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 recognized 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 54.5 percent canopy means the average yard in this city is a woodland floor with a house on it, and almost nothing written about residential landscaping assumes that starting point.

A number that size changes what the constraint is. In an open suburb the limiting factor on a planting plan is usually water or soil. Here it is light, and light is the one input a homeowner cannot buy more of without giving up the thing that made the lot worth buying. Everything else in a design follows from that, which is why counting hours of sun in leaf-on conditions is worth more than any amount of guessing from a winter walk.

It also explains why so many yards here are running a losing argument with a lawn. A lawn planted when the neighborhood was new sits under a canopy that has been closing over it for thirty years, and turf declines gradually enough that the thinning reads as a maintenance problem rather than a light problem.

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, by which point the patio is finished and the tree is a removal bill. 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 choosing a grass for what light is left in the lawn guide.

Sources: City of Sandy Springs Urban Forestry Program canopy figures. UGA Extension Bulletin 1533-1 for the turfgrass shade ratings and the four-hour minimum.