How Austin's Heritage Tree Ordinance Shapes What Gets Built
On the morning of Texas Independence Day, 1989, city forester John Giedraitis walked up to a 500-year-old live oak at 507 Baylor Street and saw a ring of dead grass around the trunk. Someone had poured Velpar around the roots of the tree Austinites called the Treaty Oak, enough herbicide to kill a hundred trees.
The poisoner, a farmworker named Paul Stedman Cullen, got nine years in prison and a $1,000 fine from Judge Bob Perkins. A 22-arborist task force flew in from across the country. H. Ross Perot wrote a blank check for the recovery.
About a third of the tree lived. It's still standing.
Thirty-one years later, in August 2020, the owners of a small house at 1711 Waterston Avenue in Clarksville sat in front of the Board of Adjustment asking for three variances at once: a side setback cut from 5 feet to 3.5, an impervious cover (IC) bump from 40 percent to 44, and an IC limit bump from 45 to 49.
Their architect, Ryan Bollom, told the board what the design was actually doing. "This design proposal is trying to preserve their neighbors' trees." Twelve trees ringed the lot. Ten of them belonged to other people.
The board approved all three variances. Unanimously.
Different decades, one consistent fact about Austin. On many lots in this city, the heritage tree ordinance shapes a site plan as much as the zoning does, and sometimes earlier in the process.
A single mature oak, pecan, or cedar elm above 24 inches at the trunk creates a protected area that grows as the trunk grows: one foot of protected radius for every inch of diameter. The circle applies even when the trunk itself sits on a neighbor's property. Cutting one down requires a city variance, and the replacement obligation is three trees of equal caliper for every one removed.
On many Austin lots, the trees are one of the first constraints a site plan has to honor, alongside the setbacks rather than after them.
What counts as a heritage tree
The plain-English rule is short. Twenty-four inches at the trunk, measured at four and a half feet off the ground (that's "diameter at breast height," or DBH), and one of ten species.
That's it. Texas Ash. Bald Cypress. American Elm. Cedar Elm. Texas Madrone. Bigtooth Maple. Every oak, meaning every species in the genus Quercus. Pecan. Arizona Walnut. Eastern Black Walnut (Austin Land Development Code § 25-8-602(1)).
A 24-inch live oak is a heritage tree. A 24-inch sycamore is not. A 23.9-inch oak is not. The code rounds half-inches down, so a measurement between 23.5 and 23.99 is recorded as 23.5 and stays below the threshold (Environmental Criteria Manual § 3.3.2.A.2).
The City Arborist re-measures contested cases. The line is exact and the rounding favors the developer by a hair, but the species list does the heavy lifting. In Austin, where the urban canopy is mostly live oak and pecan, the species list catches almost everything mature.
The 24-inch threshold sounds generous until you see one in person. A 24-inch live oak is roughly the size of the tree in a 1950s front yard photo.
It is not rare. On a wooded East Austin lot, a tree survey often turns up two or three. On a Hyde Park lot, often more.
The circle nobody draws on the zoning map
The number that runs the rule is the Critical Root Zone (CRZ). One foot of radius for every inch of trunk diameter (ECM § 3.5.2.A.1).
A 24-inch tree has a 24-foot CRZ. A 36-inch tree has a 36-foot CRZ. A 50-inch tree has a 50-foot CRZ.
Stand under one of the big ones on West 24th and look up. The circle goes out to the dripline and a few feet past it.
What the city protects inside that circle isn't the tree. It's the dirt.
The roots that keep the tree alive don't dive. They spread sideways in the top three feet of soil, looking for water.
Compact that soil with a backhoe, pour a slab over it, or pile fill on top, and the roots die. The tree dies eighteen months later, and by then the contractor's gone.
So the code defines preservation by what you can't do inside the circle. At least 50 percent of the CRZ area has to stay at natural grade. The entire inner half of the circle, what the code calls the Half CRZ, has to be protected. No cut and no fill is allowed anywhere inside the Quarter CRZ, the innermost ring (ECM § 3.5.2.A).
A tree marked "to remain" on a plan that fails any of these tests is not preserved. It counts as removed, and the developer owes full mitigation as if they'd cut it down on day one.
To put into numerical terms: take a 50-by-150-foot residential parcel, 7,500 square feet, the standard Austin SF-3 lot, with a 36-inch live oak ten feet inside the back fence.
The CRZ is a 36-foot radius around the trunk. Roughly 4,000 square feet of that circle lands inside the property line. The standard setbacks (25 feet rear, 5 feet side, 25 feet front) take about 2,500 square feet.
The tree takes more.
The tree doesn't have to be yours
Here is the part most people get wrong. The code doesn't care which side of the property line the trunk is on. It cares about the roots, and roots cross property lines.
Austin regulations (ECM § 3.3.2.A.1) require any tree outside the limits of construction whose CRZ extends onto the development site to be surveyed and protected as if it were on-site.
The math gets uncomfortable fast. A neighbor's 36-inch oak with a trunk standing 5 feet inside the neighbor's lot projects 31 feet of protected ground onto the subject property.
The owner of the subject property has no claim on the tree, no right to prune past their property line beyond a narrow common-law privilege, and no recourse if the neighbor refuses to cooperate. The city still requires the design to protect it.
That is exactly what was happening at 1711 Waterston. Twelve trees ringing the lot, ten of them on adjacent properties, all of their CRZs reaching in.
