Calgary's erratic weather has stressed out more than the city's human occupants.

Arborist Matthew Davis says his clients have been concerned about the number of trees that haven't sprouted leaves or buds this spring.

"Fairly acute issues have affected different trees in different ways, but a lot of it relates back to a high-stress environment for the trees based on how the weather has been in Calgary the past number of years," Davis said.

Arborist Matthew Davis is busy with the pruning and assessing of stressed trees. (Monty Kruger/CBC)

The ups-and-downs of Calgary weather have impacted trees for a decade, Davis said, from the 2005 floods, an early frost in 2009, 2013's floods, so-called "Snowtember" in 2014, and several hot, dry summer seasons.

The "Snowtember" storm impacted 500,000 public trees and 1.5 million private trees, according to the city.

More than 24,000 trees were planted by the city as part of the recovery, but the city lost an estimated two to three per cent of its urban canopy in the disaster — something city officials estimated would take decades to fix.

Davis compares trees to people — if they don't get enough sleep or are under stress, their immune systems weaken.

"They become a lot more prone to invasion by insects and disease …They've been stressed out for almost a decade now."

The damage homeowners are seeing this spring dates back to the winter of 2016, as it takes a few years for damage to manifest, he said.

Heat can reduce a tree's ability to hydrate, as the pores on the bottom side of the leaves close up. As for extreme cold, a fast frost can cause water to get trapped in the tree, which as it freezes causes the trees' cells to explode.

Another concern is that Calgary is becoming an aging, established city.

"A lot of trees are hitting lifespan," Davis said, explaining that short-lived trees like birches are nearing the end of their 60- to 80-year lifecycle.

If a tree or branch hasn't begun to grow new leaves by mid-June, it's time to give up on those branches and prune them, Davis said, in order to keep the tree as healthy as possible.

Trees that have yet to sprout leaves by mid-June should be pruned, says Matthew Davis. (Monty Kruger/CBC)

"Any part of a tree that hasn't leafed out by this time of year is not going to produce going forward," he said.

He also suggested giving trees deep, infrequent watering to encourage drought resistance, and ensure they have the nutrients they need going forward, by ensuring trees have compost, fertilizer or mulch added to their soil.