Casper, WY Invasive Plant Rules: Prohibited Species (2026)

Casper Municipal Code § 12.32.160 lists four categories of trees and shrubs that cannot be planted, or caused to be planted, on any public place in the city. Subsection A bars cotton-bearing cottonwood trees except within forty feet of the North Platte River bank, where the cotton nuisance matters less for nearby sidewalks and storm drains. Subsection B bans female box elder trees (Acer negundo) outright, with no river exception. Subsection C bars willows reaching ten feet or more in height (genus salix), again except within forty feet of the river bank.

Subsection D folds in state law by prohibiting any tree or shrub species the state of Wyoming has designated a noxious weed under Wyoming Statutes Section 11-5-102, naming Russian olive and tamarisk as examples the city code calls out directly. Section 12.32.020.E separately defines a "noxious tree" for the chapter as one designated under the Wyoming Weed and Pest Control Act, Wyoming Statutes Section 11-5-101 et seq., tying the local list to the state's own updates. Because these species compete aggressively with cottonwoods and willows along the North Platte River corridor and can clog irrigation and drainage infrastructure, the city restricts them from parkways, medians and other public grounds citywide rather than just along the river.

A violation, such as planting a banned species on a city parkway or park, is a misdemeanor under the chapter-wide penalty in Section 12.32.190, punishable by a fine of up to seven hundred fifty dollars under Chapter 1.28.