The life expectancy of our compatriots, threatened or not by the Covid-19 pandemic, is today at the heart of the discussions. It refers more generally to the question of longevity, inscribed in the genetic heritage of animal and plant species, whose secrets scientists are trying to unlock.
In animals, attention has been directed in particular to the proteas, these strange and fascinating cave amphibians, weighing about twenty grams and capable of living up to a hundred years, as long as an elephant.
VIDEO: The mini dragon of the alpine lakes (National Geographic Wild France / Youtube 2016)
But it is also towards the trees that we must turn. Among these, the famous awned pines of California hold the age records, with living individuals of 4500 or even 5000 years old, therefore contemporary with the pyramids of Egypt.
These pins (the Great Basin Bristelcone Pines for Americans) of the species
Pinus longaeva, flourish between 3000 and 3800 meters above sea level on the arid windswept peaks of the
White Mountains Californians, marked by intense winter cold and summer drought.
Part of the monospecific stand showing very scattered trees. However, we note the emergence of young pines © Thierry Gauquelin, CC BY-NC-ND (via The Conversation)
Methuselah and Prometheus
In 1957, biologist Edmund Schulman counted some 4,600 dark circles – the annual growth rings – on one of the pines of these mountains, creating the sensation by identifying the oldest living tree on our planet, the aptly named Methuselah.
This also highlights the interest of dendrochronology, based on the study of these rings, true pages of history allowing a reconstruction of the climate for nearly 8000 years.
But it’s another awned pine, nicknamed Prometheus, this time native to the mountains of Nevada, further east, which has been credited with over 5,000 years of age. An extreme longevity which came to an abrupt end: in 1964, as part of a study on the Little Ice Age, a young student, Donald Currey, spotted this tree already known to specialists and
kills it to be able to easily count the rings on the trunk section. The age record falls at the same time as the tree disappears… leaving Methuselah to become the oldest living tree.
Secular guardians of a timeless space
No need to see this venerable Methuselah, no more impressive than the others, to appreciate this grandiose landscape of the White Mountains.
Tortuous trees, with twisted and complex trunks, where the bark stripped by centuries of blizzards has given way to the veins of a wood hesitating between black, yellow and white.
Shy trees, followers of social distancing, regularly spaced between beaches of dolomitic pebbles, some vigorous and green, others having with great difficulty preserved only a few branches covered with short needles and others still, dead, ghosts or candelabra, rot-proof age-old guardians of a timeless space.
Distinctive twisted trunks of awned pines © Thierry Gauquelin, CC BY-NC-ND (via The Conversation)
Living to a very old age in a hostile environment
The strategy of extreme longevity is based on three rules, sublimated by the awned pine: avoid competition, economize, accommodate.
Avoiding competition means first and foremost avoiding that of other tree species. These pines are thus the only ones be able to grow on these soils nutrient-poor skeletal dolomite. But it is also necessary to limit competition from congeners. The pines are sufficiently spaced from each other so as not to shadow each other literally or figuratively. The root network of each of the individuals explores a circle of soil around the tree which will not encroach on that of the neighbour.
Another advantage at this almost regulatory distance is that a fire caused by lightning reaching one of the trees will not spread to the entire stand, especially since the low vegetation between the trees is quite sparse.
Twig with very resinous dark purple cones © Thierry Gauquelin, CC BY-NC-ND (via The Conversation)
There remains, however, competition from insects, fungi, bacteria, attacking the vegetative and reproductive system. These pines produce large quantities of so-called specialized metabolites: terpenes, phenols, waxes, resins which are all antibiotic substances which will limit or even prevent the development of all these parasites or xylophages.
Slow growth
When you don’t have competition, you don’t need to push faster than the others and you can therefore save money, second golden rule.
The awned pine, which never reaches significant heights, is one of the tree species whose growth is the slowest!
There is no need here to have needles carrying out ultra-efficient photosynthesis: the awned pine retains these needles much longer than other pine species; they can remain on the tree for 20 to 30 years, whereas other pines change their needles every two or three years.
Twigs with cones © Thierry Gauquelin, CC BY-NC-ND (via The Conversation)
Of course, these very old needles, covered with dust, attacked by ozone, frost and the rays of the sun, will certainly be much less efficient than new ones, but this energy that the tree has not put into the production of new leaves, it can investing in specialized metabolism.
To economize is finally to limit its production of cones and seeds. When you have the millennium ahead of you, reproducing every year is useless. One or two windows of regeneration during a century are undoubtedly sufficient to ensure a renewal of the population.
Masters of frugality
Finally, it is necessary to be able to react in the face of disturbances, to adapt to them, because fortuitous events will not fail to happen during the 4000 years of a life which will not be a long calm river.
Thus, the sectorization of the conductive apparatus – the aerial parts of the tree being divided into different independent units respectively fed by different roots associated with them – found in the very old cliff junipers of the gorges of the Ardèche or the Verdon, makes it possible to survive following a partial destruction of the tree which has preserved only a very small part of the tissues carrying the sap.
Can these millennial trees inspire humans? In our modern societies, frugality, the harmonious distribution of space and the absence of competition are unfortunately out of place. And then, the human species does not benefit from the tens of millions of years of evolution that have forged the longevity of these pines!
This analysis was written by Thierry Gauquelin, professor emeritus at the Mediterranean Institute of Biodiversity and Marine and Continental Ecology of Aix-Marseille University.
The original article was published on the site of The Conversation.
