What is a company's obligation to contribute to the sustainability of natural resources?

Under law? Depending where and what biz is there is NO obligation, or little if any in most cases.

Under morals, aka higher principles most bussinesses would just have to close.

Under Biblical principles, to subdue is one thing, to destroy is another. Much can be done but won't be because of cost/politics over logic. Sometimes that too is a natural resource, it's called freedom and or liberty and someone is using a lever for an alternate motive just saying it's for the 'trees’. Other cases it's plain and clear destruction for profit and nothing is said.

Record forest fires have occurred in west, some of it because environmentalists interfered with forest management to the point of cost in court and in the field leaving nothing to do. Areas that needed undergrowth and deadwood removed were kept untouched decades. Red tape and global warming made fuel stack up.

they deliver oxygen to the blood

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.