Thick bark.
Trees in fire-prone areas develop thicker bark, in part, because thick bark does not catch fire or burn easily. It also protects the inside of the trunk, the living tissues that transport water and nutrients, from heat damage during high-frequency, low-intensity fires.
Ponderosa pine (
Pinus ponderosa, also commonly known as the bull pine, blackjack pine or western yellow pine)
is a great example. This signature tree in the western United States has a thick and flaky bark, sometimes compared to pieces of a jigsaw puzzle, which perfectly withstands a low-intensity, surface fire. The species also drops lower branches as the trees grow older, which helps prevent fire from climbing up and burning the green needles higher up the tree.
Fire-induced sprouts.
This fire-survival strategy allows for the complete destruction of above-ground growth. Typically, species that regenerate by re-sprouting after they’ve burned have an extensive root system. Dormant buds are protected underground, and nutrients stored in the root system allow quick sprouting after the fire. Shortleaf pine (
Pinus echinata, also occasionally called southern yellow pine or the shortstraw pine) employ this technique.
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more:
https://www.nationalforests.org/our-forests/light-and-seed-magazine/how-trees-survive-and-thrive-after-a-fire
Add NickB79's remark in post #4, and it sounds like Ponderosas interspersed with other species which do
not shed lower limbs would be more prone to crown ignition than Ponderosas in more homogenous groves, and thus less likely to survive a fire. So the isolated grove referred to in the OP sounds like it might be a common phenomenon.
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