A City That Measures Its Own Tree Canopy Every Two Years

Most cities have opinions about their trees. This one has a time series.

The measurement

The City of Sandy Springs publishes a tree canopy record through its Urban Forestry Program, and it has evaluated canopy every two years since 2013. The figures it publishes by pixel classification run 58.7 percent in 2013, 58.5 in 2015, 60.3 in 2017, and 58.1 in both 2019 and 2021. From 2017 it also publishes an AI-derived series: 56.5 percent in 2017, 55.0 in 2021 and 54.5 in 2023, the most recent published figure.

The two series are not directly comparable, which the city itself flags, so the honest way to read it is within each method rather than across them. Read that way, the direction is gently downward.

The city has planted more than 3,000 trees since 2018. It has been recognised as a Tree City USA by the Arbor Day Foundation over a long run of consecutive years, and as one of the Tree Cities of the World.

Why a homeowner should care

Because that measurement is the reason the ordinance has the thresholds it does, and the thresholds are the reason a landscape project here takes a shape it would not take in a neighbouring city.

A tree removal permit is required in Sandy Springs for any tree measuring 18 inches diameter at breast height or larger, for any dogwood or redbud at 10 inches or larger, and for any tree inside a stream buffer or the Chattahoochee River Corridor at any size. Where removal is associated with construction activity such as grading, a pool, a patio or an addition, the submittal is a Tree Conservation Plan under Division 9.3 of the Development Code rather than a simple removal permit, and it goes in with the construction drawings.

The city also runs a Tree Fund. Among its uses is financial assistance for preserving significant trees on private land, with eligibility set at hardwoods of 27 inches diameter at breast height or more and pines of 30 inches or more, a documented health or safety concern with potential for recovery, a maintenance plan from an ISA Certified Arborist, and a mandatory three-year protective covenant over the tree’s critical root zone.

The design consequence

On a lot in a city with 54.5 percent canopy, the mature trees are a fixed input rather than a variable. That has three effects on a landscape plan.

The plant palette is settled before it is chosen. Everything under a closed canopy has to be a shade plant. UGA Extension puts the practical floor for turfgrass at around four hours of full to filtered sun a day, which large parts of a wooded Sandy Springs yard do not reach in July.

Hard surfaces get located around root zones. Compacting a base over the roots of a mature tree causes decline that appears years later, and the tree that then has to come out is a permit as well as a canopy loss. Moving a patio a few feet is cheaper than every alternative.

Grade cannot rise over a tree. Raising soil level over a root zone buries the root flare and cuts oxygen to the roots. It is the most common way a mature hardwood is lost during a landscape project, and it is entirely avoidable.

The thing worth noticing about the trend

A canopy that drifts downward by a fraction of a percent every couple of years is not a crisis and it is not nothing. It is the aggregate of individual lots losing individual trees, most of them not to chainsaws but to slow decline that started with something done nearby.

Which means the highest-value contribution a single property can make is unglamorous: keep the grade where it is, keep machinery off the root zones, get the ivy off the trunks, and have somebody competent look at the mature stems before designing anything around them. None of that is expensive and all of it takes decades to undo.

More on working under an established canopy in the shade planting guide, and on the permit thresholds in the tree rules guide.

Sources: City of Sandy Springs Urban Forestry Program canopy figures, Tree Removal Permits page, Tree Fund page, and the Tree Conservation Ordinance at Division 9.3 of the Development Code. UGA Extension Bulletin 1533-1.