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| Dead box elder (Acer negundo) |
showed an interesting behavior after a prescribed burn. It leafed out normally
in the spring and produced a healthy crop of samaras (seed carriers). Then in
early June all the leaves suddenly died! (see photo)
relatively heat resistant. It appears that the cambium, which supplies water to
the leaves, may be more fire sensitive and was heat girdled by the burn. So the buds
opened and formed normal leaves, but as they expanded their demand for water could not be met. With the advent of summer heat, the leaves (and the tree) died.
by heat girdling. About ten years ago we had a few smallish red maples on the north side of Toby’s Prairie. They appeared to survive a spring burn
fine but in midsummer the leaves turned red and dropped and the trees died.
girdling: smallish white oaks in our savanna appeared to survive a hot fire
reasonably well. The leaves came out in early May normally but a few weeks
later the lower leaves turned brown and died. The upper leaves remained fine.
Interpretation: the fire was hot enough to heat girdle the lower leaves but the
upper leaves were far enough away from the heat to be unaffected.
years, in two separate savannas.
to U.S. Forest Service literature, the lethal temperature is about 60 C (140
F). But it looks like dormant buds may be able to withstand higher temperatures than
the small twigs that supply them with water and minerals.