2007-06-16 / Columnists

Nature Notes

Could Popular Legend of 300-Year-Old Lilacs on Mackinac Be True?
By Patricia Martin

This past week has been the annual "Lilac Festival" here on Mackinac. The festival has been going on since 1949, and was established to encourage people to come and enjoy our beautiful lilacs. Mackinac has more than 100 varieties of the Common Lilac (Syringa vulgaris), which are sometimes referred to as French Lilacs, as many of the popular, early hybrids were developed in France. There also are several other species of lilacs here. Lilacs grow well and quite rapidly on the Island, perhaps owing to our climate, but particularly owing to the limestone that makes the bedrock of Mackinac. We have some of the largest trees (and because of the way they grow, we call them trees, not shrubs) in the country, some with diameters of more than two feet.

There is one question that has long plagued us, and that is, "How old are the lilacs?" Lilacs are not native to North America and so had to be imported. For years, stories have circulated that the lilacs were brought to the area by the French missionaries and settlers, the first of whom arrived on the Island in 1669. If this was the case, the lilacs could be more than 300 years old. One problem with this theory is that the Jesuit mission that was established on Mackinac lasted only one year on the Island before moving to St. Ignace. I personally have a difficult time imagining Father Marquette paddling into the Straits carrying a lilac rather than a cross. No record of lilacs has yet been found to support this theory of early arrival of lilacs in the Straits area, but we do know that lilacs were introduced to North America during the Colonial period, and that Jefferson and Washington both had them in their gardens. Perhaps the reason the story of the 300-year-old lilacs arose is because of the large size of the trees, and the fact that many people refer to them as French lilacs.

Charles Holetich collects a bore sample of one of Mackinac Island's large lilacs to determine its age. Charles Holetich collects a bore sample of one of Mackinac Island's large lilacs to determine its age. It's much more likely that the lilacs arrived on the Island after the pertinent settlement was established during the Revolutionary War by the British in 1779-1780. This could still make the lilacs more than 200 years old. A friend of mine, Brian Dunnigan, has been researching the early journals of people who came to Mackinac for an upcoming book, and has found no mention of these plants. The first reference to lilacs occurs when Gurden Hubbard named the cottage he built in the Annex in 1870 "The Lilacs." He came from Vermont, and his family apparently raised lilacs. Whether he brought lilacs to the Island is unknown.

Charles Holetich finds the diameter and radius of a lilac to help determine its age. Charles Holetich finds the diameter and radius of a lilac to help determine its age. Last week, when the International Lilac Society met at Mackinac, I had the privilege to meet and work with three members of the Society, Charles D. Holetich, Dr. Zilimir Borzan, and Vreek Vrugtman, who were trying to age some of the lilacs on the Island. These three gentlemen, all originally from Croatia, have spent years studying and working with lilacs. Mr. Holetich created the world's most diverse public lilac collection at the Royal Botanical Gardens in Hamilton, Ontario. Mr. Vrugtman is the world registrar for the genus Syringa (lilacs).

The method used in this process is one used commonly in aging trees. It involved taking a small bore sample, several inches long, from a large lilac trunk or main branch about two feet above the ground. The sample itself is only about an eighth of an inch in diameter. The annual growth rings in the sample are counted, and using ratio and proportion and the radius of the tree, the number of annual rings are then calculated for the whole trunk. This method has about a 2% margin of error. This gives us the age of that stem at that height (two feet) above the ground. On average, it takes about two years' growth for a lilac to reach that height, so two years are added to the number of annual rings. This only tells us the age of that branch or trunk. If there are older stems that have died and are no longer present (lilacs often have multiple stems), we have no way to tell exactly how old the whole plant is. After the samples are taken, the small bore hole is plugged so that insects or diseases can not get in. The hole will heal over in a year or so.

In the study we conducted last week, I got permission from a number of people who had large lilacs to test their trees, and Mr. Holetich selected the best ones for our purposes. (The project was successful thanks to all who allowed us to use the lilacs). Four trees were chosen, though only three gave viable results, as one of them was rotten on the inside. The results are as follows: Sample 1 (the largest tree sampled) had an 18.5-inch diameter and a radius of 9.25 inches. A bore was taken 2.62 inches long, which contained 24 annual rings (years). Doing the calculations 24 years/2.62 inches = 9.16 years/inch. If you multiply the 9.16 years/inch by the radius (9.25 inches), you arrive at a calculation of 84.7 years, to which you then add two years for the stem to reach the height of two feet, to get a grand total for that stem of 87 years.

We did a similar calculation for Sample 2, which had a radius of 8.75 inches with a bore sample 3.5 inches long, with 36 annual rings in it, and came up with a ratio of 10.29 years/inch. Finishing the calculation, that particular sample came up to be 92 years old.

The third was the smallest sample with a radius of 6.25 inches, which had a ratio of 9.87 years/inch, aging this tree at 64 years.

One could make a rough estimate of the age of other Island lilacs by averaging the years/inch of these three samples and multiplying that by the tree radius. That is 9.16 years/inch + 10.29 years/inch + 9.87 years/inch = 29.32 divided by three (the number of samples), which would equal 9.8 years/inch of radius. This means if we took the radius of one of the largest of Mackinac's lilacs, which is 12.5 inches at two feet above the ground, by this method we could calculate the age to be about 125 years old.

Sorry, folks, we're not finding any 300-year-old lilacs. I guess we must be happy with some of the largest lilacs in the country, not necessarily the oldest, though 125 years is nothing to sneeze at, and it's pretty close to the earliest mention of lilacs on Mackinac.

One more step I would like to take in dealing with the age of lilacs, would be to take a three-inch cross-section of one of the large lilacs that was cut down last year, measure its radius, polish it up so the annual rings could all be counted, and find out its age. It might also be possible to place it on display in one of the local museums or public buildings, so that people could see the age and the rings for themselves.

Trish Martin is a yeararound resident of Mackinac Island, has earned a master's degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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