What very old trees can teach us about life, death, and time.
Jared Farmer writes:
What’s the oldest known living thing, and how do we know? Why should we even want to know? The explanation is a history of curiosity and care. It’s about our long-term relationships—spiritual and scientific—with long-lived plants, as long as long can be. It’s all about trees.
A tree is a plant that people call a tree—a term of dignity, not botany.
Although people construct the meaning of “trees” and assign age value to the vascular plants they call “ancient trees,” people cannot themselves create life that grows in place for centuries. Exclusively, solar-powered organisms enact that miracle. Among plants, there are ephemerals, annuals, biennials, perennials—and, beyond them all, perdurables, thousand-year woody life-forms.
As a rule, gymnosperms (flowerless plants with naked seeds) grow slower and live longer than angiosperms (flowering plants with fruits). Gymnosperms include ginkgo (a genus of one), cycads, and every kind of conifer—including yews, pines, firs, spruces, cedars, redwoods, cypresses, podocarps, and araucarias. All these lineages began hundreds of millions of years before the divergence of angiosperms. In effect, the newer, faster competition forced slow growers to retreat to exposed sites and poor soils, adverse niches conducive to oldness. Five thousand years is the approximate limit for nonclonal living under adversity. In plants, the potential for extreme longevity seems to be an evolutionary holdover from the deep past. Only about 25 plant species can, without human assistance, produce organisms that live beyond one millennium, and they are mainly conifers of primeval lineage. The cypress family contains the most perdurables, followed by the pine family. Many relict conifers hang on in limited, vulnerable habitats. The ice ages didn’t help their cause. In general, neither did humans, with their technologies of fire, domestication, and metalworking. Of some 600 conifer species, roughly one-third are endangered, with many genera reduced to a single species.
A gymnosperm doesn’t so much live long as die longer—or, live longer through dying. The interior dead wood—the heartwood—performs vital functions, mechanically and structurally. In comparison, the thin living outer layer is open to the elements. If damaged by an extrinsic event such as fire or lightning, this periderm doesn’t heal or scar like animal skin. Instead, new cambium covers the injury, absorbing it as one more historical record alongside its growth rings. Thus, an ancient conifer is neither timeless nor deathless, but timeful and deathful. A few special conifers such as bristlecone pine can live through sequential, sectorial deaths—compartmentalizing their external afflictions, shutting down, section by section, producing fertile cones for an extra millennium with the sustenance of a solitary strip of bark. The final cambium has vitality like the first. Longevity doesn’t suppress fecundity. Unlike animals, plants don’t accumulate proteins that lead to degenerative diseases.
The strongest correlation with long life (elongated death) is chemical. Longevous conifers produce copious resins—volatile, aromatic hydrocarbons like terpenes—that inhibit fungal rot and insect predation. Chemically, bristlecone is off the charts. Its high-elevation habitat offers additional protection from enemies, competitors, and fire, given that they tolerate dryness and cold. In habitats with chronic stress, conifers grow slower and stockier. Slow woody growth generates more lignin, another organic polymer with defensive properties. Stress-tolerant plants prioritize stability over size. Their stuntedness is equal parts adaptation and tribulation.
Regrowth is another pathway to oldness, an adaptation that appears in both gymnosperms and angiosperms. Certain single-boughed woody species—notably ginkgo, redwood, yew, olive—can recover from catastrophic damage, even the death of the bole. These trees never lose their ability to resprout and regenerate. At the organismal level, they do not senesce, meaning they don’t lose vitality with age. In theory, such a plant is internally capable of immortality, though some external force inevitably ends its life. With particular species and cultivars, humans can force rejuvenation through grafting, pollarding, or coppicing. Plants that normally die young may live long under horticultural care.
The price of longevity is immobility. At the organismal level, a plant cannot migrate like an animal. Its localism is total. Trees take what comes until something indomitable comes along. Extrinsic mortality may result from a distinct catastrophe, such as fire or gale, or multiple, cumulative stressors. There are limits beyond which even the most deeply rooted organisms can no longer function. Thresholds of water, salinity, and temperature are absolute thresholds.
Does a naturally occurring tree of great age have value in itself? Foresters and forest ecologists have long debated this question. A century ago, technicians used words like “overage,” “overmature,” and “decadent” to describe standing timber past its prime. Commercial managers saw tree life as individual and rotational, and considered postmerchantable growth to be a biological waste of time. Their business—international markets for wood products—encouraged uniformity in age and size. By contrast, forest ecologists studied the communities in, on, and under each tree—each a world in itself—and saw forest life as processual. The cycle of life required dead and dying trees. Today, foresters meet ecologists halfway: Old trees provide nutrient cycling, carbon storage, and other “ecosystem services.”
Perdurables are so much more than service providers. They are gift givers. They invite us to be fully human—truly sapient—by engaging our deepest faculties: to venerate, to analyze, to meditate. They expand our moral and temporal imaginations.
In mythical form, trees appear in creation stories, present at time’s beginning. In graphical form, they represent seasons, cycles, genealogies, algorithms, and systems of knowledge. An olden bough is a bridge between temporalities we feel and those we can only think. This is why Darwin imagined millions of years of evolutionary history as a wide-spreading Tree of Life. Most profoundly, select living conifers—ancient organisms of ancient ancestry—are incarnations of geohistory. Volcanic eruptions, magnetic field reversals, and solar proton events leave signatures in their wood. Through tree-ring science, we see how woody plants register cyclical time and linear time, Chronos (durations) and Kairos (moments), climate and weather, the cosmogenic and the planetary. As multitemporal beings—short, long, and deep time together, in living form—perdurables allow us to think about the Anthropocene without anthropocentrism. They grant emotional access to timefulness.
Full article available at Nautilus.
The “adaptations” that contribute to trees’ longevity have the hallmarks of design, to enable the organism to weather various threats to its existence. The persistence of these living things is remarkable. The author’s description of some trees reminds me of Tolkien’s description of elves: immortal, but still subject to death by violence. Stewarding Earth’s resources by appreciating the value of these longest-lived keepers of history is commended to us by wisdom.