Thinning Colorado forests to reduce fire danger also helps bees and flowers

Attempts to reduce front range forests over a decade in the making to reduce fire danger have produced more bees, more flowers and increased resilience to climate change, according to new research.

Researchers from the Universities of Colorado and Utah found that the number and diversity of bees and plants increased dramatically a few years after the ponderosa pine forests were restored to their "pre-European" state. This is reported by coloradosun.com.

"We found that if you cut the trees and open the crown after thirty years, you will see a pretty good response. Restoring and thinning forests is one way to preserve our native communities," said Seth Davis, associate professor of forest and rangeland management at Colorado State University and co-author of a study recently published in Ecological Applications.

For thousands of years, wildfires have been an integral part of healthy forest ecosystems in the West. Small fires that destroy brush every 5 to 30 years, as well as more destructive fires that can level a forest every 50 to 100 years or more, clear the way for new growth. Native Americans are known to have set small fires to clear undergrowth for better hunting and regeneration of valuable plants, but this did not cause major changes in the ecosystem. Then, starting in 1859, Euro-Americans poured into Colorado in search of gold and silver.

Huge tracts of the Front Range forests were logged to produce timber for mines, construction, and railroads. Large fires also broke out across the landscape, caused by accidental and intentional fires.

To combat the unrestrained and unregulated logging of these forests, the federal government created the White River, Pike, Arapahoe, and Roosevelt National Forests along the Front Range and high in the Rocky Mountains in the early 20th century. Around the same time, firefighters began trying to extinguish all fires.

As a result, over the past century, dense forests with undergrowth have grown throughout the Front Range and the West. Many of the plants that grew in pre-European forests have disappeared from the current shady forest floor. And with them went many of the animals that ate and pollinated them.

"You get a pretty homogeneous landscape with not a lot of flowers. You end up in a situation where you can't have a lot of native bees," Davis said.

In Colorado and across the country, dramatic declines in the populations of native bumblebees and non-native honeybees have raised concerns about these important pollinators at the heart of the food web. The loss and fragmentation of bee-friendly habitat, pesticides, disease, and climate change are all being blamed. Colorado recently restricted access to a particularly harmful class of pesticides, neonicotinoids, and commissioned a study to assess the status of pollinators across the state, likely with a view to greater conservation. However, Colorado Parks and Wildlife does not have the authority to manage or protect insects such as bees, beetles, and other pollinators.

In an effort to reduce fire danger and restore forests in the West closer to their healthier, pre-European state, the federal government in 2009 funded a 10-year program called the Cooperative Forest Landscape Restoration Program. Thirty-two thousand acres - or 50 square miles - of the most vulnerable and degraded forests along the Front Range were selected for restoration through physical removal of excess trees and undergrowth and low-set fires.

The 2020 wildfire season was historic as it burned more acres than in any year before. But Colorado has a complicated past with its forests.

"The Cameron Peak fire burned some of the areas that really had that kind of sparse and established fire. That fire died out when it got into these thinned areas. It went from being an ongoing upland fire to a grass surface fire, which is exactly the type of fire that we've expected more of historically. So this was an eyewitness demonstration where a lot of this work really made a difference in the fire," said Tony Cheng, director of the Colorado Forest Restoration Institute at Colorado State University.

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.

Sweat bees, so named because they are attracted to human sweat, were the most common group of bees. Bumblebees were the second most common group and the two most common species. Another group often found in forests were leafcutters.

Making a list of plants and bees gives a very limited picture of the forest ecosystem. To get a more direct and relevant measure of the ecological impacts of forest thinning, Davis and his colleagues catalogued which bees visited which plants.

What they found was a strikingly richer, denser, and more resilient web of life. While the bee population roughly doubled, the number of interactions between bees and plants increased eightfold, and there were five times as many unique connections between certain bee species and plants.

"You realize that if you lose one or two flowers or one or two bees from this system, the whole network doesn't just collapse and disintegrate. Whereas in these control plots, if you remove one or two things, you're going to have a much more vulnerable ecosystem."

Davis was able to identify several plant species that are particularly important to a healthy ponderosa pine forest: blue mist penstemon (Penstemon virens); field or field mouseweed (Cerastium arvense); sand dune or western flower (Erysimum capitatum); and pine geranium (Geranium caespitosum).

The researchers recommended that forest managers seed ponderosa pine forests with these plants to promote a strong pollinator network. They can also be good plants for people to plant in their gardens. "They're a good choice to plant because they will support the bee-flower interaction network," Davis said.

He believes the environmental benefits extend beyond the bees and the plants. "We're kind of measuring one small component of the overall food web," Davis said. "As you increase their numbers, you also increase the number of things that prey on them, such as predators, which could be birds and other animals."

Thinning as part of the original landscape restoration program ended in 2019. Since then, the federal Infrastructure Investment and Jobs Act and the American Recovery and Reinvestment Act have directed more money to the program, and the Forest Service has announced a strategy to reduce wildfire danger in the West. However, the initial funding for this program will run out in three to four years, and it is unclear what will happen after that.