@Vishsai good thinking! Some red flags though -

1. 1000 saplings may produce enough oxygen for 1 tree. But what if none survive?

2. Who takes care of those 1000 saplings?

3. What if grasslands are destroyed to plant saplings (which happens now)

4. What if non native saplings are planted (which happens now)? If they actually grow on to be trees, it's abigger disaster for the biodiversity

So I say that thinking about it only in terms of oxygen will allow the authorities to misuse it further.

@Vishsai sadly not a straightforward question. Planting has to be done carefully using native plants, on suitable habitat and with a lot of post planting care. Most saplings don't survive. It is best to prevent felling of old growth trees than think of replacing it with saplings.

However, guidelines do exist on restoration of degraded habitats, but that is not a substitute for clearing forests