Board Member Darryl Pruett pushed back: "I have a real hard time thinking about trees on someone else's lot as a hardship on your lot." Board Member William Hodge was sharper still: "Buying a property and having great intentions but not following the rules does not constitute a hardship".
The board approved the variances anyway. The geometry didn't leave room for a defensible no.
What "preserved" actually means
The preservation criteria are the part civil engineers learn the hard way. A tree that survives demolition can still fail preservation.
A tree the city marks as preserved on the approved plan can be reclassified as removed if the contractor encroaches on the Quarter CRZ during construction, or pours an unpermitted patio inside the Half CRZ a year later. The reclassification triggers the standard 300 percent mitigation.
The owner is now on the hook for replacement trees on a tree still standing in the back yard.
That is why the survey isn't an afterthought. The tree survey decides where the foundation goes and where the driveway goes, before the architect picks up a pencil.
A licensed arborist runs $3,000 to $8,000 for a residential survey. On a lot with a meaningful tree, that money buys the document that informs the rest of the design.
Removing one is a process
Two pathways exist depending on stem size, and they are not interchangeable. A heritage tree where every stem is under 30 inches goes through an administrative variance, decided by the City Arborist and the Director of Development Services (LDC § 25-8-642).
A heritage tree with any stem at 30 inches or larger goes to the Land Use Commission, which means a public hearing, an Environmental Commission recommendation, and a vote (LDC § 25-8-643). The 30-inch line is the threshold between staff approval and public process.
The Land Use Commission pathway is harder because the standard is harder. The applicant has to show the tree is not viable, or that keeping it would prevent a reasonable use of the property, or that the design has been changed in every reasonable way to avoid removal.
Current Austin Development Services Director Keith Mars, then a City Arborist testifying on a West Campus student housing case at 2111 Rio Grande Street in May 2019, put the staff posture this way: "We try to be judicious with this type of condition. We will say when a tree needs to be preserved, and this is not that case."
Two heritage pecans stood where developer Jason Rogers wanted student housing: a 37-inch and a 34-inch. The Planning Commission voted 10-1 to allow removal of the smaller pecan and to require a 10-foot northward shift in the building to preserve the larger one.
Commissioner Karen McGraw dissented: "It seems like what we are really doing is horse-trading...I hate to see that happen, because heritage trees can't be replaced".
The replacement obligation is mechanical. Remove a 36-inch heritage tree, owe 108 caliper inches of replacement plantings, roughly 27 four-inch saplings, or the fee-in-lieu equivalent of $21,600 at the standard $200 per caliper inch (ECM § 3.5.4.A.1; Austin Code of Ordinances § 6-3-75).
The 300 percent rate is the floor. Commissions can and do impose higher rates as a condition of approval.
The process moves in stages, and the Environmental Commission is one voice in it. At the corner of Neches Street and Eighth Street downtown on October 27, 2015, developer Barton Creek Capital, represented by Dave Anderson of the Drenner Group, asked the Environmental Commission to allow removal of two live oaks (a 32-inch and a 30.5-inch) on a parking lot where they wanted to build a downtown hotel.
The commission voted 7-3 to recommend denial. Vice Chair Marisa Perales wrote the motion: "the applicant has not shown that removal of the tree is not based on the condition caused by the method chosen by the applicant to develop the property". A 150 percent mitigation offer didn't move that vote. Three weeks later, the Planning Commission voted 9-1 to approve the variance, clearing removal of one tree outright and allowing removal of the second if relocation proved unworkable.
Two commissions, the same record, different recommendations. The Environmental Commission applies the denial standard the ordinance lays out. The Planning Commission weighs that recommendation against the project as a whole.
The applicant prevailed at the second body. The first body's recommendation still set the conditions everything downstream had to clear.
Why this matters for an Austin lot
The 91 percent number is the one most people don't know. City Arborist Naomi Rotramel told the Environmental Commission in November 2024 that the city preserved 4,250 of 4,670 regulated survey inches in FY 2025 to date, a 91 percent preservation rate.
That number has also held across four decades of city politics, through several Council compositions and across reform movements that touched almost every other piece of Austin's land-use code. Austin's first tree ordinance dates to 1983, championed by Council Member Margret Hofmann, who is still memorialized in a grove of oaks near City Hall.
The Heritage Tree Ordinance that gave the rules their current form passed unanimously on February 4, 2010. When the Texas Senate attempted to preempt local tree ordinances during a 2017 special legislative session, Austin's rule survived a hundred-speaker hearing. When the city's 2023 HOME initiative reopened residential zoning to allow up to three units on lots that had been restricted to one, the same Council that liberalized density left the heritage tree rules untouched.
The key takeaway: few land-use rules in this city have moved through so many political eras intact.
The setback you can't see on the plat
In Austin, the mature canopy operates closer to public infrastructure than to private landscaping. The rules read that way once you see the geometry.
The argument over heritage trees in this city isn't really an argument about plants. It's an argument about whether a 200-year-old live oak belongs to the lot it grew up on or to the neighborhood that grew up around it. Austin has been answering that question the same way for forty years, through every other shift in city politics.
What that means for anyone looking at an Austin lot for the first time is that the survey that matters most isn't the boundary survey. It's the tree survey, run wide enough to capture every heritage and protected tree on the lot, and every heritage and protected tree on the lots next door whose roots reach in.
The plat tells you where the property line falls. The circles in the soil tell you where the project really starts.