You are aware that "temporarily" in this context is the lifespan of a tree, right? Trees live anywhere from several decades to 20+ centuries, and their remains, once broken down, provide nutrients to the soil so more trees can grow.
Also the tree is not capturing carbon, instead emitting, half of the year if not planted in the optimal places near the equator.
And it's carbon neural or negative once almost fully grown.
Basic biology should tell you that the only thing that counts for carbon capture is biomass added. Anything that the tree does that doesn't permanently add to its mass can't capture carbon permanently. Hence, once a tree stops growing, it stops capturing carbon. It still respirates because it does things that require energy, but any carbon it captures doing so is released fairly quickly again, e.g. when the leaves it produced in spring fall off and rot. Of course many trees keep growing a little even after they reach maturity, but the rate of growth is minuscule. A mature stable forest stores a large amount of carbon, but it hardly captures any more.
Anyway, the land we have is limited. You literally can't cover the planet in one big forest to capture the gigatons of carbon we have released. You have to do active forest management and store the carbon somewhere stable, for example as biochar.
