However, local people have indigenous knowledge about their environment.
They know what will grow and what will not grow.
Many people in upland areas use swidden farming.
They clear a piece of forest, burn the vegetation and then plant crops for a few years.
Swidden farming is also called ‘slash-and-burn’ or ‘shifting cultivation’.
This type of farming was once common in all areas.
Now, it is found mainly in the uplands.
Most of the nutrients in a tropical forest are stored in the living vegetation, not in the soil.
Burning the vegetation releases the majority of these nutrients into the soil.
The fire kills weeds, pests and diseases.
The ash improves the soil structure.
The yields in the first year or two are good.
But soon, the nutrients are used up or washed away.
After a few years of farming, the soil is exhausted, and pests and weeds threaten the crops.
Traditional farmers leave the land fallow - to rest for a while and recover.
It takes several years for the soil to recover so the land can again be cleared for crops.