call it a tundra-taiga or a taiga-tundra ecotone, really two words for the same thing. In North America, that transition is usually made of black spruce or some white spruce, whereas in Eurasia, it's mostly larch. Now, the boreal forest, also termed the taiga biome, is found to the south of that ecotone, that transition zone. What I'm showing here is a picture of the taiga south of Inuvik in the Northwest Territories, beautiful picture, I think. What you see is lots of wild flowers. And then in the back, you see some trees, it's probably mostly black spruce, it may be some white spruce in there at all. But it's typical of what you see, it's patchy. There's some areas of tundra, some areas of trees. And as we move north, you get fewer and fewer trees, until you really transition very much into just a tundra, tundra landscape. Now, people have tried to map this ecotone or transition zone, and this is one such analysis for North America. There's two classes in here. The one in the red is where there's provide the 20% tree cover, what they're calling canopy cover. And they're calling it Class 2 to the north, where there's less than 5% tree cover. And that's in these blues and the Class 1 is in the reds. Just a simple point to be made here is that the transition from the boreal forest ,which is shown in the green to the south, to the tundra, which lies north of that ecotone, is just not distinct at all, right? It's very varied, and it's a gradual transition. Generally it's not an arrow transition, there are some exceptions, but generally it's a fairly wide zone. This is the same type of analysis done for Eurasia. And you see the same thing, it's the same sort of analysis. And we see that the boreal forest just slowly peers out as we move north, until we get into a tundra environment. So again, that idea of a 10 degree July isotherm north of that, no trees, south of that we have trees, it's just a rule of thumb. It's a very, very sort of rough estimate because a lot of other factors are involved. This last a picture I'm showing here is the same analysis, but for the Alaska area. And this is one area where this idea that that treeline is kind of non-distinct doesn't hold. What's happening here is you move up into the Brooks Range and get to the north of the Brooks Range, suddenly the trees stop. The Brooks Range is a barrier. As in the south end of the Brooks Range, as we move into it from the south, we get into higher elevation, so it gets colder by that factor. As soon as we cross the Brooks Range, we're into a tundra environment. Now, a part of that is the Brooks Range acts as kind of a topographic barrier. It traps the cold Arctic air and keeps it from going south of the Brooks Range. So it kind of traps that cold air to the north, and it's too cold for the trees to grow. So in the Brooks Range, that's where you really see a pretty sharp transition as you get over the path right into the North Slope. There used to be a sign on a tree, I recall this, some years ago that said something like, this is the northernmost tree in Alaska. I'm not sure whatever happened to it. Point is, actually, in a lot of areas in the Arctic, the treeline is actually slowly advancing a poleward as the climate warms. So there's a lot going on over the Arctic lands in terms of tundra versus trees. It's generally not a sharp transition. There is this tundra-taiga ecotone. So again, another fascinating aspect of the Arctic environment. Thank you.