Natural vegetation grows slowly in barren soil, which makes it difficult for the land to renew itself, and, over tens of millions of years, it repeatedly collapses and is reconstituted, only then becoming a complex, stable forest ecological system.
原生植物在貧瘠的土地上緩慢、艱困地演替，往往歷經千萬年，再三崩解與重建，才成為高度複雜、穩定的森林生態系，也才能擔負土地保全作用。