Finding out the age of the Officers' Square elms after Fredericton city officials announced plans to cut them down turned out to be more complicated than expected.

If unharmed by Dutch elm disease, the trees can live up to 250 years. The three largest elms in Officers' Square stand tall with straight trunks. Their branches fall in an umbrella shape - shooting up in pillars and arching at the top.

Amid controversy about the city's now suspended plan to cut down 19 trees in the square, protesters defended the trees because of their age, calling them historic or irreplaceable.

But size alone can't determine age and the city doesn't have a record. The only way to estimate age by sight is by using archived photos to compare to the modern landscape.

Above, this comparison from the 1887 floods shows that the elm tree in front of the barracks did not exist at that time.

The elm expert

Ed Czerwinski, an instructor of urban forestry at University of New Brunswick and a member of the city's tree commission, has taken his class downtown and studied many of the trees there.

In 2014, his class compiled a report specific to the Officers' Square trees. While he doesn't know the ages of these trees, his class compiled a rough estimate.

He knows the area by heart, and can recognize younger versions of the trees, so with the help of the Provincial Archives of New Brunswick, he was able to cross-reference photographs from as long ago as the 1870s to see if the estimates are even close.

This elm tree on the north edge of the square may be 140 years old. (Hadeel Ibrahim/CBC)

The elms

His class listed three of the oldest and largest elms as 150 years old.

Czerwinski said in Officers' Square there are seven elm trees, two of which are over 100 centimetres in diameter. Two are under 10 centimetres in diameter and "have no intrinsic value other than they've been replaced recently and could be easily replaced."

The two largest ones are likely the two oldest.

After reviewing 10 photographs from different dates and angles, he said almost all trees in Officers' Square are younger than 135 years old.

There is one exception, a tall elm on the river-side edge of the square. It stands closest to the change house.

There is a trace of its trunk in a photo of the barracks from the 1870s. The small trunk peeks from behind a larger tree in the foreground. The trunk is straight and thin, much like the straight, but much thicker, trunk of the tree standing now.

That one may be more than 145 years old.

"That's probably the largest elm in diameter that looks like it may be the same shape," Czerwinski said.

The second oldest

This may be the most conclusive evidence he has found.

This photograph, below, from 1939-42 shows a lanky version of the large elm standing in front of the barracks

Czerwinski said that photo shows a tree that may be around 30 years of age. Doing the math puts this elm at just over a 100 years old.

The elm standing in front of the barracks may be 110 years old (Hadeel Ibrahim/CBC)

The mystery elm

The third largest elm stands at the corner of Regent and Queen Streets. Czerwinski's students estimated the tree's age to be 150 years old. The photographs from the provincial archives did not include it.

The rest of the trees in the square are all quite young, ranging in age from eight to 50, but most are estimates.

Complicating factors

This method is less than scientific. Size comparisons are more complicated because the area where the trees are growing is a fertile floodplain.

"The Saint John River Valley system, we have that flooding that occurs, which we dislike from one point but it brings nutrients from these flood plains," he said. "We're able to grow trees very well here."

He said the photos show how big a tree can grow in less than 100 years.

"We have great heat in the summer, lots of moisture, all of which is very important," he said,

A better way to know

Czerwinski said there is one other way to know the ages without hurting the trees too much. It's called an increment borer, which will cut a one-eighth inch core.

It takes about a year for the trees to heal from the procedure. Czerwinski said it's a common way to count the rings in the tree's trunk.

The CBC asked the city for permission to conduct the test, but did not receive a response before deadline.