Tree Care + Planting

Together we are revitalizing the High Line Canal’s tree canopy

Tree Canopy Care

Now 140 years old, the High Line Canal is outliving its historic function as an irrigation utility and has taken on new life as a recreational, ecological, and stormwater management resource. With increased trail use, an aging tree population, and scarce water supplies in the West, comprehensive care of one of the Canal’s most beloved assets–the tree canopy–is a top priority. The Conservancy, along with its partners Denver Water and the adjacent jurisdictions, are collaboratively taking action to maintain and revitalize the tree canopy. In 2018, these partners initiated a tree maintenance program which prioritizes safety for recreational users and the long-term health of the tree canopy. This significant, 71-mile-long project is only possible with the commitment of the Conservancy and partners’ joint funding, staff and expertise.

Learn More About Tree Canopy Care

Tree Planting Program

New tree plantings are a key component of the Conservancy’s effort to protect and revitalize the Canal’s canopy. The Conservancy launched its tree planting program in the fall of 2021, planting 175 trees along the corridor with the support of volunteers—representing the largest tree planting effort on the High Line since 1990! The Conservancy is continuing to work closely with local jurisdictions to develop planting plans that ensure the best approach is being taken along each reach of the Canal, planting the right type of tree with the best irrigation strategy in the appropriate location.

Learn More About our Tree Planting Program

Resources

Learn more about the Canal’s plant community and the work the Conservancy and our partners are doing to understand the corridor’s natural resources and enhance the ecological health of the greenway.

Tree Canopy Care

Tree Canopy Care

Tree care and maintenance is taking place along the entire 71-mile Canal corridor, from Douglas County to Aurora. With over 23,000 mature trees along the corridor, continuous care and maintenance is required to steward the Canal’s canopy and ensure a safe and vibrant trail corridor. Since 2018, over 1,000 unhealthy trees have been pruned or removed from the corridor. Tree maintenance crews continue to work along the Canal, prioritizing trees that pose a safety concern.

The tree canopy care program aims to:

  • Maintain a safe environment for trail users and adjacent property owners.
  • Preserve and enhance the health of the tree canopy.
  • Support a healthy ecosystem for plants and wildlife.

Changing Conditions

Cottonwoods are the most abundant trees on the Canal, composing 40% of the corridor’s canopy. Historically, these riparian trees were able to establish and thrive on the corridor due to the abundance of irrigation water that allowed the man-made Canal to mimic a natural waterway. Many of these cottonwoods are now reaching the end of their lifespans—lifespans which have seen conditions along the Canal change as the corridor grew from an irrigation utility into a stormwater management system and regional recreation trail. As the varied landscapes of the Canal evolve with changing times and limited water, the Conservancy continues to work closely with Denver Water and the jurisdictions to:

  • Maintain data on the trees and their condition as a tool for long-term management.
  • Leverage private funding to ensure long-term, high-quality care of the entire tree canopy.
  • Develop tree planting programs to revitalize the canopy for years to come.

Tree Canopy Care FAQs

For all tree-related questions and non-emergency concerns, contact the High Line Canal Conservancy. For us to best assist you, please email hello@highlinecanal.org and include:

  • Details about the location of the tree (nearest address or lat/long)
  • Photos of the tree in question

If there is an immediate public safety risk, please call Denver Water at (303) 893-2444 during regular business hours, Monday-Friday, 7:30 am-5:30 pm. For afterhours emergencies, call (303) 628-6801.

If a property owner is concerned about a tree potentially causing damage to their property, it is the property owner’s responsibility to first accurately determine the property boundaries and whose tree the property is on. Property owners are advised that fence lines are not always an accurate indicator of the property line. Colorado law allows a property owner to cut overhanging limbs at their property line. The property owner is responsible for removing any debris resulting from pruning the tree.

Arborists performing work on along the Canal have documented the location and type of work needed for the trees utilizing GIS mapping applications. Trees scheduled for maintenance have a painted mark to help field crews locate specific trees. Tree maintenance work includes full removals, habitat prunes (where portions of trunks are left standing to provide habitat for wildlife), and safety prunes.

Arborists working along the Canal do their best to minimize disruptions along the trail while pruning or, in some cases, removing trees. However, in certain areas, there may be trail closures for short periods of time. Stay up to date on potential trail interruptions by checking the Trail Updates page or follow the Conservancy on Facebook and Twitter.

Russian olive is an invasive species which displaces native vegetation and depletes scarce water resources along the Canal corridor. The Conservancy began the first large-scale Russian olive removal project in 2022 in partnership with Mile High Youth Corp, clearing Russian olive along the Canal in Denver, unincorporated Arapahoe County, Centennial, and Greenwood Village. This pilot project will inform future Russian Olive mitigation efforts. Learn more about Russian olive and our work with the Mile High Youth Corps.

Depending on the location and the condition of the wood, there are several things that could happen. It could remain in place on the corridor as wildlife habitat, it could be mulched and brought to a mulch-yard for use or resale, or it could be brought to a composting facility. Considerations will also be made to repurpose tree wood for trail signage, nature play areas, benches, and other enhancements along the Canal.

