Front Range Planting by the Numbers

What we plant vs what survives here

Here is the gap nobody puts side by side. We pulled the public, city-managed tree inventories for Denver, Aurora, Boulder, and Longmont (street right-of-way plus park and other public-property trees) - the metro plains, the foothills, and the northern corridor - counted what is actually in the ground, and checked each species against the 2024 Front Range Tree Recommendation List. A large share of what got planted is exactly what the current list says to stop planting.

Ash is the clearest case. About 15 percent of the trees in Colorado's urban forests are ash, the species emerald ash borer kills. [Colorado State Forest Service] Emerald ash borer is now established here, so each of those is a future removal. Our own count of Denver's public trees puts green and white ash at 11.1% of the total, and the city agrees: Denver's own 2024 Urban Forest Strategic Plan reports that of the city's 117,496 public trees, ash and maple each make up over 10 percent of the canopy (about 14 percent ash, 12 percent maple). [City and County of Denver] The canopy leans on a short list either way: the five most-planted species are 27.2% of every public tree Denver tracks.

Denver: 319,190 public trees, 404 species

In Denver, the single most-planted species is Ash, Green at 7.8% and the biggest genus is Acer at 14.4%. By the 10-20-30 diversity guideline [PlanIT Geo] (no species over 10%, no genus over 20%), the canopy as a whole is more balanced than its reputation. The problem is narrower and sharper: ash alone is 11.1% of the trees, and 22.5% of everything planted is species the list now rates Not Recommended.

Aurora: 60,939 public trees, 250 species

In Aurora, the single most-planted species is Honeylocust at 16.3% and the biggest genus is Gleditsia at 16.3%. By the 10-20-30 diversity guideline [PlanIT Geo] (no species over 10%, no genus over 20%), the canopy as a whole is more balanced than its reputation. The problem is narrower and sharper: ash alone is 9.5% of the trees, and 17.8% of everything planted is species the list now rates Not Recommended.

Boulder: 49,924 public trees, 436 species

In Boulder, the single most-planted species is Honeylocust at 7.2% and the biggest genus is Acer at 12.5%. By the 10-20-30 diversity guideline [PlanIT Geo] (no species over 10%, no genus over 20%), the canopy as a whole is more balanced than its reputation. The problem is narrower and sharper: ash alone is 7.2% of the trees, and 14.7% of everything planted is species the list now rates Not Recommended.

Longmont: 22,061 public trees, 281 species

In Longmont, the single most-planted species is Honeylocust Species at 6.7% and the biggest genus is Pinus at 11.6%. By the 10-20-30 diversity guideline [PlanIT Geo] (no species over 10%, no genus over 20%), the canopy as a whole is more balanced than its reputation. The problem is narrower and sharper: ash alone is 8.2% of the trees, and 11.3% of everything planted is species the list now rates Not Recommended.

The cities we cannot join directly tell the same story. Fort Collins does not publish a joinable species inventory, but its 2025 Urban Forest Strategic Plan reports green ash at about 12 percent and honeylocust about 11 percent of its roughly 60,000 public trees - both above the recommended 10 percent single-species limit - with emerald ash borer threatening the 13 percent of public trees that are ash. [City of Fort Collins]

The Front Range is not an outlier. A study of more than 5 million trees across 63 US cities found maples and oaks dominate urban canopies nationwide and green ash is among the most common species, with a median effective diversity of just 26 species per city (native share ranged widely, median 45.6 percent). [McCoy et al.] Green ash being one of the most-planted city trees in the country, right as emerald ash borer spreads, is a national problem we share acutely. The fix is the same everywhere: plant a wider mix.

Underused trees to plant instead

None of this means a bare parkway. These are catalog trees rated Recommended or Recommended for Most Sites that barely show up in the inventories, one per genus, leaning native and pollinator-friendly. The diversification is the whole point.

