 You are clear for launch. And with that, shut down your visors, O2 on, and prepare for ignition to O2. You can copy that and, um... Hey, it's Mr. Ruchoff again. All right. In our last two lessons, we discovered how the Sun and the Earth's relationship, as well as five factors, combined to be able to create the world's climates. In this lesson, what we're going to do is we're going to look at the Earth's biomes. And what is a biome? Well, biomes describe the ecosystem of an area that is tied to the different climates. And is the temperature and the precipitation that each region receives that actually is going to determine the flora and the fauna of these different regions. Now, flora is the plants and trees that are found in the area, and fauna are the animals that are found in the area. Now, while it's fascinating to discuss how the biome supports different sites of fauna, due to time in this lesson, we're going to limit our discussion on the type of vegetation or the flora that each biome supports. Now, there are several broad groups of biomes. There is forest, grassland, desert, tundra, freshwater, and even marine biomes. Now, the freshwater and the marine biomes refer to the vegetation of animals that live either in freshwater areas such as lakes and ponds or in our oceans. And as interesting as these are, we're going to spend our time on the four land-based biomes of the forest, grassland, desert, and tundra. Now, forests cover nearly a third of the Earth's surface, and some 300 million people live in the forest, but it's certainly not just people that live in the forest. It is estimated that 80% of the Earth's biodiversity is actually found in these forests. But there are many different types of forests. We can describe them in many different ways. First, we can divide forests by the type of leaves that the trees have. There are something known as broadleaf trees, and these are the trees with flat leaves like an oak or maple tree. Needle leaf trees, also known as conifers, have needle-type trees, much like what you find on a pine tree or a Christmas tree. Now, if a forest has both broadleaf trees and needle-leaf trees, they are often called mixed forests. Now, we can also divide forests by whether their trees lose their leaves seasonally or not. Now, forests that lose their leaves seasonally, we're talking about those trees that turn those beautiful reds and yellows before they actually have their leaves dropped to the ground. These are called deciduous trees, and those trees that do not have this seasonal shedding of their leaves are called evergreen trees. Now, evergreen trees can also be called conifers trees or the conifers or the needle-leaf trees. Pine trees will drop their needles, but they will drop them throughout the year and not at one given time. But evergreen trees can also refer to broadleaf trees in warm climates that remain green all year long and only shed their leaves due to age. And we usually will find these in the low or the tropical latitudes. Now, speaking of latitude, we can also divide forests by where they are in relation to the equator. Specifically, we have tropical temperate and we have boreal forests. And as you can guess, tropical forests are in the tropics within 30 degrees of the equator. Now, in the tropics, the most common type of forest is the tropical rainforest which is found in areas in the tropics that have a great amount of precipitation throughout the year. The Amazon rainforest in South America or the Congo rainforest in Africa are great examples of tropical rainforests. Now, tropical rainforests are nearly exclusively made up of these evergreen broadleaf forests that support the world's most diverse ecosystem. In fact, in a tropical rainforest, in just four square miles, you can find literally thousands of different species of plants, birds, insects, and other animals. Now, these different species of trees will create different layers of canopies that will block most of the sunlight from actually getting to the ground. Essentially, a tree canopy consists of the leaves and branches that actually provide the shade below. This is kind of like an umbrella leaves. The tallest tree creates what is called an emergent layer. With trees as tall as 200 feet, this layer is going to receive the most daylight. Below the emergent layer is something called the canopy layer because it is the primary layer of the forest. The canopy layer will also receive a great deal of sunlight that isn't blocked by the emergent layer. Now, below the canopy layer is the understary layer. Now, by this point, the two upper layers of the emergent layer and the canopy layer has blocked most of the sunlight. So, these trees in the understory will give us larger leaves to be able to absorb what little sunlight is available. Then there is the floor of the Tropic Rain Force. It is actually quite dark on the floor. In fact, when I was doing training in Panama, I was amazed at how dark it actually was. I would describe it as being about as dark as a room, but the light turned out and this shade pulled. And at night, it is absolutely pitch black as none of the star or the moonlight actually ever gets down to the ground. Now, because all of this lack of light reaching the floor instead of having a thick underbrush, the floor of the Tropic Rain Force is largely barren of any type of vegetation because there just isn't enough light to be able to support that type of plant life. The exception is when you're near a road or a river. And Panama took my unit nearly an hour to move out of the last 100 meters of Tropic Rain Force to get to the road that was running right next to it. Now, what is surprising is that despite supporting so much vegetation, the soil of the Tropic Rain Force is actually quite poor in nutrients. This is because the large amount of rain that these areas receive actually washes the nutrients from the soil. Now, fortunately in a Tropic Rain Force, the organic material decays much faster than other regions so the vast amount of vegetation that falls to the ground decays and keeps the ground fertile enough to be able to support the ecosystem. Now, as we move into the middle of latitudes, we begin seeing needle leaf trees in addition to our broadleaf trees. Broadleaf trees are also more likely to be deciduous or trees who leaves turn color and drop to the ground in the fall. Latitude and elevation plays a