[1) Because the trees are important for more than just some of our oxygen production. Do you have any idea how many of the world's ecosystems are reliant on trees? If there were no trees anymore there would be a mass extinction event
That's cute, we will be fine. There are more trees on earth now than ever.
Although, you probably still think Mongolia and the Great Plains need replanting.
1) I am sick and tired of people that do stupid things and say "I'm sorry" or "help me! because I am an idiot". You don't care about these NOW because you don't have to. If only YOU die, big deal - no big loss. If EVERYONE on the planet dies, that IS a big deal.
2) The "green life" on land is arguably much easier to kill than in the oceans. The oceans are like 75% of the Earth. Whatever affects them would have to be BIG and last for a VERY LONG time. On land, everything like a forest fire (see the one in Canada ATM) or a drought (see "the Great Dust Bowl) can deforest a location VERY quickly. It will then take YEARS to replace the plant life.
3) Farming also would cause problems because (a) periodically, these BIG plants (like corn) would be cut down reducing the oxygen they produce until they regrow and (b) there would be competition of oxygen vs food.
4) IF we were to be relying solely on land plants for oxygen, we could be wiped off the Earth at just about any time.
5) Finally, as algae is THE bottom of the food chain in the oceans/lakes, if it disappeared, most likely ALL sea life (shrimp, fish, whales, etc.) would die. So, we would TOTALLY rely on land plants and animals for food increasing the need for plants. Animals and people rely on plants for food and oxygen.
6) Anyways, IMO, who cares what you think. Obviously, you are in the group of people that don't care about humanity (its survival). I had another link about "killer asteroids" that FEers don't believe in because, hey, the sky is only a couple thousand miles up. Someone one else had the same total disregard for protection from them as you do about trees. Oh, well.