|Changing landforms and the movement of continents over millions of years change the habitats available to forests. For example, 70 million years ago, what are now North America's Rocky Mountains had not yet been formed, and that area was covered by a vast sea. This was followed by intense volcanic activity and uplifting of mountains. New land was created, though at the same time, the climate was cooling and becoming more arid.|
|Of course, forests can and do change on much faster time scales as well. Many disturbances can greatly change the composition of a forest extremely quickly, including fires, floods, pollutants, "alien" species and pests, volcanic eruptions, humans.||
The hala tree grows to about 35 feet (10 meters). These trees are over 250 million years old, and one of the world's most ancient plants. Photo by Maya Walters.
|The way in which cleared areas are re-colonized by plants is called ecological succession. Different plants grow in different places, but the patterns of ecological succession are similar all over the world, in both temperate and tropical forests. First the tough, annual grasses move in, followed by shrubs, and finally after several years, trees. The intermediate stages of vegetation are necessary for a new forest to grow, and if an area is disturbed too often, the soil loses too many nutrients and instead of returning to forest, the area remains a grassland.|
[humans & forests] [temperate regions] [tropical regions] [prehistoric forests & amber] [ecological succession] [seasons]
[climate change] [fire] [pollution] [soil] [threats to forests]
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