World Builders™
World Builders™
Session Eight --  Land Plants  
Session Eight  -- Land Plants  

Life Returns to the Landscape
Life Returns to the Landscape


How long does it take for plants to return to land covered by molten lava?

dead tree

 After a volcanic eruption, the rock cools to form a lifeless jumble of jagged stones and cinders. The intense heat has destroyed all living organisms, even seeds and spores. It takes time for life to begin again in these places.

     The ash and cinders that were blown out of the volcano contain minerals that plants can use. Cinders and ash are small bits of stone, and rain water pours down through them until it hits a rock layer in the ground below. Although this jumble of small rock particles can make water available for roots, it also allows the water to keep on draining down, leaving the roots in dry stones again after only a few minutes. It may have excellent drainage, but poor water-holding capacity.

     Soil is not made of minerals alone. It contains little bits of organic material that are being broken down by decomposers. Decomposers are living organisms such as bacteria, fungi, tiny nematode worms, and other organisms that may be too small for us to even see. They digest dead stems and leaves, and the bones, feathers and flesh of dead animals. They recycle the nutrients so that they may be used again.  Soils are living communities of organisms, and they take time to develop after volcanic eruptions.

Plant Succession

    After a volcanic eruption, or even a forest fire, plants re-establish themselves in stages. The plants in each stage form a community and make the environment more hospitable for other plants. Over centuries these plant communities succeed one another until a climax community is reached. The climax community may continue for a long time without striking stages until an environmental change creates opportunities for different organisms.

    On cold lava flows, lichens are among the first pioneers. They can live without soil, clinging directly to the rocks. They begin to break the rocks down. They grow slowly, and just dry out and wait if there is no rain.

     Meanwhile, the wind blows dust and sand into the cracks between the stones. Very slowly, tiny pockets of soil begin to form. Wind blown seeds fall into these cracks, germinate, and begin the long process of making a garden out of the volcanic wasteland.

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© 1996,1997, 1998, 1999, 2000, 2002, 2003.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at .