What would be the effects of a large forest fire on soil in other places?

Question

Say a large forest fire took place. As I understand it, the smoke and ash would ride the wind and could be a health hazard even to people that are quite far away.

My question is will it damage the soil itself and its agriculture, in these places that are some distance away? If so, what will that look like (to what extent), and what distance are we talking about?

(This feels like a suspicious thing to ask, so let me just clarify that I'm asking this because this is a plot point in a book I'm writing, and I'd like to really understand what ramifications it would have outside of the specific place things are happening. I've asked related questions in other places, but I think this is the most accurate.)

Forgive me if the tags are inaccurate, I know nothing about any of this.

Answer 1

Falling ash is usually not a concern for agriculture. But the particulate matter (smoke) can harm agricultural products. Not through the soil, but by exposing the plants to smoke over long periods. In particular, many vineyard owners are very unhappy with the recent increase in wildfire smoke in the west. It taints their grapes and makes the wine less desirable or even worse, ruins the product altogether. National Geographic mentions that:

Last year, fires cost the wine industry in the United States $3.7 billion...

Wildfire smoke can travel very large distances (e.g. hemisphere), but smoke doesn't get trapped near the surface for long periods unless winds have decreased. This means that wildfires within the same geographic region will be the source of smoke, ruling out trans-continental transport as a concern. Smoke can easily pool in basins, where agriculture is prevalent, but the source of smoke is usually in the more mountainous areas around the basin. The Columbia Basin is a good example, where you can have smoke pool for long periods that came from wildfires in the Cascade mountains.

Answer 2

After Saint Helens, forest managers thought to harvest timber in the area and replant it because they assumed nothing would ever grow again. Instead they left it alone and the eruption epicenter is now the largest outdoor ecological restoration experiment. Scientists monitor it's rate and aspects of it's regeneration. Contrary to being a dead sterile environment the area is now teaming with colonizers and flowers not seen in decades; a beginning stage meadow is starting to form, Once tree seedling begin; in 20-40 years it'll be a open savannah; in 50-100 years a new woodland; in 150-20 years a new Forest may emerge. Forest fires fill a similar ecological role.....

Fire’s role in dryland ecology is well known and researched, It substitutes the role normally reserved by decomposers like bacteria and fungi. In more humid and wetter environments they break down wood/plant matter into soluble nutrients for plant uptake. In xeric ecosystems this process is slower to nearly non-existant. So fire substitutes that task by charing material into water soluble ash. Whole types of forests use this method for regeneration.... and it has various benefits. In fact every species that lives in fire prone ecosystems must have the ability to withstand at least one fire or risk losing it's place in the community.

1. The fire itself converts aged woody debris and old trees into ash, this rich mineral laden dressing will feed the next generation
2. It destroys weeds, by doing so provides available space for forbes, grasses and such to grow which is more desireable and edible by herbivorous species such as deer and game species.
3. The smoke of the fire is a chemical catalyst that may trigger dormant seeds in the soil to germinate, Now without vegetation above and the next rain, the seeds will grow competitor free. This is how Sequoia and eucalyptus regenerate.
4. The fire produces huge volumes of Ethylene gas which is a plant growth catalyst.