Trees live longer than any other organism on earth. This is because they are able to respond to attacks by pathogens and pests and continue to grow, some for thousands of years. However, trees also are subject to attack by pathogens. Two major U.S. tree disease epidemics of the 20th century, chestnut blight and Dutch elm disease, have killed millions of trees in forests and towns. The stresses of air pollution, salt spray, soil compaction, and monoculture also can shorten the lives of urban trees.
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