The Plums are (nearly) ripe

I may be risking excommunication.

The landscape department, probably like many others across campus, has its share of secrets, little things nobody else knows about. My inside mole at the Grille keeps me updated when the linzertorte cookies are around. The view from the Bi-Hall roof after a snowstorm is spectacular. And, there’s a pretty spectacular plum tree on campus.

Plums are in the Rose family, the genus Prunus, which it shares with Cherries, Peaches, Apricots, and Almonds. The full latin name of the plum is Prunus domestica, The latin genus stolen from the greek word προῦνον (prounon), and the specicies domestica from the botanists term for “such a long and muddled history of hybridization we can’t possibly straighten it out”. It is no exaggeration to state that plums have been cultivated for thousands of years-Pliny the Elder writes of Apricots, stating them to be a type of plum, and a 6000 year old apricot pit was found in an archeological dig in Yerevan, the capital of Armenia. The earliest Prunus appear in the fossil record in the middle Eocene, about 45 million years ago.

Our plum is one of the first trees to bloom on campus, at about 80 degree days. In a good year, about 50% of the blossoms are pollinated, and bear fruit. Dry condidtions in the late spring will cause the fruit to drop while still small, and overly wet conditions are prime for Brown Mold, as unattractive as it sounds. Most plums are covered in a white waxy coating-this is a epicuticular wax that protects the fruit from UV light and also repels water.

There are many cultivars of plum. I’m betting, though, that our plum is a popular (and hardy, fortunately) variety known as Stanley. It’s a beautiful blue-purple color, with a golden meaty center, surrounded by a small pit. It was bred in the New York State Agricultural Experiment Station, part of Cornell University, located in Geneva. The station is  the mecca of hardy fruit hybridization, and brought us the Empire and Cortland apple. Stanley is literally the plum all others are now compared against. Richard Wellington developed the Stanley plum in 1926-when he started at the station, there was estimated to be 1 million plum trees in the state of New York.

Plums have a greater variety than other tree fruits, coming in many colors, sizes, sugar contents, and textures. They are an excellent source of anti-oxidants, more so than tomatoes, bannanas, apples and oranges. Marketeers are busy trying to sell us “dried plums”, hoping we forget grandmother’s name for them, the evil and dreaded prune. A sugar plum, aside from dancing in your head, is by law a plum with greater than 20% sugar content, at least according to the California Tree Fruit Agreement.

I enjoyed selling plum trees in my retail days. I was forever talking customers out of apples, as they aren’t really a tree as much as a pet, requiring greater care than anybody realizes. (Leave the apples to the experts-there is sanity in bulk) Plums, however, are carefree, without the serious pests and diseases of other tree fruits, and are self fertile, meaning one tree is all you need. Stanley should be hardy in most of the Champlain Valley, with perhaps the occasional late frost nipping the buds.

Oh yeah. I forgot to tell you where the tree is.

Lightning Strike

Our wild and crazy summer weather here at Middlebury continues, this time with a tree being struck by lightning. (Side note to the faithful readers out there. I feel for you-has this blog been getting depressing lately? With vandalism, more vandalismstorms, more storms, even still more storms, and disease,  it seems like the Middlebury Landscape is getting tragic. Hold the faith! We’ve been planting as well. Posts coming soon on this year’s tree plantings, as well as a new look for Pearson Hall.)

Ginkgo at 121 South Main

The tree hit is a Ginkgo ( read here if you’ve forgotten about them) located in front of one of Middlebury’s “outside” houses, near Public Safety at 121 South Main Street. I don’t know the night it got hit, but it was brought to my attention by one of the diligent members of our crew. Looking at the tree originally, I first thought the tree had just cracked down near the base, possibly in some strong wind. The tree shows what arborists call co-dominant trunks, where two trunks of equal size meet and grow together. This is frequently a recipe for disaster, as a bad union often results, where included bark makes a weak joint, and the two trunks typically fall apart away from each other.

Co-Dominant Trunks-click for a larger view to see the wound

I called an Arborist friend to consult on the damage-this is one of our favorite trees in Facilities, many of us would mourn the loss. His skill, knowledge, and experience led him to look up the tree, rather than me just jumping to the first obvious conclusion, and that was how he discovered the damage around the cable up top, as well as noticing the toothpick sized wood pieces scattered around the yard, small pieces of trunk blown away from the tree from the force of the lightning. Being tree geeks, we climbed up to investigate.

Damage around one the cables

Damage on another limb-the lightning jumped to this branch

Trees are frequent targets of lightning. Standing alone, frequently taller than many buildings around them, many trees get hit each year. Lightning is fascinating all on it’s own, with their impressive 100 million volts and  temperatures greater than 50,000 degrees fahrenheit. 16 million lightning storms are estimated worldwide in a year, and measuring instruments record over 100 million strikes in the U.S. each year, killing on average 90 people. They even get their own phobia, Astraphobia, fear of lightning.

The conditions needed for lightning are still debatable, but should those conditions exist, negative ions accumulate at the base of the storm clouds, while positive ions pile up on the ground. “Stepped Ladders” descend from the clouds, while “streamers” arise from the earth, typically strongest from the tallest structures, such as buildings or trees. Should they build strong and fast enough, they meet to form a lightning bolt, and this electrical discharge super heats the air around it to 36,000 degrees fahrenheit, compressing the air creating supersonic shock wave we hear as thunder.

When lightning strikes a tree, the sap in the tree boils, turning to steam and blasting the bark away from the trunk. The electrical charge flows through the tree, exiting out the root system, which could be severely damaged in the process, sometimes with no visible sign above. In most cases, though, a strip of bark is torn from the tree, often in a long strip, but sometimes, like this ginkgo, only above and below. Trees with only one crack tend to close the wound and suffer, yet live, while trees with wounds on both sides of the trunk are frequently killed outright. Obviously, even a wounded tree can die from secondary reasons, such as insects and diseases, less able to fight them off.

Trees vary in their susceptibility to lightning strikes, possibly for biological reasons, or possibly simply because of their height. Elms, Oaks, Black Locust and Ash tend to be very susceptible, while Beech, Horsechestnut, and Birch tend to not be very susceptible. It may be the starch content of the tree making it more susceptible, while resinous trees are poorer conductors.

So there is hope for our Ginkgo. The wound at the bottom was traced, where loose bark is peeled away carefully from the trunk to the point where it attaches again. The thinking with bark tracing is that loose bark can trap moisture and disease, so by removing it the wound can dry better. Maybe it’s just something to do to make arborists feel not quite so helpless…

Lower wound after tracing

Lower part of wound where lightning went to ground

The cabling up in the crown of the tree is a little more problematic. Originally put in place to help stabilize the two co-dominant stems, the system now obviously cannot be trusted, as the wood surrounding the bolts holding the cable is now dead. We decided to replace the cable with two others, one above the old cable (a better location from an engineering perspective), but also one looser below, in case one of the stems fails completely at the original cable site, and breaks. The tree will then still be braced by the lower cable.

Placing the cables in the tree

The three cables in place

So now, we wait. The rest of this year, and into next spring, will be the crucial time, and when we shall see just how bad the strike was. Should it still appear somewhat healthy next spring, we will aerate the soil around the tree, add compost, fertilize, and mulch. Hard to imagine now, but, if we get a little drought this summer, we’ll even go down to water.