Forest health is an important driver of overall watershed health and is a focus area in the Colorado Water Plan. A recent “Forest Health Study: 10 Takeaways to Inform the Colorado Water Plan” was completed by the Colorado Water Conservation Board (CWCB) to evaluate relevant forest health research, identify active workgroups focused on watershed and forest health, and assess modeling and analysis tools for critical decision making. The study was based off interviews with 30 subject matter experts on forest and watershed health and it identifies ten major takeaways that emerged from the research and interviews conducted in the study.
This effort will inform statewide dialogue around challenges and opportunities in forest health. This document can guide stakeholders in their local forest health and/or watershed health enhancement efforts and will be used to inform the Colorado Water Plan update.
The megafire era gripping the West isn’t just a threat to human development. Fires now burn so intensely that they literally reshape forests, shift tree species, and turn calm waterways into devastating mudflows.
A 2017 University of Colorado study analyzing 15 burn scars left from fires in Colorado and New Mexico found that as many as 80% of the plots did not contain new seedlings. In a 2020 follow-up study project under different climate change scenarios, the most severe scenario, where climate change continues unabated through 2050, showed as many as 95% of ponderosa pine and Douglas fir forests would not recover after a fire. In a “moderate” scenario where emissions decline after 2040, more than 80% of the forest would be replaced by scrubby grassland.
That, said study author Kyle Rodman, could have serious implications for waterways, due to the lack of established trees to stabilize soil and reduce the risk of flooding.
“Just because there aren’t trees doesn’t mean there’s no vegetation. Grasses and shrubs can hold back the soil, but it won’t be the same,” says Rodman, now a postdoctoral research assistant at the University of Wisconsin.
Nearly two decades later, the site of the 138,000-acre Hayman Fire, which burned in an area southwest of Denver in 2002, is still marred with patches of bare ground. That fire, according to a U.S. Forest Service (USFS) study, was so severe in areas that it consumed the canopy foliage as well as the seed bank for the forest’s ponderosa pines and Douglas firs, limiting regeneration. Overall, the study predicted “gradual return to preferred conditions” in the Hayman Fire area, though some of the worst-hit patches may see permanent vegetation changes.
In lower elevations, some of the heartier species, like the ponderosa pine and Douglas fir, are having trouble regrowing because of the increased heat and months-long drought. A 2018 study found that even seedlings of those species that were given supplemental water in burned areas had lower survival rates than expected because of the harsh natural conditions.
“When you’re planting a garden, those first few days are so critical. The plants need water to establish their roots and get healthy,” Rodman says. “Trees work a much longer timescale. Those first few years should be cool and wet and we just don’t have those conditions too often.”
Some tree species, like the high-elevation lodgepole pine, generally rely on fire because the heat helps them open and release seeds. But recent fires are burning so intensely that even lodgepole cones are consumed.
A 2020 study in BioScience found that burned forests are showing “major vegetation shifts” and recovering more slowly than expected. In some cases, heartier species might give way to drier shrub-dominated vegetation that can burn more easily. The study found that, generally, those post-fire “forested areas will have climate and fire regimes more suited to drier forest types and non-forest vegetation.”
That means that hearty forests used to adapting to natural changes are now facing conditions “outside the realm of the disturbances that some forests can handle,” says lead author Jonathan Coop, a professor of environment and sustainability at Western Colorado University.
“We have this paradigm that fire is a natural part of the forest and that forests will always recover,” Coop adds. “These days, we shouldn’t count on that.”
That vegetation shift is especially worrisome for waterways. Normally, forest floors soak in rain and snowmelt, releasing it to waterways slowly throughout the spring and summer. Burn-scarred watersheds, however, have faster runoff and a lower water yield because of the loss of natural material and because of hydrocarbons from smoke permeating the soil. A USFS analysis found that more than 50% of wildfire-scarred land area in Colorado showed increased erosion potential, mudslide threats, and sediment in streams for at least 3-5 years after a fire.
Those effects can last even longer depending on natural conditions, says USFS research engineer Pete Robichaud. The wild seasonal swings from climate change are challenging forests by dumping more precipitation on less stable ground.
“The drought cycle is bigger and the wet cycle is more intense,” Robichaud says. “The perfect storm is a high-severity fire followed by a high-intensity rainfall event.”
