Inventory counts city’s trees, charts condition, evaluates role

As long as there have been cities, people have planted trees along streets, in parks and in yards.

To better assess how Spokane street trees contribute to the city’s infrastructure and to attempt to put a dollar amount on the role the trees play – such as storm water mitigation – the Davey Resource Group has been hired to do a citywide street tree inventory.

“This is not about taking down trees,” said Angel Spell, Spokane Parks and Recreation Department’s urban forester who is overseeing the effort. “Actually, one thing the inventory will allow us to do is to identify good planting locations for new trees.”

The counting crews carry electronic tablets on which they register the trees. They have started counting in the West Central Neighborhood and are expected to have inventoried the entire city by Nov. 15.

Each tree in the city’s right-of-way will be located by GPS, have its trunk circumference and height measured, be properly identified and be assigned a score that reflects its condition.

“They also note any defects, like decay or a trunk scar or whether the tree needs pruning. And they note how the tree interacts with its surrounding space,” Spell said. All that information will then be recorded in the city’s geographical information system.

The city is using stormwater management funds to pay for the count, which is not to exceed $250,000.

One outcome from the inventory will be in locating new planting areas and neighborhoods where swales, like the newer ones on South Lincoln Street, might be considered for stormwater management.

“It’s important to stop the stormwater runoff before it hits the river or the wastewater treatment plant,” said Spell, explaining that in some South Hill neighborhoods stormwater runs into the normal sewer line and floods the system during heavy rains, resulting in sewage overflow into the river. “Trees would let us treat stormwater on site, instead of sending it into the river.”

Another outcome will be an assessment of the energy savings trees provide by shading homes in the summer.

“We will be able to put a dollar amount on that,” Spell said, “and the same goes for air quality and water quality benefits provided by trees.”

The inventory also will show which trees thrive as street trees in Spokane and which don’t.

“The most common trees are not necessarily the ones that are the best-performing street trees,” Spell said.

The most common urban trees are Norway maples and London planes – the latter is commonly called a sycamore. Knowing which tree specimen performs the best with the least maintenance makes a huge difference when people are picking trees for new plantings.

“And of course there are a lot of ponderosa pines, but they tend to be mostly in people’s yards,” Spell said.

The inventory will show which trees don’t function in their surroundings – perhaps they push up sidewalks or tangle with overhead power lines – and which are affected by disease or weakened from dieback and poor pruning.

“The property owner is responsible for the maintenance of the street tree, just like he’s responsible for maintaining the sidewalk,” Spell said. “We are happy to come out and give advice on how to tackle these situations.” Sidewalks can be rebuilt over tree roots and in some situations curbs can be moved to make room for expanding tree trunks.

The bottom line is that the inventory is about better urban forest management, not about removing trees, Spell said.

“We do not want to remove a tree that’s functional in its location.”