A more-than-decadelong effort to thin Front Range forests to reduce fire danger has brought more bees, more flowers and increased resilience to climate change, new research shows.
The raw number and the diversity of bees and plants exploded a few years after ponderosa pine forests were restored to a “pre-European” state, researchers from Colorado State and Utah State universities found.
“We found that if you cut trees and open up the canopy, between three and 10 years later, you see a pretty good response,” said Seth Davis, associate professor of forest and rangeland stewardship at Colorado State University and co-author of a study recently published in “Ecological Applications.”
“Forest restoration and forest thinning is one of the ways that we can conserve our native communities.”
For thousands of years, natural fires have been an integral part of healthy forest ecosystems in the West. Small fires that clear out underbrush every five to 30 years as well as more devastating fires that can raze the forest to the ground every 50 to 100 or more years clear the way for new growth. Native Americans were known to set small fires to clear out undergrowth for better hunting and regeneration of valuable plants, but did not cause major changes in the ecosystem. Then, beginning in 1859, Euro-Americans flooded into Colorado seeking gold and silver.
“Suddenly, in a span of decades, the Colorado Rockies were engulfed by this new, highly unpredictable world of commodity capitalism, of smelters and railroad investment, of boomtowns and sudden busts, of landscape changes so fundamental that they dwarfed the modest human impacts made over the prior 10 centuries,” historical geographer William Wyckoff wrote in his book “Creating Colorado.”
Vast swaths of the Front Range forests were cleared to obtain wood for mining, construction and railroads. Extensive fires also surged across the landscape, fueled by accidental and intentional fires.
To combat the rampant and unregulated logging of these forests, the federal government in the early years of the 20th century created the White River, Pike, and Arapaho and Roosevelt national forests along the Front Range and high into the Rockies. At about the same time, firefighters began trying to suppress all fires.
As a result, over the past century, dense forests with thick undergrowth have grown up across the Front Range and the entire West. Many of the plants that thrived in the pre-European forests disappeared from the now shady forest floor. And with them went many of the animals that ate and pollinated them.
“You end up with a rather homogenous landscape that doesn’t have a lot of flowers in it,” Davis said. “You end up with a situation where you can’t have a lot of native bees there.”
In Colorado and across the nation, sharply declining populations of native bumblebees and nonnative honeybees have raised concerns about these important pollinators at the base of the food web. Loss and fragmentation of bee-friendly habitat, pesticides, diseases and climate change have all been blamed. Colorado recently limited access to a particularly harmful class of pesticide, neonicotinoids, and commissioned a study to evaluate the state of pollinators across the state, presumably with an eye toward more conservation. Colorado Parks and Wildlife, however, has no authority to manage or protect insects like bees, beetles and other pollinators.
Dense forests that have grown up over the past century have fostered more frequent devastating crown fires that are extremely difficult to fight and have destroyed thousands of homes. Ponderosa pine forests, growing between 6,000 and 9,000 feet in elevation, are especially prone to burning.
In 2020 alone, five devastating fires burned 25% of the Arapaho and Roosevelt national forests. Drier and warmer weather from climate change are further increasing the fire danger.
In an attempt to reduce fire danger and restore forests across the West closer to their healthier, pre-European state, the federal government in 2009 funded a 10-year program, called the Collaborative Forest Landscape Restoration Program. Thirty-two thousand acres — or 50 square miles — of the most vulnerable and degraded forests along the Front Range were chosen for restoration, through physical removal of excess trees and undergrowth and low-intensity prescribed fires.
It is still too early to know if the thinning has reduced fire danger. However, thinning did have a beneficial effect on at least one large fire.
☀️ READ MORE
“The Cameron Peak fire burned into some of the areas that did have that thinning and prescribed fire,” said Tony Cheng, director of the Colorado Forest Restoration Institute at Colorado State University. “That fire basically kind of laid down once it hit those thinned areas. It transitioned from being a running crown fire into being more of a grass kind of surface fire, which is exactly the kind of fire that we would have expected more of historically. So that was really kind of an eyewitness demonstration where a lot of that work really did have an impact on the fire.”
