Health AND SURVIVAL OF BEECHES AND OTHER ANCIENT TREES
by Ruth S. Foster
Perhaps one reason Winslow Homer's beeches thrived is because no one mucked around with them over the years. They were left alone to grow naturally and slowly in the historic district. Their root run was protected from construction, herbicides, new sod and the ministrations of grass perfectionists. No fancy landscape pruning or repeated fertilizing was done, just some structural pruning and cabling. And they are probably over an underground stream.
WHY DO CERTAIN TREES LIVE TO BE CENTURIES OLD?
The fascination of these old trees is why have they survived when the average life span of a tree is a mere 40 years? Four factors are most important.
.... FIRST is their genetic makeup; some species are long lived, others are not.
.... SECOND, these giants probably have tapped into a reliable underground water source. At Chenenceaux, they grow along deep drainage ditches. The Romans always chose sites with a pure water spring, which happens to run next to the row of old trees in Villaneuve. The trees on Memorial Drive send their long thirsty roots into the adjacent Charles River.
.... THIRD, they were not abused by man nor beast. Farming, foraging and wildlife were the main hazards of the past. Construction damage and changing the root environment are the main risks today.
.... FOURTH is the weather. Old trees are very heavy and so very subject to wind damage. Pruning and cabling can help. Droughts take their toll and climate change as well. A deep watering, once a month, during periods of low rainfall helps. What's deep? Leave a sprinkler on the root run at least overnight.
CARE OF ANCIENT TREES
Keeping old trees growing for another century requires understanding what care they need, as well as what not to do. Old trees have to grow very slowly, just enough to survive.
Dennis Collins, Curator of the Plant Collection at the Mount Auburn Cemetery, first planted in 1831, feels that "in most cases, a tree can grow indefinitely. Then simply some change in its environment such as climate, storms, pathogens, soil chemistry, construction, grass under the dripline will stress the tree. Often it's a combination of stresses."
When trees are abused or seriously stressed, they go into decline and die. However, they die very slowly. So to identify the cause usually means thinking back to what happened several years ago. For instance, was a new driveway installed, or curbs, or sewers? Was sod put on top, or herbicides, strong fertilizers or a new sprinkler system?
WHAT'S SOME OF THE SCIENTIFIC THINKING?
AT Harvard's Arnold Arboretum, they test the soil pH to a depth of 18-24 inches and often find it's more acid (pH 5) than most trees prefer, especially their old beeches. So they are using dolomite lime to raise the pH under species that prefer it closer to 6.
They are now realizing the importance of the soil and its microbiotic soup of tiny organisms that are necessary to facilitate the uptake of nutrients and soil needs organic material to nourish them. So it's back to them old basics. (The current fad label is "green" or "organic", but neither is accurate.)
Basic to improving the soil is mulching which increases the numbers of these anonymous live creatures in the soil. Best are well rotted wood chips. How long is well-rotted? About 9 months to a year, depending on the time of year, (faster in warm climates) but beware of incomplete decomposition.
Under beech trees, however, the best mulch is their own leaves left on the soil in a circle under the dripline of the trees. They enhance and replicate the specific microbiotic soup of organisms that beeches must have. And never, never use herbicides!
Thomas Ward of the Arnold Arboretum said that after a year under mulch, the soil becomes full of earthworms, who in turn deposit their castings, the ultimate organic, to enrich the soil.
Another observation at the Arboretum is that given optimal growing conditions, some trees grow too fast, may not allocate their resources well, and perhaps use up their life span too soon. For example, trees like their 80 year old sugar maple (18 inches diameter, 70 feet high and wide). The question is how will these tolerate past years of recurrent drought, and especially the temperature shifts from climate change.
So what is the documented oldest tree in Harvard's Arnold Arboretum, founded in 1872? Actually it is a 1737 Chamycyparis obtusa in their bonsai collection. It grows slowly, slowly, constantly pruned and pampered. And it grows in a pot.
AT THE Mount Auburn Cemetery, they had serious problems with their many old beeches in the 1980's. They instituted a program to improve their health. They removed the turf from under the dripline. (the farthest reach of the branch tips).
Then they added an organic supplement (emulsified seaweed, which has a growth hormone) topped with some inches of wood chip mulch. Also water during dry periods. Slowly, their health and vigor improved.
THE PRINCE OF WALES BEECH TREE
One important beech, planted by the Prince of Wales in 1860 suffered from badly compacted soil. In that case, thin radial trenches, 24 inches deep, filled with stone were added to all of the above. Collins says, "It's improved but not yet out of the woods."
He feels the worst thing under an old tree is a turf. It competes with the roots in every way possible. The best thing for any tree is the largest possible area of mulched leaves. And the most important thing for preserving an old tree is a few regular deep waterings during extended drought periods.
Interestingly, Mount Auburn Cemetery's Japanese maples have done quite well. They have the state champion planted in 1910 (24 inches diameter, 50 feet tall). However it's planted in a protected hollow sheltered from hurricane force winds.