A world of pines, rooted in 100 years of research

Entrance to the Eddy Arboretum in Placerville, California. Forest Service photo.

Walk into the Eddy Arboretum in Placerville, California, and you can travel much of the world, pine by pine, without leaving the foothills of the Sierra Nevada. This exceptionally diverse arboretum, part of the Institute of Forest Genetics, is one of the best-documented collections of pine species grown together in a single place.

The collection captured the imagination of Kara Kaur Sanghera, an Oak Ridge Institute for Science and Education fellow at the Institute of Forest Genetics. What fascinated her most was the chance to encounter species from around the world, including Aleppo pine from Syria and Eldar pine from Iran, Iraq, and Turkey.

“This arboretum represents a unity among Earth’s ecosystems, before geopolitics made arbitrary boundaries that only one species, humans, adhere to,” she says. It holds about 70 percent of the world's pine species, including trees with very limited or declining native populations.

Sanghera wanted to help visitors recognize the arboretum’s different tree species and understand how their diversity supports ecosystem stability. Using computer mapping skills, she created the Eddy Arboretum Interactive Map.

“Cartographic storytelling is one of the best ways to promote public engagement for ecosystem-related projects,” she says. Now anyone with a phone or computer can use the interactive map to explore this little-known scientific resource.

A bold idea is planted

The arboretum began in 1925 with James G. Eddy, a lumberman who noticed that forests were being cut faster than they could regenerate. Eddy wondered whether the tools of plant breeding could help restore forests so that they could continue to provide high-quality lumber for the growing U.S. economy.

Eddy sought pine seeds from around the world for his collection, bringing them back to plant in the soil of California’s mild Mediterranean climate, hospitable to many pine species. Eventually the institute, including the arboretum, was transferred to the Forest Service and became part of the Pacific Southwest Research Station. Early work there helped establish forest genetics as a practical science. Today, research at the institute spans forest disease, bark beetle ecology, biodiversity conservation, fire resilience, and the genetics that help trees respond to a changing climate.

100 years of science for trees and forests

The arboretum's story is a fitting way to celebrate the centennial of the Pacific Southwest Research Station, which was established in 1926 at the University of California, Berkeley. A century later, it continues to deliver research, technology, and tools that support forest management in California, Hawai‘i, and the U.S.-affiliated Pacific Islands.

The questions have evolved, but the focus remains practical: How do forests respond to wildfire, drought, insects, and disease—and how can managers help them endure?

Long-term collections such as the Eddy Arboretum help provide answers. With many species growing under the same conditions, researchers can compare how genetics shape growth, survival, drought tolerance, and resistance to insects and disease.

That knowledge is increasingly valuable as managers replant landscapes after wildfire and prepare for warmer, drier conditions. Sanghera contributed to the Experimental Network for Assisted Migration and Establishment Silviculture (ENAMES), led by Forest Service scientists Jessica Wright, Christopher Looney, and Robert Slesak. ENAMES scientists and land managers are testing whether seed sources adapted to hotter, drier climates can improve reforestation success.

For Wright, the connection between ENAMES and the Eddy Arboretum lies in the long view each requires: “A technician at the institute once told me that trees are books and a collection of trees is a library. The Eddy Arboretum is that kind of library: trees planted generations ago are still teaching us today. With ENAMES, we are making the same investment in the future. When you plant a tree, you are planting knowledge for generations to come.”

Invisible stories come to light 

Despite its significance, the Eddy Arboretum has flown under the radar. Visitors might walk through admiring the shady canopy without realizing the depth of history and biodiversity around them or that many of the species are considered threatened, as determined by the International Union for Conservation of Nature.

Sanghera’s interactive map brings the arboretum’s hidden story into view. Starting with a 1937 map and decades of records, she pieced together its history block by block and tree by tree. Map users can select a block of trees to find common and scientific names, native ranges, planting years, and conservation status in the wild. 

“How can you expect people to care about species decline when they don’t know what the different species are?” Sanghera says. 

The map makes that first step—knowing what is there—easy and inviting. It also makes a century of scientific investment visible: trees planted to answer one generation’s questions are now helping scientists confront challenges that their planters could not have foreseen. 

That is the power of long-term research at the Pacific Southwest Research Station. Work begun by one generation becomes a living resource for the next. At the Eddy Arboretum, the past is still growing—and still helping shape the forests of the future.