Complex sentence: For the natives the Pine Bush was an important source of firewood and animal pelts to trade with the Dutch, but by 1640 the natives were having trouble finding enough animals in the Pine Bush to supply the growing European demand.
Split into simpler sentences: For the natives the Pine Bush was an important source of firewood and animal pelts to trade with the Dutch. By 1640 the natives were having trouble finding enough animals in the Pine Bush to supply the growing European demand.