When you just burn a forest, you release carbon that was in the atmosphere a few years or decades ago. Those trees would die eventually, and most of the carbon would go to the atmosphere anyway.
When you dry a swamp and burn a peat bog, you release carbon that was in the atmosphere centuries ago. Under normal circumstances, that carbon would stay underground for millennia.
When you just burn a forest, you release carbon that was in the atmosphere a few years or decades ago. Those trees would die eventually, and most of the carbon would go to the atmosphere anyway.
When you dry a swamp and burn a peat bog, you release carbon that was in the atmosphere centuries ago. Under normal circumstances, that carbon would stay underground for millennia.