Once the humus layer disappears, nutrients cannot be recycled and leach from the soil, converting soil from fertile to infertile and making it suitable only for savanna vegetation.
一旦腐殖质层消失，养分就无法从土壤中回收和过滤，致使土壤由肥沃变为贫瘠，只适于热带草原植被的生长。
2
Burning the forest just once can leave behind enough black carbon to keep the soil fertile for thousands of years.
森林仅仅燃烧一次就能留下足够的黑碳，来保持数千年土壤肥沃。
3
Land that was once at the bottom of the sea now lies around the town in wide, fertile fields; where crabs once crawled, donkeys pick their way.