The tree canopy care project is possible because of joint funding from Denver Water and the jurisdictional partners, as well as private citizens through the Conservancy. The Conservancy is committed to working with its partners to ensure continued tree care maintenance is a priority in order to protect a healthy ecosystem and beautiful natural setting along the Canal. Learn how to get involved and support the Conservancy’s work to steward the Canal’s natural resources.

Tree Planting Project

Tree Planting Project Overview

The 71 miles of the High Line Canal are home to over 23,000 mature trees (trees larger than six inches in diameter), making the Canal a vital component of the region’s urban forest. Cottonwoods have been the defining tree of the Canal corridor for over a century, with a 2016 inventory finding cottonwoods to compose over 40% of the Canal’s canopy. As many of these cottonwoods near the end of their lifespan and become increasingly stressed by low water availability, it is crucial that new trees are planted along the corridor to revitalize the canopy for years to come. To this end, The Plan recommends planting 3,500 trees, or 50 trees per mile on average, along the Canal corridor over 15 years. So far, with our partners we have:

  • Planted 325 new trees across the Canal in Centennial, Denver, Greenwood Village, and Littleton.
  • Collaborated on the creation of a tree planting palette that prioritizes drought-tolerant species which will help the corridor’s canopy become more resilient.
  • Initiated the development of planting plans that ensure the best approach is being taken along each reach of the Canal, evaluating both the potential to water new plantings by truck and the possibility of extending irrigation lines along the corridor in some areas.

Tree Planting Palette

As Denver Water reduces its reliance on the Canal for irrigation delivery and local jurisdictions embrace its potential as green stormwater infrastructure, the tree canopy must evolve to reflect these changing conditions. The Conservancy’s tree planting palette prioritizes drought-tolerant species that will provide shade as the Canal loses parts of its cottonwood canopy. The Conservancy is also piloting the planting of a small number of native, riparian trees in reaches of the Canal that hold stormwater and in locations where trees can be planted near the base of the Canal channel. This blend of drought-tolerant and native trees will create a resilient canopy for the benefit of the environment and trail users alike.

  • Xeric Species
    ‘Xeric’ refers to species that are drought-tolerant and able to survive in dry environments

    • Bur Oak
    • Catalapa
    • Chinkapin Oak
    • Common Hackberry
    • Honeylocust
    • Kentucky Coffeetree
    • Shumard Oak
  • Native, Riparian Species
    ‘Riparian’ refers to species that naturally occur along waterways and are adapted to wet environments

    • Boxelder
    • Narrowleaf Cottonwood
    • Plains Cottonwood

Tree Planting Program FAQs

The Plan for the High Line Canal recommends planting 3,500 trees between 2021 and 2035, an addition of 50 trees per mile on average. In 2021, a total of 225 trees were planted across the corridor: Greenwood Village planted 50 trees and the Conservancy raised funds to plant 175 trees with the help of volunteers. In 2022 and 2023, Greenwood Village planted a total of 100 new trees along the corridor. Additional tree planting projects are being planned for 2024 and beyond.

In 2021, the Conservancy planted 75 trees in Denver and unincorporated Arapahoe County, 50 trees in Centennial, and 50 trees in Littleton. As the Conservancy raises funds for tree planting, project locations will be dictated by need, availability of stormwater to support native tree establishment, and funding opportunities. The Conservancy’s goal is to work closely with local jurisdictions to develop planting plans that ensure the best approach is being taken along each reach of the Canal, planting the right type of tree with the right irrigation strategy in the right location.

New plantings consist mostly of xeric species that have low water requirements. These hardy species will increase the diversity and resiliency of the Canal’s canopy as many of the corridor’s cottonwoods reach the end of their lifespan and struggle with reduced water availability. The Conservancy is also piloting the planting a small number of native, riparian trees in certain areas of the Canal that have higher water availability. Scroll back up to see the tree planting palette.

The Conservancy has raised funds to water the newly planted trees for three years and will evaluate additional watering needs at that time. Due to the lack of irrigation infrastructure along most reaches of the Canal, watering will typically be done by truck. Conservancy staff and volunteers will monitor the health of the saplings and conduct seasonal maintenance, such as weeding and application of trunk wrap. Learn more about volunteering opportunities.

You may see green bags around saplings after they are planted. These are tree watering bags. The bags can be filled with water, which is slowly released to deeply water the root zone of the newly planted trees and provide a consistent level of moisture in the soil.

This tree planting initiative is made possible through support from individuals, foundations, and jurisdictional partners. The Denver tree plantings were funded by Great Outdoors Colorado (GOCO), while Centennial and Greenwood Village purchased trees for their jurisdictions. Your support has also made this program possible! The Conservancy has utilized individual donations from Colorado Gives Day to support this tree planting program.

Community input is more important than ever as the Conservancy focuses on implementing critical project across all 71 miles. Get involved!

Speak Up for the Canal

Together, we are making strides towards preserving, protecting and enhancing the Canal. Learn more!

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