what will happen if trees grow too much in the earth?

The last time trees reigned supreme was the Carboniferous Period, when oxygen levels in the atmosphere were the highest they've ever been in Earth's history. Oxygen is very flammable if it is present in large enough quantities, so an oxygen-rich environment would easily burn if ignited by, sayyy... lightning. Arthropods such as insects have spiracles through which they gather oxygen. These spiracles can only allow so much oxygen absorption at once, so having a more oxygen-rich environment would allow arthropods to grow much larger without being starved of air. Then, there's the decay- plant matter would build up and create layer upon layer of coal.

So, basically: Forest fires. Big bugs. Black rocks. Sounds like a nightmare.

It would cause the earth to cool (opposite of global warming) - I don't think it will be a problem with man on the planet though

No effect on g

That would be a good thing because. there would be more o2 for humans.

rip buildings and roads apart