Primary and Secondary Ecological Succession

Primary Succession: When the earth warmed the 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.

Secondary Succession: When an event, like a fire or a hurricane, reduces an already established ecosystem, but the soil remains and succession then follows. This is faster than primary succession because the soil is already present. In the tundra this could occur after a fire or a mudslide.

: At Denali National Park, once-frozen hillsides are unleashing cascades of mud as they thaw