No, not that burned land. The stuff that burned back in 2004 and 2005. Apparently, more land burned back in the mid-2000s than in 2019 (*). Has that land been in continuous use by cattle ranchers or soybean growers since then? Or did it get used for a few years and then abandoned? If the latter, does the forest start to recover? Or is the soil too stripped to regrow in any kind of human-scale timespan?
(*) Strictly speaking, what that graph says is that there were more fires in the mid-2000s, but it seems a reasonable extrapolation that more land burned then.
If the land is intentionally burned, that generally means that it is going to be put into (or back into) cultivation or pasture. If it is not, then it reverts to second growth. Forest of sorts will regenerate, but it won’t have nearly the same value for biodiversity for (probably) centuries.
One problem is that tropical soils are often low in necessary minerals and nutrients. If they are allowed to revert to second growth they can recover. But if they are maintained as cultivation or pasture for too long, it can take much longer for them to recover.
I think it’s generally acknowledged that the vast majority of the Amazon fires are intentionally set. And I understand that it’s put into production or pasture - I said as much in the OP. The question is if it’s still in production/pasture 15 years later, or if it’s been exhausted, abandoned, and regrown.
It varies but the use for farming can be just a couple seasons, plus or minus. For pasture it’s longer. More like the usability fades and fades and fades. Fewer cattle are kept on the land until the effort to do things like roundup the cattle from time to time isn’t worth it and then the last are moved on.
My understanding of why rainforest soil is so bad is because the ecosystem is so energetic that any nutrients in the soil or fallen trees/plants are quickly sucked back up into new growth. The constant rains have also leeched out most minerals, so the plant life has evolved to absorb and retain as much energy as possible as quickly as possible. Burning the forest is a way to return some of those nutrients stored in all the plants into the soil. I believe charcoal helps soil retain water better too, but without a strong plant canopy it’s much more likely to wash away in the heavy rains. Still, since nearly all of the biomass of a rainforest is in its canopy, the “fertilizer” obtained from burning it doesn’t improve the soil all that much.
