This is the 3249th most frequent Japanese word.
富ん
"富ん" (とん) means "to be rich" or "to be abundant."
Here, the word '富んだ' (tonda) modifies '知識' (chishiki - knowledge), meaning 'rich in,' reflecting a qualitative abundance in knowledge.
彼は富んだ知識を持っています。
He possesses abundant knowledge.
The phrase '自然に富んで' describes the land as being full of natural resources or beauty.
その土地は自然に富んでいます。
That land is rich in nature.
'文化的な要素に富んでいた' uses '富んで' to indicate that the story contains an abundance of cultural aspects.