That's not how it works with plants. If you or a cow can eat them, that means that they are already done capturing the carbon because that's what they are made out of.

They are done and we still got too much atmospheric CO2, now you burn them. Feel free to insist they captured it in the past hundred years but it’s really a distinction without a difference in this situation. You don’t get a free pass on the CO2 you are releasing now.

If you do not burn them, the plants will die and get composted into soil. Soil itself will decompose and release that carbon back into the atmosphere. In temperate climate, this happens in a decade or less.

The cycle keeps running with or without humans doing the emissions part.

So lets focus on the extra carbon that we dug out and inserted into the cycle.