I would have to see the sentences in order to help you out
Answer:
The main problem with relying on nature to start a flame was that Fire was likely hard to find, requiring a "long journey and a deal of trouble."
Explanation:
If nature started a fire, the people would have to carry that fire to the place where they lived at that time and guard it as much as they could. These journeys were sometimes long and dangerous and it was not a reliable way of procuring fire.
The tree is biotic because it is was or currently is living.