Lupine

One of the most important plants on Mount St. Helens, is the prairie lupine (Lupinus lepidus), this was the first plant to appear on the desolate pumice plain and is very important to the regeneration of life on Mt. St. Helens. Appearing on the pumice plain in 1982, the lupines are now growing rapidly and spreading through the ash and pumice filled landscape around Mt. St. Helens. The lupine plants share a special interaction with nitrogen fixing bacteria (see Nitrogen Cycle) these bacteria add vital nitrogen to the soil and the decaying plants add organic carbon (see Carbon Cycle). The combination of these two essential nutrients to the pumice plain is creating new soil. A result of this soil formation is the growth of many more diverse species of plants, which are unable to produce their own nitrogen.

According to John Bishop a biologist who has studied Lupinus lepidus for ten years, the impact of the lupine plants has only been important in very small areas. The question which professor Bishop had, was why were the lupines not spreading as rapidly as scientist thought they would. Bishop found that the lupine plants were spreading less rapidly than expected because they were being damaged by lupine loving butterfly and moth caterpillars at the edges of their colonies. The edge regions of colonies are thought to be very important in the dispersal of seeds into new areas, thus allowing the colony to grow. Bishop does not currently know why the insects are only damaging the edge plants of the lupine colonies, and not the interior areas. The leading theory is that the plants at the edges of the colony are of a better quality than those in the center of the colony, thus making them more desirable to insects.