Paleobotany - Just how old is old?
In the summer of 1968 I was working for the U.S. Forest Service in southeast Alaska, cruising potential timber sales. During these trips to the various islands, I came across active logging sites with the proliferation of freshly cut stumps. The growth rings on these stumps made me wonder just how old these “old growth” forests were.
Living Trees
Sitka Spruce and Western Hemlock
In the spring of 1968 I had been on a forestry field trip to northern California and Oregon and saw everything from giant redwoods to slow growing ponderosa pine. A cross section of a ponderosa pine at one of the Forest Service buildings pointed out the fact that this tree began growing before Columbus set sail from Spain. Wow!!
When I counted the growth rings of the Sitka spruce and Western hemlock in Alaska, I was disappointed to find out that they were a mere 150 years old, plus or minus 15 years. This was an even-aged stand of timber that regenerated after a large die off of the original timber. Even at this “young” age the hemlock was beginning to suffer from rot and the stand was in decline.
Eastern Red Cedar
I grew up in the unglaciated region of northeast Iowa and southeastern Minnesota. Due to the lack of glaciation (the technical term for this is a “nunatak” area), the region is quite rough and hilly. Large sandstone bluffs overlook much of the area which is very picturesque when one floats down the Mississippi river on a summer day. Along these bluffs grow Eastern red cedar trees…barely clinging to life as their roots try to pry moisture and nutrients from the sandstone outcroppings. Recently I cut a cross section from a dead cedar growing on the edge of a precipice. (These small, gnarly trees are known by the German word krumholtz.) The growth rings were so close together that it was extremely hard to determine its age, even with a magnifying glass. Simple math gave me a rough figure of 150 years of age. However, some of these trees have been found to be over 500 years old. They grow slowly with very little photosynthetic area and thus, can survive for hundreds of years with little moisture and nutrients.
Bristlecone Pine
Another type of vegetation that grows in a very demanding environment is the bristlecone pine located in various areas of California and Nevada. This trees species has been found to have lived a precarious life in the harsh mountains for some 5,000 years. By cross checking dead trees lying about the area, a chronology of tree ring dating has gone back some 7,100 years. When trees grow alone in the absence of any other vegetative competition, the only factor that will limit their growth is moisture. Thus, one can get insight into the climate in that area spanning thousands of years. This is important data for climatologists and glaciologists. Archeologists use tree ring data to date timbers found in ancient dwellings in the Southwest and can accurately determine when a certain building was constructed.
Sagebrush
In the dry western United States, sagebrush dominates the landscape as it needs very little moisture to survive. The big sagebrush (Artemisia tridentata) is the major player in these dry areas. Many of these specimens are 100 years old and they too can lend insight into drought conditions for a particular area.
Sequoia
The giant sequoia of California is not only very large, but very old. Specimens have been found that precede the birth of Christ by a thousand years. The redwood tree also tops the list of trees that can live to a ripe old age. These trees reside in an area with excellent growing conditions including fog and its resultant moisture. Redwoods are quite impervious to rot and fire and can continue to grow with few pathogens to worry about.
Fossilized Trees
So much for the age of living trees. What about those dead trees that are entombed in the muck and rivers of the world. We are not talking about petrified specimens that have been turned to stone, but wood that has been preserved in an environment not conducive to rot.
The Fossil Trees of Axel Heiberg Island
On Axel Heiberg Island west of Greenland, a forest has been found that has been buried for 45 million years in the mud of that cold environment. The trees in this forest once grew to be 150 feet tall and lived to be 1,000 years old. However, the existing climate changed and they died and were buried. For 45 million years they lay where they fell, covered in sediment and waiting to be discovered. Remember, these trees are not petrified, but are still real wood that one of the researchers probably used to brew his coffee. There are many layers of trees and tree stumps in this location and some were able to be identified as dawn redwoods even though over the fallen tree trunks of an earlier forest, a new forest grew up.
The Terminal Moraine called Long Island New York
When the glaciers retreated from the northeastern United States, they left behind a terminal moraine which is now known as Long Island, New York. Another remnant of this glacial retreat was a lake located north of New Haven, Connecticut. As the area became forest once again, dead trees, leaves, butternuts and beech nuts floated into the lake and were buried. Clay washed into the lake and settled to the bottom covering the dead vegetation. With little oxygen, a wet environment, and a low temperature, this organic matter survived without rotting. There it lay until the area was eventually mined for the clay to manufacture bricks. As these remnants of a distant time came to life, people wondered just how old they were.
A scientific tool known as radio carbon dating solved this puzzle.
- Some of the oldest specimens uncovered in the pit were sycamore, which were carbon dated to some 6,200 years before the present.
- The author has a cross section of an oak specimen that died 4250 years before the present.
- An Eastern hemlock was dated to 1,250 years ago and was in such excellent shape that the author could tell how it grew and died. (There will be more on this in a later article.)
- The beech nuts were so well preserved that when they dried out, they opened up as if to drop their seeds.
- The author of this article stabilized a section of sycamore and made a gun stock from it.
Alas, civilization kept marching on and now this paleo-biological laboratory is a dump for used tires.
Various tree species entered the landscape at different times in the evolutionary path of the earth. As the climate changed on the planet, some species became extinct and new species adapted and proliferated. Two interesting species that have survived for millions of years are the ginkgo and the dawn redwood.
Ginko Biloba
There is one species of ginkgo that now remains and that is Ginkgo bilboa. It has been cultivated for centuries in China and Japan and is used for temple gardens. It is now used extensively in the United States as an ornamental tree and has has attained heights of nearly 100 feet and 27 feet in circumference. One specimen has even reached the ripe old age of 1200 years. The point of this article is that the ginkgo has been identified from fossil records from the Tertiary period, or about 60 million years ago. It is remarkable that it still survives after all of these millions of years and in the same form.
Dawn Redwood
The other interesting tree species is the dawn redwood (Metasequoia glyptostroboides) that has been found in the fossil record from the Mesozoic Era. It was a great surprise to the scientific community when a grove of Metasequoia was discovered in China during WWII. After the war the species was studied in its natural state and in 1948, Harvard brought some of the seed to the United States for propagation and study. It has been planted in various parts of the United States and makes a beautiful ornamental planting. Unfortunately, man may be the final arbiter in its survival after all of these millions of years. Illegal seed collecting in China threatens the regeneration of this small stand of natural dawn redwood in China.
Now that you have read this article you may never look at a tree in the same way again…whether it is large or small. When you see a lone tree growing along a water course in the Great Plains, you just might wonder what that tree has experienced as it kept its lonely vigil on what appears to be a desolate landscape. Did it hear the rumble of mighty herds of bison a hundreds of years ago? Did the gnarled oak in the heartland feel the weight of thousands of passenger pigeons on its mighty limbs? Did the small, twisted Eastern red cedar growing on the bluffs of northeast Iowa see the boats of early explorers ply the Mississippi river, or hear the final cannon shots at the Battle of Bad Axe when Chief Black Hawk was defeated and his land taken away for one last time? I hope that I have piqued your interest in this small treatise on paleobotony!