The lands where flowed lava or pyroclastic flow or fell down other volcanic product because of volcanic eruption become wasteland. However, anyway, the plants begin to grow up and form forests and animals start to live in there. Of course, there are many spots which have the vestige of volcanic damage such as Onioshidashi-en at the Mt.Asama.
　 Let’s think here. After the menace of 1000℃ lava flow and so on, you can imagine there is a few organism which can be alive on the wasteland easily. The limited plants are usually called “pioneer plants.” Don’t you think it’s mysterious that the vegetation can restore. The seeds might be able to come wind and worms, but you may have questions how the plants can secure the nutrition. What is the nutrition which is in the wasteland.

Azotobacter（Image）

　It is azotobacter that solves the nutrition problem on the volcano.

Feature

• absorb nitrogen
• co-exist on the root of plants and cyanobacteria
• they supply nitrogen with plants under the existence of nitrate bacteria because plants need nitrogen when they produce nucleic acid or protein
• co-existed azotobacter can do nitrogen fixation further efficient than the situation it exists alone
• he plants which have azotobacters can absorb nitrogen from the atmosphere though the original plants be only able to absorb nitrogen which melted in the water in the soil
• co-existed azotobacter can do100 times nitrogen fixation as much as other types of nitrogen fixation

Cycad

　Pioneer plants usually have light and tiny seeds to do wind dispersa

• Lichin
• Azolla
• Cycas revolta
• Alnus
• Ceanothus
• Myrica
• Cercocarpus
• Purshia tridentata
• Rhizosolenia
• Miscanthus condensatus

Soils (Lava)

　I wrote the soils formed by volcanic products are wasteland before, but in fact, the lava include phosphorus, potassium, calcium, magnesium, so the essential minerals except for nitrogen are already included in the soil.
　Thus, if the plants can get nitrogen, they can get the minimum prerequisite. Furthermore, as nitrogen fixation proceeds and becomes clay after weathering, phosphorus is caught by clays, so it is said that phosphorus lacks first during the soil restoration. The accumulation of nitrogen as ammonium ion by the pioneer plants enable for original plants to grow up there. That is so happy thing for original plants which can’t absorb nitrogen from the atmosphere. Also, fungi resolutes dead leaves and dead body, which cause wasteland to soils. Thus the cycle toward restoration begins to round.

　pioneer plants⇒annual plants⇒perennial plants⇒intolerant trees⇒tolerant trees
During the transition, pioneer plants are gotten rid of by new-faced plants.
　As proceeding transition and the size of the forests become huge, intolerant trees –they can live with little sunlight- begin to occupy the forests. The matter is not how much it does nitrogen fixation, but how it produces with little sunlight which came through among high trees. The situation is usually called climax and it is the end of the transition in "one meaning"
　What does “one meaning” means? In fact, there is continuation of the transition. Simply put, the forests declines. High trees gradually disappear and the dense of trees become so lower. It is a conclusion from the Hawaii volcanic line –it is formed by hot spot under the center of the Pacific Ocean. Below 10000 years after the volcanic eruption, it goes through its peak and starts to decline. The main two reasons are…

1. aging of soils : lava’s abundant nutrition especially phosphorus lacks because it’s caught by clays.
2. isolaton of an ecosystem : Japanese volcano such as Miyake-jima barely keep its ecosystem by yellow sand, but in the case of Hawaii, it can only get a little sand from Iraq. It means vegetation can’t renew itself and it makes a bad influence on development of vegetation

　The speed of vegetation transition isn’t the same among all volcanoes. It differs from various factors.

1. By the shapes of volcanoes : the shapes of volcanoes depend on property of magma. Especially, the amount of SiO2 is the key to decide formation of volcanic product. Generally, scoria or pumice are faster to restore vegetation than hard lava or always flowing place such as Kilauea.
2. By the climate : climate, especially rainfall and temperature is important. Humid and high temperature places are quick to restore. Low latitudes areas are tend to be such condition. Iwate-san where I went to before was very slower than Miharayama or Sakurajima. Though it has been over 200 years after lava flow, there were Lichin and pines – they are pioneers – a few.
   
3. By the height : basically, the lower the height is, the quicker transition droceeds.

　Transition of volcanic vegetation is important means for us to learn how to use land or how much the soil restored, so many researches not only in Japan but also overseas are studying about the vegetation.