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A closed-off dell ringed entirely by mountains is smothered in smoke at 900°F from a dragon. After suffocating the forest, a magical barrier seals them in. It is invisible but doesn't allow airflow with the outside world. It bulges up or inward to maintain pressure equilibrium, but nothing escapes. The barrier is a perfect conductor of heat and light.

  • Several creeks trickle in from the mountains and leech into the soil, the barrier doesn't stop this.

  • This is a temperate climate with a dense mix of deciduous and evergreen trees; the season is late spring with optimum daylight. A light morning fog covered the forest at the time of the attack, when everyone was asleep.

  • The smoke is normal wood fire smoke with carbon monoxide, carbon dioxide, and soot. It comes in rapidly but not instantly, the dome traps most of the smoke in before it can be drawn out by convection (50% air is displaced, again).

Survivors if any will need to find air pockets and restrict their breathing, but that isn't in this question. I plan on having a few survive. But the question is about survival of the forest which spans 300 acres and is at least 50% depleted of air when sealed. Estimated air is 20 million m$^3$

If this dome stays and the forest survives, how long would it take for the dome to become irrelevant (the oxygen has returned)?

I know the CO$_2$ will increase vegetation yield linearly with percentage increase, but it has to first absorb the heat energy of the smoke within the existing mass, which may wilt green leaves and delay replenishment.

Balancing the several factors makes this trap a problem, where I want the animals to be endangered but keep the forest alive. The dragon is protecting it by smothering the animals. The listed magic is the limit that can fit into the plot: Smoke-breathing dragon, and a magic barrier. No other magic can apply. Will the forest ultimately survive (or even thrive)?

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  • $\begingroup$ Can you clarify? The title says "flash-heats," the body says "smothered in smoke at 900°F." Are the trees burning when the barrier goes up? (I expect that they would be.) If so, and there's any restriction in the flow of oxygen from the outside at all, everybody and everything inside is dead in minutes-to-hours depending on the height of the barrier. The fire will deplete the oxygen (and put itself and all other breathing things) out. If you want this to simply be ignored, please add a bullet to state this as a condition of the Q. However, those living things (bugs...) are part of recovery. $\endgroup$
    – JBH
    Commented Feb 22, 2022 at 4:11
  • $\begingroup$ I do not believe that the trees would be burning without an actual ignition, that's not the plan; this is smoke only. The conditions are not specified as drought, I don't think it should be a problem. 160-year-old dried oak has an auto-ignition temperature of 779° F when exposed for between 344 and 365 seconds. The oxygen id being depleted as well so fire should be quickly smothered. Live trees will have 80% moisture, needs a long exposure to ignite. $\endgroup$
    – Vogon Poet
    Commented Feb 22, 2022 at 4:38
  • $\begingroup$ The ignition temperature for a ponderosa pine needle is as low as 327℃ (620℉). Keep in mind, I'm not arguing the point. If it doesn't matter, say so in the question. If it does matter, specify the conditions of the forest (type of trees, time of year, humidity and moisture, etc.) - but I think you'd get further to simply state the condition so it isn't considered as part of the answers. $\endgroup$
    – JBH
    Commented Feb 22, 2022 at 4:52
  • $\begingroup$ I'm certain something will hit ignition temperature, but to kill the forest it has to burn. To auto-ignite it has to be exposed for an amount of time, normally in hundreds of seconds; and to burn it needs oxygen. Maybe it will and maybe it won't; maybe pines will lose their needles and oak will survive. I don't know these things. Heat is in the gas, wood is dense and can absorb lots of heat. My thought is that the heat will drop quickly unless there is active combustion. Will that happen? That's the intent of the trap. $\endgroup$
    – Vogon Poet
    Commented Feb 22, 2022 at 4:58
  • $\begingroup$ type of trees, time of year, humidity and moisture, etc are fairly defined in the question. $\endgroup$
    – Vogon Poet
    Commented Feb 22, 2022 at 5:04

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Many of the trees in a mixed deciduous forest will die at the leaf and limb level but their trunks and root systems will survive; the flash burn will effectively be a coppicing cut over for those plants, they'll recover, sluggishly in the year of the burn because of their sap already being high but quite vigorously the following spring.

The evergreens are a different story, when their green tips are killed they simply stop growing. A ~480°C flash over is going to kill the growth tips of most/all their branches, it'll leave a lot of evergreens standing, even with green needles but it is a forest of zombies. The trees will grow no farther and because they only leaf on new growth once they drop the last of their existing needles they will slowly die altogether. This kind of kill is a bad one for the natural regeneration of the woodland, the evergreens are still shading their neighbours and their potential offspring and will for several years to come. The seeds of many of the evergreens will start to sprout the next spring, (in fact in managed woodlands where fires have been suppressed seedling overload is a major cause of wildfire spread), but they'll be competing for light with trees that are effectively dead so their growth will be slowed.

I think the dome is going to have an effect on atmospheric composition for about a year, possibly nearly two, but it will be highly dependent on the chlorophyllic density of the recovered canopy in the first year.

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