Alpharetta Specimen Tree and Replacement Calculator

If you are planning an addition, a pool, a new driveway or a teardown in Alpharetta, the big trees on your lot decide a lot about what you can build and what it costs. The City's tree conservation rules, in Article III, Section 3.2 of the Unified Development Code (UDC), protect specimen trees, set root-protection zones and require a minimum tree density on every developed lot. The City publishes a Guidance Document that explains the formulas in plain terms. The calculator below uses those formulas so you can estimate where you stand before you call an arborist or a designer.

What makes a tree a specimen tree

A specimen tree is one that qualifies for special consideration because of its size, type, condition, location or history, and that meets minimum size criteria. Specimen trees can be planted or landscape trees, and they do not need to be native (City of Alpharetta, Guidance Document for UDC §3.2). The size thresholds, measured as diameter at breast height (DBH, 4.5 feet above grade), are:

• Pines (Pinus): 30 inches or larger.
• Conifers such as deodar cedar or arborvitae: 20 inches or larger.
• Overstory sweetgum and tulip poplar: 30 inches or larger.
• Beech, tupelo, persimmon, sassafras, and Southern magnolia that reach over 40 feet: 20 inches or larger.
• All other overstory genera: 24 inches or larger.
• Understory trees, which mature under about 40 feet: 8 inches or larger; sourwood 10 inches or larger.

Size is not the only test. The tree must be assessed in fair, good or excellent health by a qualified professional using at least an ISA Level 2 assessment. Invasive vines, lean or co-dominant stems do not automatically disqualify a tree. The City also recognizes "trees of quality" and "tree groupings," which are treated like specimen trees for preservation credits; pine, yellow poplar, sweetgum, Bradford pear, Leyland cypress and invasive species cannot be trees of quality.

To measure DBH without special tools, the City suggests wrapping a string around the trunk at 4 feet 6 inches, measuring the circumference and dividing by 3.14. Forked trunks below 4.5 feet are measured at the narrowest point beneath the split.

Root zones: CRZ and SRP

The critical root zone (CRZ) is the area that must be left undisturbed to give a tree a reasonable chance of survival. Its radius in feet is 1.3 times the trunk diameter in inches, so a 20-inch tree has a 26-foot CRZ radius. An administrative variance may allow impact to the CRZ up to a 20% maximum. The structural root plate (SRP), the zone that keeps the tree from blowing over, has a radius of 0.5 feet per inch of DBH, and no impact to it is allowed (Guidance Document).

Trees on the neighbor's side of the line count too. If construction encroaches 10% or more into a boundary tree's CRZ, the tree's owner must be notified and proof of receipt provided before permits are issued. Above 20% encroachment, the City considers the tree lost, and an agreement signed by both owners is required. Notice never authorizes encroachment into a boundary tree's SRP.

Replacement density: 130 inches per acre

Every developed property must keep a minimum tree density. The standard formula is SDF − EDF = RDF. The site density factor (SDF) is the lot area in acres times 130 inches. The existing density factor (EDF) is the DBH, in inches, of the trees you keep. The difference is the replacement density factor (RDF): the caliper inches of new trees you must plant. The City's example: a 15,000-square-foot lot (0.34 acre) has an SDF of 44.2 inches. With no trees kept, that means 11 four-inch or 22 two-inch caliper trees. With two 15-inch trees kept, the RDF drops to 14.2 inches, or three 4-inch trees and one 2-inch tree (Guidance Document, Tree Density).

Detached single-family lots can instead use an alternate method based on 30% canopy coverage: site canopy coverage (lot square feet × 0.30) minus existing canopy kept equals the replacement canopy, using canopy values from the City Tree List. Replacement overstory and understory trees must be at least 2 inches in caliper. Replanting plans may include no more than 25% of any one genus, and more than 50% of planted trees must be native.

About "recompense"

UDC Section 3.2 also contains recompense provisions for removing specimen trees or trees removed without approval. We could not read the current ordinance text directly, because Municode would not load for us, so we do not state a multiplier or fee here. Read UDC Article III §3.2 on Municode or ask the City Arborist at (678) 297-6229 before you plan around a removal. Removing a live tree on a single-family lot requires a permit, and replacement trees may be required (City of Alpharetta, Tree Removal).

When you need an arborist report

An arborist report is how the specimen health test gets answered. It is also how a designer locates CRZs on a site plan. Alpharetta's individual-lot site plan checklist and stormwater handbook say the City reviews the CRZs of all specimen trees that encroach into your limits of disturbance, and any tree 6 inches or larger within 30 feet of those limits. Plan for a report early if a pool, addition or retaining wall is close to a large tree.

Sources: Angi, arborist cost; Angi, tree removal cost. Ranges are attributed to the publisher named; they are national or regional estimates compiled by that publisher, not quotes and not prices from any provider on this site. City permit fees are set by the City of Alpharetta, not by these publishers.

Local rules and code references

• City of Alpharetta, Guidance Document for UDC Article III §3.2: DBH, caliper, CRZ and SRP definitions, specimen thresholds, boundary trees, 130 in/acre density, 30% canopy method, replanting rules.
• Alpharetta UDC Article III §3.2 Tree Conservation (Municode): ordinance text, including recompense provisions.
• City of Alpharetta, Tree Removal: online permit application.
• City of Alpharetta, Stormwater Policy Handbook (Section 20): CRZ review of specimen trees and trees 6 inches and over within 30 feet of the limits of disturbance.

Code text, policy forms and department procedures change. Confirm current requirements with the jurisdiction, your insurer or the utility before work starts.