That obviously depends with what happens with the trees that could not have been preserved. If you burn a tree you set almost it's entire absorbed CO2 free. On the other hand, a recently planted tree has absorbed almost nothing - it will take decades if not longer to grow to a big one - reaching the level of absorbed CO2 of the other tree before it has been burned.

Nevertheless, a tree at the place of an older one can help binding CO2 when the old tree is used such that the CO2 is not released to the atmopshere, such as for a well-crafted table (which could be used for decades, too). But don't forget that it usually is not just removing one tree - usually big areas are cut out, which includes the huge ecosystems around trees in untouched nature.

Though, always keep in mind, this is not a choice. The goal should be to preserve as much as possible (especially untouched ecosystems) as well as planting as much as possible.

There's more to climate change than CO2... Forests create micro climates; prevent soil erosion; help fixate water and nutrients; produce food for local populations, thus providing them income and reducing need to ship as much food to rural areas; improve yields of agriculture, so you don't need to water as much, or use as much ferilizer... And Ecosia is invested is projects to help with all of this (read their blog).

This single track kindset of climate change fight is why we get so much green washing.

CO2 isn't the only reason to take care of forests. If we replace a naturally grown forests with newly planted one we destroy an existing thriving habitat and replace it, in most cases, with a monoculture. This has tragic impact on biodiversity.

Here's a good article you might want to read. It also says that natural forests are actually better at capturing CO2.

https://www.nature.com/articles/d41586-019-01026-8

That's probably true, but when a forest is burned, that's decades of absorbed CO2 that goes back to the atmosphere, which would take another decades to be absorbed by the new trees.

When a forest burns, most of what burns is new growth: grass, leaves, needles, branches, etc. Rarely do trees fully incinerate, even in the hottest spots. I imagine the charred matchsticks left behind still contain the majority of a tree’s carbon.

The dead tree will eventually decay, releasing all its carbon. When talking about deforestation, this means reusing the land for something else.

Old forests better retain water and thus are able to grow better - marginally accumulate more biomass. I'm NOT against planting trees but against overdoing it as I explain in the other comment.

https://envirobites.org/2019/09/24/old-is-better-than-young-...