Answer: Heat stress takes only a few days to show up so what you're seeing might be just that. Trees from coastal climates or areas with high humidity and summer rainfall are most prone to damage during dry hot weather. The popular Coast redwood (Sequoia sempervirens) never tolerates drought. It is normal for older needles to turn brown and drop in the summer. If the trees are underwatered this normal browning will be greatly exacerbated and the needle drop will be considerable, stressing the tree. As the weather returns to normal, your tree should recouperate. Look for new growth next spring in the areas it lost foliage this summer.
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