The harsh natural conditions, as well as widespread damage from bark beetles, has complicated typical recovery efforts. Some scientists say the rapid changes in forest conditions and fire characteristics make it hard to know what the best recovery strategy is. In some forests, for example, aspen trees that regenerate from low-ground structures rather than relying on seeds to sprout may dominate. Especially in low-elevation areas, shrubbier species like the Gambel oak may regrow faster in forests once driven by conifers.
While replanting is a natural step in recovery (USFS hosts six national nurseries that act as seed banks, although it has restrictions on where certain species can be planted), there are even concerns that the natural conditions should prompt a re-examination of how best to revitalize forests. Ultimately, Coop says, we should expect that forests may not look the same as they did in a pre-megafire era.
“I think this points to the need for all stakeholders and the public to start to think outside the box as far as how we evaluate the forests and ecosystems we depend on,” says Coop. “We might have to think about what ecosystems we are saving and under what circumstances we’ll have to let things go and let some changes unfold.”
When Denver’s early settlers built the High Line Canal back in the 1880s, little did they know what the future would hold for the 71-mile man-made waterway that stretches from Waterton Canyon southwest of Littleton all the way to Aurora.
The High Line Canal was originally designed to deliver irrigation water to farmers on the dry plains of Denver. While Denver Water still owns and uses the canal to deliver irrigation water to customers, the canal corridor also has grown into a recreational asset and an ecological resource for the metro area.
On the recreational side, each year around 500,000 people walk, run and ride the canal’s 71-mile maintenance road that also serves as a popular trail. As an ecological resource, some sections of the canal structure itself are now being used for stormwater management.
The evolution of the public’s use of the canal for recreation and stormwater management, along with its original role as a water delivery method, is one of the reasons why Denver Water and regional partners, including cities, counties, park and flood districts and stormwater management entities, have partnered with the High Line Canal Conservancy. The nonprofit organization’s mission is to preserve, protect and enhance the 71-mile canal in partnership with the public.
Denver Water plays an active role in the ongoing discussions about the canal’s future as it continues to serve its High Line customers. Because the canal has a junior water right and experiences high seepage and evaporation losses over large distances, Denver Water is looking for more reliable and efficient ways to deliver water to some of the High Line customers.
“As the canal’s role in the metro area evolves, Denver Water is committed to making sure it remains a beneficial asset to the community,” said Jeannine Shaw, government relations manager at Denver Water. “That’s why in 2020, the Denver Water Board of Commissioners approved a historic $10 million pledge to the High Line Canal Conservancy to invest in the long-term care and maintenance of the canal corridor.”
Included in the pledge is a piece of property and an office building located adjacent to the canal in Centennial for the Conservancy to use as its new headquarters.
As part of this evolution, the Conservancy, Denver Water and canal stakeholders are creating a new management structure called the Canal Collaborative to formally connect the regional partners as they guide the future of the canal.
“The collaborative helps us do more together than any one entity can do alone,” said Suzanna Fry Jones, senior director of programs and partnerships for the High Line Canal Conservancy. “The collaborative management structure will ensure this treasured resource is preserved, protected and enhanced as a regional legacy for future generations.”
The formalized structure will benefit citizens and the environment along all 71 miles of the canal as it winds its way through Denver as well as Adams, Arapahoe and Douglas counties.
The Canal Collaborative includes the High Line Canal Conservancy, Denver Water, Arapahoe and Douglas counties, the cities of Aurora, Denver, Cherry Hills Village, Greenwood Village and Littleton, the Highlands Ranch Metro District, the Mile High Flood District, the Southeast Metro Stormwater Authority and South Suburban Parks and Recreation.
“The collaborative is important because we need to have a group that brings together all of the jurisdictions so we can hear from each one of those entities and their communities about what’s most important to them,” said Nancy Sharpe, Arapahoe County Commissioner for District 2, which includes Centennial, Greenwood Village, a portion of Aurora and unincorporated central Arapahoe County.
The Conservancy was formed in 2014 and has developed “The Plan for the High Line Canal,” which lays out guidance for repurposing the corridor along with over 100 recommendations for new projects.
