Carmel Urban Forestry publishes an approved species list (last revised 3/28/2024) whose "Undesirable Trees" section reads like a field guide to what fills older Hamilton County streets: silver maple (shallow roots, weak wood), Callery pear, pin oak, red maple and all Fraxinus for emerald ash borer. Approved large street trees run to swamp white oak, bur oak, chinkapin oak, hackberry, male-only ginkgo, thornless honeylocust, Kentucky coffeetree, baldcypress and London planetree; note Callery pear is discouraged locally but is not yet banned in Indiana — 312 IAC 18-3-25 currently lists 44 species without it. That context matters for northern catalpa: catalpa is the coarse old tree on the back fence line — heart-shaped leaves the size of a hand, orchid-like white flowers in june, and foot-and-a-half seed pods. Removing a northern catalpa around Carmel runs roughly $400–$1,900, and in Village of WestClay, Brookshire and Woodland Springs access is usually what decides where in that range you land.
What's actually growing in Carmel
Carmel Urban Forestry publishes an approved species list (last revised 3/28/2024) whose "Undesirable Trees" section reads like a field guide to what fills older Hamilton County streets: silver maple (shallow roots, weak wood), Callery pear, pin oak, red maple and all Fraxinus for emerald ash borer. Approved large street trees run to swamp white oak, bur oak, chinkapin oak, hackberry, male-only ginkgo, thornless honeylocust, Kentucky coffeetree, baldcypress and London planetree; note Callery pear is discouraged locally but is not yet banned in Indiana — 312 IAC 18-3-25 currently lists 44 species without it.
Carmel's housing stock, and what it means for tree size
Carmel went from 1,442 residents in 1960 to 18,272 by 1980, 37,733 by 2000 and 99,757 by 2020, so the bulk of the housing is 1970s through 2000s — I-465 construction beginning in 1967 set it off, and the town incorporated as a city in 1976. Old Town Carmel and Home Place, an early-20th-century interurban-era settlement annexed by Carmel in 2018, carry 60-to-100-year canopy, while the 1990s and 2000s subdivisions are on a first generation of nursery trees now 25 to 35 years old and just reaching conflict size.
What's specific to northern catalpa
The one to know is verticillium wilt, which catalpa is highly susceptible to — sudden wilting on one limb or one side of the crown, early defoliation, and brown streaking in the sapwood under the bark of the affected branch. Stress is being stripped bare by catalpa sphinx caterpillars in August and refoliating or simply leafing out fine next spring; dying is one-sided limb death repeating across consecutive years with vascular streaking, and since there is no cure and no effective fungicide, the replant has to be a non-susceptible species.
Hamilton County rules
Carmel's code section 6-64 is titled "Planting and Removal of Trees and Shrub Regulations" and sits in the streets-and-sidewalks division of Chapter 6, alongside 6-55 covering trees and shrubs that obstruct streets and sidewalks — so the city's active regulation is aimed at the public way, plus landscape and buffer plantings approved through development plan review by Urban Forestry. I could not verify the exact text of 6-64 or confirm whether any permit applies to removing a tree standing entirely in a private back yard; contact Carmel Urban Forestry through the city's Department of Community Services before assuming, and check HOA covenants, which in most Carmel subdivisions are stricter than the city.