Biol 上遇到一些問題.....The ecosystem

1)Explain why the removal of trees may lead to serious soil erosion.
2)A scientist suggested that the farmers should grow some leguminous plants
along the edge of the field.At the end of the year,the fruits of these plants
were harvested. The leaves and roots were ploughed into the field.
i)State two uses of the fruits.
ii)Explain how the soil fertility can be increased by growing leguminous plants and returning their leaves and roots into the field.