Here’s a look at some of the developments along the canal in recent years.
Under the new Stormwater Transformation and Enhancement Program, High Line Canal partners are looking at ways to allow and move stormwater through areas of the canal to improve water quality and manage local flooding in the South Platte River Basin. This is in addition to the canal’s existing irrigation delivery purposes.
Stormwater is any rain and snow that eventually flows off any impervious surface and into the canal.
Several structures have been built in or on the side of the canal to help manage the flow of stormwater through the channel.
The new structures that are located on the side of the canal help improve drainage on city streets and collect debris and trash before water enters the canal.
The structures being built inside the canal also help catch and stop debris and trash from flowing down the channel. They also temporarily slow down and detain water to filter out sediment.
These structures are designed to improve water quality before the water reaches receiving streams. Moving stormwater through the canal could provide an additional 100 days that the canal could be wet in some parts of the channel, which would benefit vegetation along the corridor while also enhancing the recreational user experience.
“Often times across the country, old utility and railroad corridors become degraded once their primary uses have been reduced, so we’re happy to see areas of the High Line Canal being maximized and transformed into green infrastructure,” Shaw said.
Along with Littleton and Denver, stormwater projects are also being implemented in Centennial, Douglas County and Greenwood Village with additional projects in progress. Learn more about the Stormwater Transformation and Enhancement Program in this video.
Denver Water and its regional partners also are exploring other opportunities to allow the canal structure to be used. In areas where it has adequate stormwater capacity the canal could provide additional benefits to the neighboring communities and their surrounding environment to improve water quality in the South Platte River basin.
“As we navigate the evolving future for the lands the High Line Canal irrigates, Denver Water is excited to further the work with our regional partners to find additional utility for this cherished resource,” Shaw said.
Tree canopy health
There are more than 23,000 mature trees along the High Line Canal, but many are at the end of their life span. The Conservancy is working with Denver Water and regional partners to remove dead trees and trim others to improve overall tree health and safety along the canal’s recreational trail.
To maintain the canal’s urban forest, the Conservancy’s Plan recommends planting 3,500 new trees by 2030. The species of trees being planted will be more drought tolerant than many of the old cottonwood trees currently along the canal.
A major goal of the Conservancy and the Canal Collaborative is to make it easier, safer and more fun to walk or ride on the canal’s recreational trail. The Conservancy is working with local jurisdictions to add new pedestrian bridges, trailheads, underpasses, mile markers and wayfinding signs.
Canal Improvement Zones
Under The Plan, the Conservancy has worked with the community and jurisdictional partners to identify nine Canal Improvement Zones. These are locations where residents asked for trail enhancements to increase physical activity, foster community connections and create access points to nature.
Many of the sites are in diverse neighborhoods where the canal corridor has been historically under-utilized and lacked investment.
Enhancements may include pedestrian bridges, improved trail access, benches, signs, gathering spots and play areas.
The first location to see new projects is the Laredo Highline neighborhood in Aurora, thanks to a $180,000 grant from the Colorado Health Foundation and an additional $180,000 from Arapahoe County.
“I grew up in the Laredo Highline neighborhood and the canal has always helped bring the community together,” said Aurora resident Janak Garg. “We’re really looking forward to the new bridge and other improvements coming to the neighborhood.”
New mile markers
A very noticeable and welcome improvement to the trail is the addition of new mile markers. In the past, there were a variety of mile markers with different mileage from each jurisdiction, which made it confusing for hikers and bikers.
Now there are new Colorado red sandstone mile markers that line the trail from start to finish, paid for through donations by the Conservancy’s founding partners.
Most of the markers have a quote or message from the founding partners, like Al Galperin who lives near the South Quebec Way Trailhead, whose message reads: “Be the reason someone smiles today.”
“I hope it brings a little bit of extra joy to people on the trail,” Galperin said. “It’s nice to be able to help out and see all the new features coming to the canal.”
“It’s inspiring to see all these improvements and we’re excited for the future of the canal,” Shaw said. “The Conservancy and all of the partners are doing a great job leading the way and working with Denver Water and the community.”
Visit highlinecanal.org to sign up for monthly emails for information on events throughout the year. The website also provides information about history of the canal, new projects and volunteer opportunities.