Flowers were three times more abundant in thinned forest plots
Davis and his colleagues studied 15 thinned and 15 unthinned plots near Estes Park, Lyons and Buffalo Creek. The thinned plots were sunnier, warmer and more open.
“Think ‘open and park-like’, or ‘savannah woodland,’” Davis wrote in an email. In contrast, the unthinned forest was colder and darker with pine needles and woody material covering the forest floor. “Think ‘thick pine forest that wants to burn up,’” he wrote.
Sweat bees, so named because of their attraction to human sweat, were the most common group of bees. Bumblebees were the second-most common group and two of the most common species. Leafcutter bees were another group often found in the forests.
Compiling a list of the plants and bees provides a very limited picture of the forest ecosystem. It is kind of like naming the characters in a play without performing the play. It does not tell you how the characters interact, who is important and who plays a minor role.
To get a more direct and relevant measure of the ecological effects of forest thinning, Davis and his colleagues cataloged which bees visited which plants.
They found an impressively richer, more dense and resilient web of life. While the bee population roughly doubled, the number of interactions between bees and plants rose eightfold and there were five times as many unique connections between specific bee species and plant species.
The researchers illustrated the interactions in a diagram, which visually depicts a richer, more complex web of life.
“Yeah, it’s kind of mind-blowing,” Davis said. “You just see there’s just far more diversity or more complexity.
“You get the idea that if you lost one or two of the flowers or one or two of the bees out of this system, the whole network doesn’t just collapse and fall apart. Whereas on these control plots, if you remove one or two things, you just got a lot more vulnerable ecosystem.”
“This paper is a strong piece of evidence for the ecosystem benefits of forest thinning in areas where fire has been suppressed and the canopy is overgrown,” said Amy Yarger, director of horticulture at the Butterfly Pavilion. She was not involved in the research. “With climate change and biodiversity loss posing existential threats, mindful forest management is key for conservation and for preserving our way of life in Colorado.”
By mapping those interactions, Davis was able to identify several plant species that are particularly important for a healthy ponderosa pine forest: blue mist penstemon (Penstemon virens); field chickweed or prairie mouse-ear (Cerastium arvense); sand dune or Western wallflower (Erysimum capitatum); and pineywoods geranium (Geranium caespitosum).
In addition to being visited by many bees, these plants also connect different groups of bees and plants that interact, sort of like the person in high school who was both a jock and part of the theater crowd. These connector plants help make the network more resilient should one or more species of plant or bee disappear.
“Here are some really key species for supporting a lot of biodiversity of pollinators, which in turn supports biodiversity of plants,” said Julian Resasco, assistant professor of ecology and evolutionary biology at the University of Colorado. “Things that maintain the integrity and the diversity of these ecosystems make them more robust to other threats, like climate change.”
The researchers recommended that forest managers seed ponderosa pine forests with these plants to promote a robust pollinator network. They also could be good plants for people to plant in their gardens. “These are good choices for planting because they’re going to support the bee-flower interaction network,” Davis said.
He believes the environmental benefits extend beyond bees and plants. “We’re sort of measuring one little component of the overall food web here,” Davis said. “By bolstering their abundances, you’re also bolstering the abundances of things which prey upon them, like predators, which could be birds and other animals.” Another study from 2020 suggests that the thinned forests also benefited bird populations.
The thinning by the original landscape restoration program ended in 2019. Since then, the federal Infrastructure Investment and Jobs Act and Inflation Reduction Act have funneled more money into the program and the Forest Service has announced a strategy to reduce wildfire hazards across the West. The initial funding for that program, however, will run out in three to four years, said the Forest Restoration Institute’s Cheng, and it is not clear what will happen after that.
“I think the question is always what comes next to sustain the funding for this continued forest management,” Cheng said.