If you had to guess how many big trees in Denver would survive over a 50-year period, what would you say? And have you ever wondered which types of trees have fared the best over time in the Denver area? Thanks to Al Rollinger and a team consisting of Denver Botanic Gardens, Denver City foresters, and many other arborists and tree enthusiasts, we now know the answers.
Back in the late 1960s, Al Rollinger was a young landscape designer, wondering why there seemed to be so few tree species growing in Denver. When someone challenged him on this belief, he took the dare and declared he would find out. So, he spent the next two years walking through the parks and driving up and down the streets of Denver and even some of the outlying suburbs, cataloguing and measuring all the large, more interesting and less common tree species he found. Overall, he had a list of 1,148 trees in 45 different species.
Panayoti Kelaidis came across this tree report many years ago in the library and realized its potential value. When the 50-year anniversary of the report approached, he thought it would be interesting to see how many of these trees are still alive and how much they’ve grown. So once again, we took that dare. Only this time, we had an army of 75 arborists and tree enthusiasts, and modern technologies such as GPS, laser range finders and iPads. And it still took us more than two years.
From 2016 to 2018, we digitized the original paper report, mapped it and then drove all over Denver to look for and measure trees. The ones in public areas like parks and schools were easy. It got a little trickier when they were in people’s yards. Can you picture someone knocking on your door and asking to measure your tree? But by talking to all these people, we learned how much people value their trees, and how our trees intertwine with the history of our city.
And the answer to the question of how many trees survived over the 50 years? Sixty percent. To find out which tree species have done the best over this time period, and other findings of the project, please download the project report.
Some of the trees that had the highest survival rate were the Kentucky coffee tree, oaks (in particular the bur oak), Golden rain tree, Northern red oak and English oak.
You can read more about the study in this article in Westword.