About 10, 000 years ago the area known today as the temperate forest was covered with glaciers. When the earth warmed those glaciers retreated and left behind land that was lifeless and rocky. It took a very long time before pioneer plants like lichen started to grow on these rocks. In time, rocks broken down by the lichens mixed with decaying lichens and formed the first soil. Wind also blew dust, which congregated in small cracks in rocks where moss and small plants started to grow. Like lichens, moss obtains water by absorbing moisture in the air. Soon, more moss and more soil forms. Decaying moss mixes with rock chips and dust to form more soil. Because of this, grass begins to grow in the area. As soil becomes more plentiful, more and more plants begin to grow. These stages of soil and plant sophistication are called primary succession. Through this process the temperate forest was formed.
After grasses and more plants grow in the area, small animals, birds, and insects start to make the land their home. Soon winds bring seeds of more complex plants to the area. Larger trees like pines, aspen, and birch begin to grow and dominate what was once just a grassy field. Bigger animals visit the land and soon make it their home. At this point, simple plants like the lichen cannot compare with such large trees. In the shade of the trees they continue to live, but do not thrive as they once did. After shade develops from the first large trees other types of trees begin to grow in the area. What has now formed is called a broad-leaf forest. This young forests life continues to grow into what is called a climax forest.
The pines, aspens, and birches have grown too rapidly and, now, sun for their saplings to grow has been shut out. New trees cannot grow in this shade. As a result, the forests under story started growing shade tolerant oak, tulip trees, beech, maple, ash, hemlock, and many other types of trees. Slowly, the pines, aspens, and birches died out. This is now the middle stage of succession.When the pines, aspens, and birches completely die out these newly formed trees shoot up and dominate the forest. At this point the forest has reached its climax stage. Climax forests are different depending on region, but are notably very stable and can survive for thousands of years.
No matter how devastated a land may be, in time it will always return to a forest. No glacier, volcano, landslide, or clear cut can prevent this. This process is called secondary succession. Secondary succession generally occurs much quicker than primary succession, because, in most cases, soil has already formed. Soil formation is the longest process in primary succession. The only occasion where a climax forest cannot grow back is when forests are cleared for cities or farms. In these events the top soil is ruined and it will likely take thousands of years before the soil is rich enough for a climax forest to grow in that area. Other climax communities, including the temperate forest and its four varieties, are the land biomes: tundra, taiga, grassland, desert, chaparral, and tropical rain forest.
Fire, often caused by lightning, is one way that temperate evergreen forests remain dominant in their region. This is because many species of conifer trees, like pines, are nearly fire resistant. Sometimes trees that are less fire resistant, like deciduous trees, invade evergreen forests. The deciduous trees will dominate the forest unless a fire stops them. These trees will die in the fire, while the fire resistant trees will still stand tall. Fires even promote evergreen forests to grow. Fires speed up the decomposition process of needles on the forest floor, which then releases nutrients into the soil. Heat from the fires burst open seed cones and scatters them on the newly enriched soil. This natural process promotes growth of evergreens.
Fires do not maintain the other temperate forests like they do for the temperate evergreen forests. Typically deciduous forests and temperate rain forests are too moist for fires to start. However, if a drought occurs in one of these regions a fire can become a possibility. Fires in these forests, and even in mixed forests of conifers and deciduous trees, can be devastating. The natural process of succession is the only way a new forest can once again dominate the land.