Again, the issue is that once you burn fossil fuel, you are not turning it into fossil fuel in any meaningful amount of time.

On the other hand, let’s say that a field used for producing plants for biofuel does not capture any carbon at all to simplify. So deforesting an area releases all the carbon a forest held. The difference is that the fossil fuel gives you energy one time, while the field produces it yearly. We need energy yearly. So if you deforest an area for biofuel, you release CO2 from deforestation but all the CO2 released in the future is what was recaptured by the plants. It is one time CO2 release for perpetual energy delivery. If you go with fossil fuels, you will keep burning more and more every year until it is much worse than deforesting an area.

So reforesting can capture CO2 already released, but that only offsets fossil fuels for some period of time. Even if you cover the whole planet in forests, there is a finite amount of fossil fuels you can burn before it is negated. That is why eliminating fossil fuel use, and quickly, is far more important than protecting forests. Once you burn fossil fuel, you can’t recapture it into fossil fuel and would have to increase fores area permanently to compensate.

the alternative to burning biomass would need to have very high emissions in order to come out ahead.

Not really, that’s the point. Soil has a max capacity of carbon it will hold. Just like biomass. So even if the fossil fuels release tiny amount of CO2, they release it continually vs deforestation releasing it one time. The only thing that changes is how long it takes for biomass to break even. But after thousands of years, the one time big release will always turn out better than continual small releases.

Of course, avoiding both deforestation and fossil fuels is even better.

It is superior if letting the forest grow means using fossil fuels. That was the point of my comment. It releases CO2, but only once and then is sustainable without additional CO2.

Of course, having the forest and e.g. nuclear power would be even better but that does not work very well for mobile applications, such as vehicles.

A very good question.

It is a very common misconception that trees and plants just always absorb CO2. The Carbon © in CO2 does not just disappear when plants produce Oxygen (O2). Plants use it as material to grow themselves and their fruits. Once they are fully grown, they don’t really absorb any more. So if you burn a tree in a fireplace and grow a new tree in its place, the new tree will eventually re-capture all the CO2 burning the wood released as it grows. This works even better with fast growing plants used for biofuel. The CO2 released by burning biofuel is re-captured when you grow more plants to make more biofuel.

So chopping down a forest to create fields is bad in the short term since it releases and does not recapture the CO2 from the trees, but is sustainable in the long term since you “recycle” the same Carbon.