Sugar Pine Trees are Dying Faster than they are Regenerating

Replanting program continues apace

Those who spend time in the Sierra Nevada or the Pacific Coast ranges of California and Oregon know sugar pine trees for dropping cones that grow to be two feet long, the largest pine cones in the world. The iconic western tree can grow to be 200 feet tall and live for 500 years, but a study published in 2020 in the journal Ecosphere showed that over the 20-year study period, sugar pine and western white pine trees are dying off faster than they are regenerating.  

The study looked at four species of white pine in Sequoia and Kings Canyon national parks. Research showed that whitebark and foxtail pines are marginally increasing in numbers. The analysis also found that unsustainable sugar pine mortality was largely a result of the invasive fungal pathogen, white pine blister rust. 

According to the study, blister rust is more common in lower, warmer elevation bands where sugar pine and western white pine grow. Whitebark and foxtail trees flourish at higher, cooler elevations and are thereby less exposed to blister rust.

Maria Mircheva is executive director of the Sugar Pine Foundation.

“The founder of the Sugar Pine Foundation (John Pickett) was actually working on a project at the (U.S.) Forest Service restoring sugar pine,” Mircheva said by phone. “He was tasked with trying to identify healthy sugar pines for blister rust resistance testing. And he thought, ‘Wow, this is a worthwhile project. There needs to be more effort put into this.’” 

So Pickett filed the 501(c)(3) paperwork and formed the Sugar Pine Foundation in 2004. Mircheva became executive director in 2007 and said the Forest Service has many responsibilities to include forest health but doesn’t always have the resources needed to manage problems in detail from historical building maintenance to environmental restoration. Nonprofits like the Sugar Pine Foundation work to fill in the gaps.

“Sugar pines are part of our Sierra mixed conifer forest. They used to be about 20 to 25 percent (of the forest), but they’re less than five percent now, between one and six percent due to the pressure of initial logging and also the nonnative fungus white pine blister rust, and drought, beetles. There are a lot of pressures,” Mircheva said.  

Sugar pine trees in the forest near Lake Tahoe – photo: DL Bliss

It’s important to save the sugar pine because biodiversity makes the forest more resilient to trauma. 

“When the forest has different species such as sugar pine, Jeffrey pine, white fir, incense cedar, ten different species have different adaptations,” Mircheva explained. “Biodiversity is important because when one stressor comes through the forest, for example fire or the Jeffrey pine beetle, then it would effect some species more than others.

“The Jeffery pines and the sugar pines are fire adapted. They have thick bark. They self prune at lower branches, and they don’t burn as much in fire as white fir, lodgepole, and some of the other species.”

Some trees may be drought adapted, but a lack of water poses a threat to all plant life. Without water, trees die. 

“Jeffrey pine seems better adapted to drought conditions than sugar pine or incense cedar, so they (sugar pine, incense cedar) tend to die in bigger numbers when there are consecutive years of drought,” Mircheva said.

In addition to changes in the form and timing of precipitation, a warming climate brings many challenges for trees, in particular, insects.

“Mountain pine beetles, I participated in a survey a number of years ago, and now they’re having two flights, so they’re having babies twice, instead of once because the summers are longer and it’s warmer longer,” said Mircheva. “And in the winter it doesn’t freeze enough to pare some of their offspring, so they exist in bigger numbers.”

A sugar pine cone – photo: the Sugar Pine Foundation

The most distinct threat to sugar pines comes from the nonnative fungus, white pine blister rust.

“White pine blister rust affects white pines, which is five-needle pines, five needles in a bunch, but it also affects some species of bushes and flowers like Indian Paintbrush and currants.

“The reason why the flowers and the bushes are not so affected as the pines is because they shed their leaves every year, so then they shed the fungus,” Mircheva said. “Pines only shed their needles every three years or so, so the infection gets into the needles and into the branch and into the trunk of the tree and girdles it, and the tree dies.”

The Foundation is searching for trees with a natural, genetic resistance to the fungus to reproduce and replant. They’ve found that roughly 2 percent of all white pines are fungus resistant.

“For years we’ve been going and collecting pinecones with a giant sling shot. We need at least three pine cones from a tree in order to grow seedlings, which are then infected with the fungus and see if they survive. So it’s a very simple testing method that’s been used for years and done at the Forest Service nursery in Placerville.”

Volunteers use a slingshot to harvest sugar pine cones to identify trees with a natural genetic resistance to the invasive fungus, white pine blister rust – photo: the Sugar Pine Foundation

Once the fungus-resistant trees or “seed trees” have been identified, they return to the trees and collect more seeds. The seeds are planted and raised at both the U.S. Forest Service nursery in Placerville and the California Department of Forestry facility in Etna.

“We climb them to get the cones every fall, and from these seeds we grow one-year-old seedlings, and then we plant them in restoration projects such as fire scars, forest thinning projects, erosion control projects.” 

With the help of some 500 volunteers, Mircheva said the Foundation has expanded into tree watering.

“Every Tuesday we have a volunteer event in South Lake Tahoe. We go and water our trees, especially during drought, especially this summer. We have found that our survival rates increase from 20 percent to 80 percent when trees are watered at least once per month.

“We can’t water all our trees because we plant 10,000 (a year), but we do what we can.” 

Hugh Denno climbs a sugar pine to harvest seeds – photo: Martin Rubio

New DNA analysis methods can shorten the time needed to identify fungus-resistant trees.

“Another project we’re doing this summer is trying to collect, especially in Truckee because our numbers of resistant trees are lower in Truckee, we’re trying to collect needles from some healthy sugar pines in order to test them by genetic test for the fungus-resistant gene.”

Since 2005, the Foundation has tested over 500 sugar pines and has identified 66 fungus-resistant seed trees in the Tahoe–Truckee region. The nonprofit has planted nearly 150,000 trees over time, restored nearly 3,000 acres, and engaged some 11,000 volunteers in the effort. But the forest is large, and the challenges for sugar pines are numerous. Is Mircheva optimistic?

“I am definitely optimistic. I actually studied environmental science and management at U.C. Santa Barbara, and it’s a very depressing major,” Mircheva chuckled. “All you learn in environmental science is gloom and doom, and I have to say, restoration is one of the more positive fields where you feel that you’re making a difference because you’re trying to make things better and to stop people from making things worse, so it is definitely something positive and hopeful.

“Being practical, can we bring the sugar pine numbers to what they historically were? I think that would be very difficult. The Sugar Pine Foundation cannot do it. But we’re hoping to have some key populations of sugar pine survive. So basically there would be pockets where sugar pines still exist and they won’t just disappear.”

Top photo credit and caption: Sugar pine cones laden with sap near Lake Tahoe – photo: Hugh Denno


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