Do trees ever die of old age?
My boyfriend says plants and trees have natural lifespans like animals. I say if a plant doesn't die of disease, drought, famine, fire, etc., it will not die. Look at those age-old trees out in California. Please help us settle this argument.
Death, disease, drought, famine — at last a question that speaks to me. To simplify matters, let's just talk about trees. One may speak of trees having life spans, in the sense of having an average life expectancy. The Encyclopaedia Britannica notes that the "lifespans of trees, like those of all organisms, are limited." But while this is certainly true — no tree is immortal — it's also deceptive. Trees may have life spans, but they don't have fixed life spans, as animals do. It is reasonably certain that no human, no matter how coddled, would survive past some definite point — say, 120 years. But this cannot confidently be said of trees.
The most striking illustration of this is the bristlecone pine, Pinus aristata. A 1948 field guide noted that bristlecones reached maturity in 200-250 years, with "extreme ages of 300-375 years." Yet only 10 years later a researcher discovered a stand of bristlecones whose average age exceeded 4,000 years and in one case 4,600 years.
Other examples are less dramatic but still instructive. Red maples live 80-250 years, American chestnuts 100-300, white oaks 300-600, bald cypress 600-1,200. These extremely broad ranges suggest that assigning a "life span" to trees is merely a statistical convenience rather than a reflection of an inherent limit. It would not be surprising (to me, anyway) if much older examples of these species were found.
Trees endure as long as they do basically because they're nonhierarchical organisms. In animals, all vital functions are controlled by the central nervous system, the guiding element of which is the brain. When the brain dies, so does the animal. By contrast, vital functions in trees are decentralized. A large part of the tree can die, and indeed routinely does die, without killing off the tree as a whole. Most of a mature tree is dead except for a few layers under the bark.
Trees have an astonishing capacity for survival. The oldest bristlecone pine is described as "a gnarled jagged piece of deadwood … overlaid on one side by a narrow strip of living bark barely sufficient to connect the few remaining living roots with its few remaining living branches. Yet every year the sap rises" (Feininger, 1968).
All trees die eventually, of course. Four thousand years is old compared to the life spans of gossamer creatures like ourselves, but in the context of geologic time it's the blink of an eye. As they get older trees become more susceptible to disease, pests, and other perils, and inevitably these take their toll. But think how different our conception of mortality would be if we were like trees: You probably won't last past 375 years, Jack, but play your cards right and you might squeak out 4,600. I don't know about you, but I'd definitely watch my weight.