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Cottonwood, catalpa, silver maple, blue spruce and white oak are the fastest-growing tree varietals for Colorado’s Front Range communities, while hawthorn, piñon pine and hackberry are some of the slowest growers, according to a report by the Colorado State Forest Service.

White ash varietals, including the highly popular autumn purple common to Front Range neighborhoods, also are fast-growing but are no longer recommended for Colorado because of the threat of being killed by the non-native pest emerald ash borer.

The report characterized the long-term growth of 19 common urban tree species grown on publicly maintained land in Westminster over 24 years, as tracked by the forest service and City of Westminster. However, tree growth rates should not be the only factor to consider when buying trees at a local nursery.

“Factors like insect and disease susceptibility, hardiness in our harsh climate and soils, and shorter lifespan in some faster-growing species should also be considered when selecting the right tree,” said Keith Wood, community forestry program manager and lead author of the study.

He warns that some fast-growing shade trees, including cottonwoods and silver maples, are prone to branch breakage in the state’s late spring and early fall snows, while slower growers like hackberry and honeylocust thrive in this area.

Another consideration when selecting trees should be diversity within a community, to make the urban forest more resilient to future insect and disease threats, Wood said.

The Front Range Tree Recommendation List, offered by the Colorado Tree Coalition, includes descriptions of trees suitable for the area and drawbacks to consider. The list, along with an ash tree replacement selection tool and species diversity calculator, is available at www.coloradotrees.org.  

The full growth-rate study results are available at http://csfs.colostate.edu/csfs/media/sites/22/2017/08/FINAL-Growth-Rate-Study-2016-02Aug2017.pdf.