• Hawthorn Crataegus douglasii Colorado native, high pollinator value
• Juniper Juniperus scopulorum Colorado native
• Douglas-fir Pseudotsuga menziesii var. glauca Colorado native
• Fir Abies concolor Colorado native
• Chinese lantern tree Koelreuteria paniculata high pollinator value
• Yellowwood Cladrastis kentukea high pollinator value
• Ornamental types Prunus nigra 'Princess Kay' high pollinator value
• Dogwood Cornus mas high pollinator value

The catalog by the numbers

Step back from any one yard and look at the whole rated palette: 480 plants (228 trees, 82 shrubs, 109 perennials, 61 groundcovers). The composition says a lot about what actually works here.

On the 2024 tree list specifically, of 228 trees rated, 16 are Not Recommended outright, and the rest spread across Recommended, Recommended for Most Sites, and Conditionally Recommended. Low-water dominance is not a preference, it is what survives our clay, alkalinity, and dry winters.

The toughest trees for a Colorado yard

We scored every recommended tree 0 to 10 for raw toughness: hail, wind, and salt tolerance, drought hardiness, and how long it lives. One per genus, so the list is varied, not five junipers. These are the trees that shrug off a Front Range summer.

And the most demanding

The other end of the same scale: thirsty, brittle, or short-lived enough that they ask for more than they give back here.

Every city has a tree that loves it there

A handful of natives top almost every Front Range city: Juniper, One-Seed (8 cities), Juniper, Rocky Mountain (8 cities), Oak, Gambel (4 cities), Cypress, Arizona Cypress (3 cities), Pine, Bristlecone(foxtail) (2 cities). They are the dependable backbone. More interesting is each city's most distinctively suited tree, the one that fits its particular mix of hail, wind, cold, fire risk, and deer better than it fits anywhere else.

Distinctiveness is the gap between a tree's hazard-fit score for that city and its average score across all nine, so it surfaces the local specialist rather than the universal all-star.

How the Front Range compares

Pull back to the whole country. In the largest study of US city trees [McCoy et al.], Denver and Aurora plant strikingly few state-native trees - 13.5% and 8.6% - far below the 63-city median of about 46%. (Some wetter cities plant even fewer; the meaningful comparison is to cities with our climate.)

The honest test is against cities with the same constraint. Other dry Western cities work from a similarly thin native-tree palette, yet Albuquerque (25.5%) and Las Vegas (26.7%) plant roughly two to three times the native share Denver and Aurora do - and Colorado Springs, leaning on native ponderosa pine, reaches 30.3%. So part of the Front Range gap is real constraint (Colorado has few native shade trees that thrive in town), but not all of it - it is also a planting habit.

One thread ties it together: green ash is the single most-planted tree in Denver, and in Minneapolis and Milwaukee too. The Front Range shares its ash reliance with the cold-Midwest cities now losing those trees to emerald ash borer. Denver's overall diversity is fine (about 49 effective species); the exposure is specific - too much ash, too few natives.

What it costs, and what your city pays back

A Kentucky bluegrass lawn needs roughly 18 to 20 gallons of water per square foot per year, while native grasses use about 6, according to Denver Water figures cited by 5280. [5280] Denver Water's water-use benchmark for a typical mixed-use landscape is about 12 gallons per square foot per year. [Denver Water] That gap is why nearly every Front Range water provider now pays you to pull out thirsty turf. Ranked by the most comparable number, dollars per square foot of lawn removed (5 of the nine cities publish one):

Amounts are quoted verbatim from each provider and were verified against their conservation pages; some are flat caps, some are per-square-foot, and toilet or nozzle rebates are excluded.

However you garden, the numbers have a list

• Dog owners. 17.7% of the catalog (85 plants) is toxic to dogs, which means the other 82.3% is not. See the plants toxic to dogs list to know which is which.
• Pollinator gardeners. 55.2% (265 plants) rate high for pollinator value, concentrated in the perennials and shrubs.
• Native-plant advocates. 29.0% (139) are Colorado or regional natives. See native trees to start.

