Complex sentence: Väinämöinen summons Sampsa Pellervoinen (the architect of the forests) to sow the land with trees, he sows many trees and in time they grow and flourish, however the oak will not grow.
Split into simpler sentences: Väinämöinen summons Sampsa Pellervoinen (the architect of the forests) to sow the land with trees. He sows many trees and in time they grow and flourish; however, the oak will not grow.