large part in deciding when these trees will turn their colors. This process will begin earlier as the temperature is cooler and latitudes further from the equator and areas that are higher up in the mountains. Now, because of the canopies of these broadleaf, coniferous, mixed forests and temperate latitudes are not as thick as the Tropic Rain Force, you're going to find that the underbrush in these forests are much, much thicker. Now, in the middle latitudes, we do find Rain Force, temperate Rain Force. We find these in the cooler areas where there's lots of precipitation. Temperate Rain Force do differ from Rain Force, though in several different ways. First of all, temperate Rain Force can have both broadleaf and coniferous trees, although typically your coniferous trees, such as your woodwoods and your spruces will dominate in these forests. And while temperate Rain Force will have dense canopies, they're not as diverse as their tropical canoparts. Temperate Forest will only have about three or four different species per square kilometer, as opposed to the hundreds of different species per kilometer that we'll find in a tropical Rain Force. Now, as you move between 50 and 60 degrees latitude, we start seeing our Boreal Forest. Boreal Forest, also known as Tiagas Forest, are made up of coniferous trees specially adapted to be able to survive the brutal winters of that latitude. A perfect example of a Boreal Forest is found in Canada and in Russia's Siberian Plain. Now, while forests cover nearly a third of the Earth's land area, nearly 40% of the land area is covered by grasslands. And from their name, we realize that grasslands are areas that are dominated by, well, grasses. But these grasslands are incredibly important because most of the world's agriculture comes from grasslands. In fact, 70% of the world's agricultural lands actually are grasslands. And just like forests, there are several different types of grasslands. When we look at the low latitudes or the tropics, we find a savanna in those areas that have a wet season and a dry season. Now, unlike a tropical rainforest, a savanna doesn't receive a large amount of rainfall all throughout the year. So there isn't enough precipitation to support large forests. Instead, we have a grassland with scattered trees. If you think of where zebras and drafts live, you're thinking about a savanna such as these pictures I took when I was in Tanzania. As we move into the middle latitudes, we get temperate grasslands, in which grasses dominate the vegetation. We get trees, but usually we're going to find these trees along river valleys where there is a constant supply of water. The type of grasslands largely differ based upon the amount of precipitation that each receives. Grasslands with more precipitation will tend to have taller species of grasses. As precipitation reduces, you'll begin to get shorter grass species until you get to something called a step. A step is the type of shortgrass grassland that is found in regions that receive no more than 20 inches of precipitation throughout the year. The American Great Plains that stretches from northern Texas all the way up through Kansas and into Canada is actually a step. We also find steps in Central Asia where continuity has reduced the amount of precipitation that a region receives. Then we have something called a chaparral. Technically, a chaparral isn't a grassland biome nor is it a forest biome. And while there may be some short grasses and even some trees such as evergreen oaks, this biome is dominated by shrubs and brushes such as sagebrush. The chaparral biome exists in areas typically that receive between 10 and 17 inches of rain each year, but most of that rain comes in a short winter season. This means that for most of the year the chaparral doesn't get any rain at all. So the animals and vegetation in the chaparral have evolved to exist in these long, dry periods throughout the year. For example, the shrubs and brushes of the chaparral have thick, waxy leaves that allow shrubs to be able to retain their moisture. They also have large root systems that allow them to take advantage of the scarce water that is in the soil. While the steppe and chaparral biomes are in dry areas, the real dry biomes are the deserts, which cover 20% of the Earth's surface and regions that receive less than 10 inches of rain each year. Now, semi-arid deserts can receive up to 20 inches of rain each year, much like our steppe and our chaparral climates. But the semi-arid deserts will be in areas where the evaporation and transpiration of water and moisture from the soil and plants due to temperature, humidity, and all characteristics of the region. Now, vegetation in deserts is rare, and sand actually covers one-fifth of the deserts of the world. Now, we usually think of cacti when we think of desert vegetation, that there are other plants. These are usually plants that are low, hugging the ground, and have long tap roots to be able to reach the water below. Our last major biome category is the tundra, which is the coldest of all biomes. And we have arctic and alpine tundras. Arctic tundras are found in high-latitude areas, and alpine tundras are found in high-elevation areas up in the mountains. In both of these tundras, the temperatures are best cool in the summers and brutally cold in the winters. In fact, so cold you're not going to find trees in the tundra. In fact, the word tundra actually comes from a Finnish word that literally means treeless plain. Now, vegetation in the tundra is largely limited due to low shrubs, mosses, liverworts, flowers, and short grasses. Now, one unique feature found in the arctic tundra is something called permafrost. Permafrost is a layer of permanently frozen subsoil. And I'll ask you if the permafrost could be up to 740 meters thick, but not to be outdone, the permafrost in Russia's Siberia is over twice as thick at 1,500 meters. Now, when we examine life in Russia later in this course, we're going to see how this permafrost creates problems through constructing buildings and how people have adapted to being able to build on it. So those are the biomes which are created by the temperature, the precipitation patterns of the Earth. In our next lesson, we'll look at another way in which we can classify the climates by the Earth by something known as the Copen climate system. But until then, keep on learning.