That'd be basically a tree plantation, but a real forest is an extremely complex ecosystem, whose soil builds up and evolves over hundreds of even thousands of

That'd be basically a tree plantation, but a real forest is an extremely complex ecosystem, whose soil builds up and evolves over hundreds of even thousands of years where microorganisms, mycelia and trees' root systems interact, cooperate, share nutrients and water. The same goes for the canopies, where a whole other ecosystem lives in it's own, with some species (animals and plants alike) never touching the ground of the forest for their whole existence. Forest are an incredible carbon sink and removing old growth will dry up the soil and cause outgassing of the captured carbon within a quite short period of time, cause weather induced soil erosion and destroy the former water retention capabilities, leading to more floodings.