This entry was originally published in Spanish in ¿Cómo ves? magazine, August 2012.
At
the foot of the Cerro del Chapulín in Chapultepec Forest there is a fragrant and
beautiful park smack in the middle of Mexico City. The park is home to a very
Mexican tree species, the ahuehuete, known
for its longevity. Some of the ahuehuetes in Chapultepec have their age marked with red paint on the
trunk —400 years, 500, 600… The most ancient of these trees were there before
the founding of the Aztec city of Tenochtitlan.
I discovered the labels on the trees a few
years ago, while strolling in the shade of the old ahuehuetes. I knew that the age of some tree species is
determined by counting the growth rings in a cross section of the tree trunk.
How could the age of the Chapultepec trees be calculated without cutting them
down? I didn’t know it then, but this is the way it is done: you plug a special
drill into the trunk and turn a crank until the drill reaches the core of the
tree; out of the drill comes a thin, striped cilinder; the stripes are sections
of growth rings. You then head back to your laboratory and count stripes under
a microscope. The number of stripes gives the approximate age of the tree. To
me it was a revelation --and a relief-- to learn that it could be done without
killing the tree.
In
Search of Time Accumulated
Actually
taking the samples, however, can be complicated, as Donald Currey, a graduate
student from the University of North Carolina, discovered in 1964. Currey was
conducting research on climate change during the period paleoclimatologists call
the Little Ice Age, which runs
from about 1300 to 1850. During this period world temperatures dipped several
degrees. The Little Ice Age had consequences ranging from the biological to the
social, but that’s a different story.
Donald Currey needed samples from ancient
individuals of the species Pinus aristata, known as brisltecone pine, a
tree that dwells in the highest mountains of the southwestern United States. He
wanted to do a statistical study of the relationship between the age of the
trees and the altitude at which they grow. This would help him tell whether
climate changes during the Little Ice Age had modified the altitude of the tree
line. If he found very old bristlecones close to the present-day tree line,
then Little Ice Age changes could not have been too severe.
Since the 1950s, when Edmund Schulman
discovered that bristlecone pines keep very precise and readable registers of
climes past in their growth rings, ecologists were convinced that the oldest
individuals grew in the White Mountains of California, on the western limit of
the species’ habitat. There Schulman found bristlecones more that 4000 years
old, which he made famous in an article that appeared in the January, 1958
issue of National Geographic. Schulman
died weeks before the article was published.
Schulman’s pines became famous for their eerie
beauty. When they reach millennial ages, the gnarled branches of these trees
stretch to the sky like pleading arms, and their convoluted trunks of
dead, barkless wood seem to fly in the wind like the robes of a Biblical
patriarch. The bristlecones of California were also celebrated as the oldest
known living organisms.
Donald Currey did not go to California,
however, but to Nevada, at the center of the bristlecone habitat. There the
young scientist found what he was looking for in a grove of wondrously
old-looking pine trees growing at the edge of a deep valley carved out by an
ancient glacier in Wheeler Peak. The trees looked as aged as Schulman’s,
notwithstanding the dogma that the species only reached extreme ages in
California. The young man chose the oldest-looking tree, sank his drill into
the trunk, and began to turn the crank. Crick, crick, crick went the drilll as it bit deeper and deeper into the
wood of the Methuselah of trees. Crick, crick… CRACK! The crank snapped in Currey’s hand. The device had
broken its teeth in the rock-hard wood. Without a spare drill and with the
academic calendar against him (he had to turn in a report to the National
Science Foundation before the end of the summer), Currey went to the Forest
Service for help.
Witness
As
the first civilization was inventing the plow in Mesopotamia, in a different
continent a sapling was growing at the edge of a glacial valley. With the first
snows of the alpine winter, at close to 10,000 feet, the little tree entered a
phase of lethargic growth as it waited for better times. When the brief summer
came, it grew in a desperate spurt to profit from the sunlight and rain. The
wood it made during this accelerated growth phase was less dense than the wood
produced in the severe conditions of winter. The cycle was repeated through the
ages, and the yearly ebb and flow of growth and dormancy was recorded in the
stuff of the trunk.
Tree rings represent alternate phases of rapid
wood production, when the tree has plentiful sunlight and rain, and slow
growth, when sun and nutrients are scarce. Generally, one would expect this
cycle to match the cycle of the seasons —in which case each ring would
represent a year’s growth—, but if drought strikes in midsummer followed by
abundant rains in the fall, the tree will produce two rings. On the other hand,
if the whole year is bad —with unseasonable cold, drought and insufficient
sunlight—, there simply won’t be a measurable ring to speak of.
Tree rings, then, are not only a proxy for the
tree’s age. In their width and other characteristics, nature has written a detailed,
year-by-year history of varying weather. Growth rings are like the personal
diaries of the tree world. Matching ring sequences from many different trees to
average out errors due to double or missing rings, climatologists can build
chronologies of past climates. The tecnniques of dendrochronology
(dendros means “tree” in Greek), help scientists recognize patterns
of climate change with periods as short as one year or as long as several
centuries.
Our tree grew old as humanity went from the
Bronze Age to the Space Age. Its environment didn’t change much, except for the
weather. The land on which it grew remained stable, but for occasional
avalanches that deposited two feet of rubble on top of the original ground. The
glacier that carved the valley was already long-gone when the tree was a sapling.
But one day in August, 1964…
The
Truth and Nothing But?
What
happened when Donald Currey went to the Forest Service for help is not clear.
One version has it that the scientist asked permission to cut down the tree and
take a slab of trunk, which would be more cumbersome than the thin cilinder
from the drill, but would certainly simplify the actual counting of the rings.
