The annual emissions from forest fires vary greatly between years. In extreme years the direct emissions from forest fires can be as high as 250 million tonnes of CO2 equivalents. These are just the direct emissions. Forest fires also kill trees, so these trees will decompose in subsequent years and release more carbon dioxide to the atmosphere, but they will also rejuvenate the forest dynamics, allowing new forests to grow back.
If we had a system of constant forest fires, then the area burnt would be offset by the area regrowing and the emissions would be balanced by regrowth, but unfortunately, what we have experienced over recent years is a dramatic increase in the area annually burned, as was said earlier, so that has resulted in increased emissions to the atmosphere.