Methodology and sources

Two kinds of numbers here, kept separate on purpose. The internal figures (the catalog composition, the toughness scores, the per-city distinctiveness) are computed straight from our published 480-plant dataset and the committed inventory snapshots, so anyone can re-derive them. The external figures are third-party data we cannot recompute, and each is cited inline where it appears.

The catalog is rated against the 2024 Front Range Tree Recommendation List, CSU Extension, and Plant Select. Inventory species are matched to the catalog by botanical name, falling back to the genus where the list rates a whole genus (this is how all ash resolves to Not Recommended). Records identified only to genus (an inventory label like "maple species") join only at that ash-or-pear genus level, so they are not counted as Not Recommended even if some are; the Not-Recommended shares are therefore a conservative floor, not a ceiling. The data is public. Check our math.

Two honest caveats. The municipal inventories are open data and carry a little record-level noise. Denver and Boulder include empty planting sites and stumps, which we drop (Longmont publishes standing trees only); and across all three there is the occasional blank or mismatched common name. We aggregate by botanical name and show the most common label, so a stray mislabel cannot mis-rank a species; any residual sits well under a tenth of a percent. And where we put our own ash count (11 percent of about 319,000 public trees) next to the city's (14 percent of 117,496), the two use different inventories, dates, and totals; we cite both because they agree on the point that matters, that ash sits above the 10 percent line.

What we plant: municipal inventories

• Denver: 319,190 living trees across 404 species, from City and County of Denver Tree Inventory (Parks & Recreation) (accessed 2026-06-22).
• Boulder: 49,924 living trees across 436 species, from City of Boulder Tree Inventory (Open Data) (accessed 2026-06-22).
• Aurora: 60,939 living trees across 250 species, from City of Aurora Public Tree Inventory (Open Data) (accessed 2026-06-22).
• Longmont: 22,061 living trees across 281 species, from City of Longmont Public Tree Inventory (Forestry) (accessed 2026-06-22). This inventory records species as common names; we resolved 99.8% of trees to botanical names using a crosswalk built from the Denver and Boulder data (the rest are left unclassified).

Cited external figures

• About 15 percent of the trees in Colorado's urban forests are ash, the species emerald ash borer kills. Colorado State Forest Service, 2025 Report on the Health of Colorado's Forests (Emerald Ash Borer) (accessed 2026-06-22).
• Denver's own 2024 Urban Forest Strategic Plan reports that of the city's 117,496 public trees, ash and maple each make up over 10 percent of the canopy (about 14 percent ash, 12 percent maple). City and County of Denver, Urban Forest Strategic Plan (2024) (accessed 2026-06-22).
• A study of more than 5 million trees across 63 US cities found maples and oaks dominate urban canopies nationwide and green ash is among the most common species, with a median effective diversity of just 26 species per city (native share ranged widely, median 45.6 percent). McCoy et al., "Species clustering, climate effects, and introduced species in 5 million city trees across 63 US cities" (eLife, 2022) (accessed 2026-06-22).
• The widely used 10-20-30 rule for urban forest diversity: no more than 10 percent of a tree population from one species, 20 percent from one genus, or 30 percent from one family. PlanIT Geo, "The 10-20-30 Rule for Tree Diversity" (accessed 2026-06-22).
• A Kentucky bluegrass lawn needs roughly 18 to 20 gallons of water per square foot per year, while native grasses use about 6, according to Denver Water figures cited by 5280. 5280, "A Beginner's Guide to Xeriscape in Denver" (citing Denver Water) (accessed 2026-06-22).
• Denver Water's water-use benchmark for a typical mixed-use landscape is about 12 gallons per square foot per year. Denver Water, "How much water does your landscape really need?" (accessed 2026-06-22).
• Fort Collins does not publish a joinable species inventory, but its 2025 Urban Forest Strategic Plan reports green ash at about 12 percent and honeylocust about 11 percent of its roughly 60,000 public trees - both above the recommended 10 percent single-species limit - with emerald ash borer threatening the 13 percent of public trees that are ash. City of Fort Collins, Urban Forest Strategic Plan (2025) (accessed 2026-06-22).