Rollinger Tree Project partners

The Rollinger Tree Collection 50-Year Survey Project is a collaboration between Denver Botanic Gardens, Denver’s Office of the City Forester, Colorado State University (CSU) Extension, Colorado State Forest Service, the Colorado Tree Coalition and other local participants to revisit a survey of major trees done in 1968 by Alan Rollinger in order to gain insight into the history, health and future of Denver’s urban trees.


In 1968, Al Rollinger was a young landscape designer, recently graduated from CSU. Curious about the kinds of trees growing in Denver, he decided to do a survey of the more unusual trees, ones other than the very commonly planted species like American elm, silver maple, honeylocust and green ash. Therefore, he undertook the huge effort of doing a street-by-street survey, noting the species, location, diameter and height of over 1,100 trees of 46 species. In 1969, Rollinger documented the results of his survey in a written report.

The Project

Now, almost 50 years later, we realize how valuable the data collected in this survey is to analyze the health, mortality and growth patterns of various species in the Denver area.

We are in the process of finding, measuring and taking photographs of the trees surveyed in 1968 to see which are still alive and to determine growth patterns. The data will be analyzed and stored in a Denver Office of the City Forester database and will be reported in a book publication with before and after pictures, stories about some of the most interesting or unique trees and implications for the future of trees in Denver. We expect this study will provide a wealth of information that can be used to assess which tree species are best suited to Denver’s climate and act as a guide to future tree planting.

Project Status

The Rollinger Tree Project exceeded most of the 2017 goals. The team surveyed over 900 trees (well over 3/4 of the total) and determined that roughly 2/3 of them are still alive. The survey sessions that took place over the years provided many unexpected benefits:

  • We learned an enormous amount about trees and those who care for them.
  • We realize more than ever how much everyone values our urban tree canopy.
  • Since many of the trees are on private property, it’s given us a chance to talk to homeowners about these special trees and sometimes learn their interesting stories and histories.
  • We’re beginning to see patterns about how well trees have fared in public parks versus neighborhoods, or in some neighborhoods versus others.
  • Staff from Denver Botanic Gardens, Denver City Forestry, Colorado State Forestry, local arborists and master gardeners enjoyed the relationship-building collaboration.
  • More than anything, this project is revealing that our valuable old trees are very much at risk as the city grows and changes; we’ve seen how many trees have disappeared in areas with the greatest change and redevelopment since 1968.

In 2018, we look forward to finishing data collection, analyzing the data and sharing the information in presentations, publications and on the web in the coming years.

Submit Consent Form Online

If we have notified you that one of the Rollinger Trees is located on your property and you would like to fill out the consent form online, click on the orange button at the top of this page.

Please contact Ann Frazier at for more information.