Downtown Denver’s Tree Canopy: From 4% to a Perfect 10
The odds are against Denver’s trees. Denver is in the Western High Plains, a semi-arid grassland, with low moisture, high elevation, and wide temperature extremes. The arid conditions bring only 8 to 15 inches of precipitation annually. Very few trees grow here naturally. Because of these conditions, Denver’s trees require attention and care above and beyond those located in other US cities.
Downtown Denver’s trees face another strike against them. Here, the conventional tree pit design is a 5×5 ft. which does not provide the tree with enough soil volume for root growth. Additionally, the current design constricts trunk growth and allows for salt runoff and trash build up in the tree pit. A tree pit of this size provides 75 cubic feet of soil. Even the City standard design of a 5×15 ft. tree pit only provides 225 cubic feet of soil. It is well documented that at least 1,000 cubic feet of soil are needed for the tree to reach maturity. Because of our current infrastructure, trees in Downtown Denver have an average lifespan of about 12 years. When measured against 20 other US cities’ downtowns, our center city ranked the lowest for urban tree canopy with 4%. With the number of people living, working and playing in Downtown Denver, the need to provide a healthy prosperous tree canopy is more essential than ever.
To get to a perfect 10%
To take Denver’s urban forest to the next level, we must rethink the infrastructure surrounding trees. We have to go above and beyond what is required. Existing tree pits should be expanded from 5×5 ft. pits to, at least, 5×15 ft. pits. Several streets in Downtown Denver lack trees altogether. In areas where circumstances allow, new tree pits should be installed through the Urban Forest Initiative. To ensure the appropriate amount of soil volume, suspended pavement system technology (silva cells or strata cells) should be incorporated. Suspended pavement systems use soil volumes to support large tree growth, provide on-site stormwater management, and support the weight of the sidewalk.
The Downtown Denver Partnership will install or expand 500 tree pits in the next 36 months and expand the urban tree canopy to 10%. To achieve this goal, the Partnership will work with the City and County of Denver, philanthropists, and property owners to enhance tree infrastructure in the public realm. Community education and awareness of the importance of our urban forest is also a vital step to getting to 10%. Join us for a Tree Data Collection Event on February 12.