According to another version, it was Donald Cox, from the Forest Service, who
suggested that Currey cut the tree, which was, after all, one of many ancient
bristlecones in the area. However it happened, Currey went back up the mountain
with pack horses and Forest Service personnel armed with chainsaws. The men
brought down the ancient tree.
Very satisfied —or perhaps not—, the young
researcher took a large wooden slab more than two meters in diameter down the
mountain to his hotel in Baker, Nevada. The next day he set the slab on a table
outdoors, took out a magnifying glass and some sandpaper to bring out the grain
in the wood, and started counting. By the end of the first day he had counted
back to the Middle Ages. This did not surprise him, because he already had
core samples from 113 trees from Wheeler Peak. He knew they were really
old. Currey counted on. The following day he had reached back to the time of
the Roman Empire —and he was not even halfway through the counting.
In 1965 Donald Currey published a paper in the
journal Ecology. By that time his goal had
changed from building a chronology of the Little Ice Age to proving that
Schulman had been wrong to believe that the oldest individuals of the species Pinus
aristata were to be found only in
California. Here is what Currey writes regarding the tree he named WPN-114
(the 114th tree from Wheeler Peak, Nevada): “The tree-ring series contains both
distinctively thin (microscopic) rings and difficult-to-count incomplete (locally
absent) rings.” This did not daunt the scientist. He went on counting rings for
one week. The article continues: “The derived radius measures 2,280 mm to the
pith, 100 inches above the original base, and encompasses 4,844 counted rings.”
Then, in the same serene, unfathomable monotone, he adds: “Allowing for the
likelihood of missing rings and for the 100-inch height of the innermost
counted ring, it may be tentatively concluded that WPN-114 began growing about
4,900 years ago.”
The impersonal drone typical of scientific
papers conceals what the author must have felt when he discovered that his tree
began life before the birth of Greek civilization, and even before the Ancient
Empire in Egypt. Schulman’s oldest
specimen was 4,600 years old. Currey had found one that was even older… and he
had cut it down.
“Murderer”
It
was Currey’s misfortune that the people of Baker had grown fond of the trees in
the old grove on Wheeler Peak. Darwin Lambert, an official with the Forest
Service, had formed an association to promote the creation of a national park
in the area to protect them. To make things more poignant, Lambert had even
named every individual tree. Currey’s was called Prometheus.
In 1966 Darwin Lambert, who by then had
nourished the park project for years, heard that a researcher from North
Carolina had found in Wheeler Peak the oldest living tree in record. Lambert
felt a jolt of excitement at the possibility that it was one of his trees. He
procured a copy of the journal where the researcher had published his paper and
his heart sank when he understood that the tree in question had been destroyed.
Understandably, Lambert flew into a rage and wrote an article in a local
newspaper. The media and the public went after Currey, accusing him of killing
“the oldest living organism in the world.” Overwhelmed, the young man hid in
his university and tried to keep a low profile, as scientists will after a
clash with the media.
Now, Currey killed (the term may be too strong
in its overtones) the oldest living organism known at the time, which does not necessarily mean that Prometheus was
the oldest tree in the world. We do not know the age of every tree in
existence. There may be others that are even more ancient. It is misleading to
call Prometheus the oldest living organism in the world. And exactly what is
an individual organism? Many plants
reproduce by a kind of natural cloning mechanism consisting in throwing
offshoots that are genetically identical to the original plant. The offshoots
form a clonal colony. One can argue that the clonal colony is an organism that
lives on even if the individual plants die. There is a clonal colony of
creosote bushes which we know for certain to be 11,700 years old. In the state
of Utah there is a colony of quaking aspen trees linked by an enormous root
system that has lived for some 80,000 years (though not one of the individual
trees is more than a couple of centuries old). Prometheus was the oldest living
non-clonal organism known in 1965, not simply the longest-lived being on the
planet.
One more detail: Currey found on Wheeler Peak
the remains of pines of the same species scattered all over the place. The
trees had been cut down without consideration by surveying expeditions in the
19th century. Some of those trees were probably older than Prometheus. Currey
was “appalled by the destruction.” This was not contrition enough. In the eyes
of the public he remained a heartless murderer.
Two
Martyrs
Today
bristlecone pines are recognized as useful to science. In 1970 a researcher by
the name of D. K. Bailey found variations in the form of the pine cones and
needles of bristlecones from different regions. Bailey proposed dividing the
species in two: Pinus aristata and
Pinus longaeva. Climate
chronologies based on the growth rings of this species as well as on pieces of
deadwood (dated by radiocarbon) reach almost 9,000 years into the past. The
oldest living non-clonal organism known today is one of Schulman’s
bristlecones. Named Methuselah, it is 4,844 years old as of 2012 and its
location is kept secret.
There is another turn of the screw in the story
of Donald Currey and the Prometheus tree. Darwin Lambert, the national park
advocate, and his group never could get the US National Park System to approve
the recommendation to create a park in the mountains of Nevada. The area’s
resources (mining, hunting, pastures) were too rich to give up in the name of
tourism and the environment. Powerful lobbies opposed the park. The death of
Prometheus gave the project a new edge by focusing attention on the need to
protect bristlecone pines. Currey’s error contributed at least a little to tilt
the balance and finally, in 1986, the Great Basin National Park was created.
Donald Currey endured as best he could the
grief that his mistake caused him. At the time of his death, in 2004, he still
was not over it. As for Prometheus, all that remains of the once proud ancient
is an inglorious stump.
