What would Princeton be without its trees? The blossoming pear trees on Witherspoon Street signal spring for many residents. Street trees provide shelter and shade that can save homeowners on air-conditioning and heating costs. 

According to Princeton’s Shade Tree Commission (STC), the U.S. Department of Agriculture estimates that the net cooling effect of a young, healthy tree is equivalent to 10 room-size air conditioners operating 20 hours a day. And if that were not enough, trees bring birdsong, give off oxygen, absorb carbon dioxide and pollutants, reduce storm runoff and the possibility of flooding.

The job of protecting and managing the town’s trees is overseen by the volunteers of the STC, working closely with municipal arborist Greg O’Neil.

The seven-member commission (with two alternates), appointed by the mayor and assisted by one municipal employee, has just announced the completion of an inventory of Princeton’s street trees. The inventory database, which can be consulted on the STC’s still-under-construction website (www.pbshadetree.org) will serve as a tool for Mr. O’Neil and inform decisions about tree maintenance, removal, and new plantings. It is also open to residents curious about the trees on the streets where they live.

“Anyone who has wondered what type of tree that magnificent specimen across the street is can go to the Shade Tree website and learn not only what species it is, but also its name, caliper, and estimated annual benefit,” said STC member Janet Stern. “Accompanying every tree is a Google map showing the site where the tree is located and an image of the tree.”

In addition to the location of each tree within the public right-of-way, the database provides size, condition, hazard rating, and maintenance needs. As yet, the database is confined to the street trees and does not include municipal parks and open space, trees on private property, or on state or county roads.

According to STC Chair Sharon Ainsworth, Princeton has a total of 18,558 street trees and at least 179 different species. The top ten species are in order of percentage: Ash (white & green) 10.97, Red Maple 9.6, White Pine 5.11, Pin Oak 4.43, Norway Maple 4.4, London Plane 4.15, Sugar Maple 4.11, Tulip Poplar 3.32, Norway Spruce 3.24, and Eastern Hemlock 3.19.

Diversity of species is important, said Ms. Ainsworth, because too heavy a reliance on a single species could have significant consequences should some disease or insect problem arise. “In neighboring states like Pennsylvania, the Emerald Ash Borer (EAB) is devastating the Ash tree population. To date the EAB hasn’t been found in New Jersey but if it does cross the river, it would create significant management challenges,” said the trained ornamental horticulturist who came to STC after serving with the New Jersey Department of Agriculture and as political liaison for Rutgers University for a combined period of 25 years.

As Ms. Ainsworth reports, most of Princeton’s street trees are deciduous and, as yet, it is too early to assess the full impact of this year’s winter storms. “Although structural damage, like broken limbs, is already apparent, damage to a tree’s overall health, for example from salt application to roads and sidewalks or from the severe cold, will take longer to become evident.”

Besides the new database, the STC website offers advice, including the best way to mulch a tree: mulch should be spread like a donut around the tree rather than packed up like a volcano; it should never be allowed to touch the tree’s bark, or piled higher than 3 to 4 inches; mulch that is too deep can promote fungal and bacterial diseases and wood chips or other coarse organic material are best.

Oldest Trees on Campus

Chances are, if you are a Princeton resident, you will have a favorite tree. Ms. Ainsworth has two, the massive gray-barked sycamores in front of the John Maclean House on Nassau Street, on the Princeton University campus.

Known as the “Stamp Act” trees, in commemoration of the repeal of the Stamp Act in 1776 around the time of their planting, they are well over 300 years old and are similar to London Planetrees, a sycamore hybrid.

As for the Witherspoon pear trees, Ms. Ainsworth looks forward to their blooming this month. “Pyrus calleryana are among the first to blossom but the exact date is difficult to predict because of changes in weather and temperature. The unusually cool temperatures have slowed bud development so they are behind where they would be in a typical year. One would expect the trees to be in bloom in early-mid April. The bloom can last a couple weeks, unless we go in the opposite direction and get summer-like temperatures.”

Arbor Day and Marquand Park

The Shade Tree Commission will celebrate Arbor Day on April 25, with a visit to Littlebrook School where a tree will be planted and small trees distributed.

The 60th anniversary of Princeton’s treasury of trees will be celebrated by the Marquand Park Foundation, Sunday, April 27, from 1 to 3 p.m. Mayor Liz Lempert will present a proclamation following remarks by Foundation Chair Pamela Machold, also a longtime STC member and by Mr. O’Neil.

At noon Roland Machold will lead a tour of the park and at 2 p.m., three new hybrid American chestnuts will be planted. A “Find a Tree” treasure hunt will take place at 2:30 p.m. A tent, chairs, and light refreshment will be provided.

Shade Tree Commission meetings are generally held on the fourth Tuesday of the month at 5:30 p.m. in the Monument Building (former Borough Hall). The next meeting will take place on April 22 at 5:30 p.m.