NASA and US Forest Service collaborate to record the age of America’s oldest trees.

A century-old sugar maple in Wisconsin. Five hundred year old cedar in Oklahoma. Oak trees fifty feet wide in Georgia. These trees adorn our nation’s old-growth forests, and scientists say they hold unexplored mysteries from their roots to their rings.

In an effort to nurture these resources, on Earth Day 2022, the Biden administration called on the Department of Agriculture and the Bureau of Land Management to identify and map these forests on federal lands. A year later, that work yielded the first-ever national inventory of mature and old-growth forests—widely described as forests in an advanced stage of development. And with some help from NASA, the public will soon be able to view some of these forests like never before.

The nation’s old-growth forests include different types of trees in different regions, from towering redwoods and 5,000-year-old pines to diminutive coniferous junipers whose age and grandeur are less immediately apparent. For decades, the US Forest Service has studied such trees on hundreds of thousands of plots across the country, but the agency has yet to issue any official accounting. To identify and define these forests, the team analyzed decades of field-collected data from a wide range of forest types and ecoregions, gathering public input in the process.

America’s forests help absorb more than 10% of our annual greenhouse gas emissions. While younger plants accumulate carbon more quickly, old-growth forests generally contain more biomass and store more carbon. Not only are these ecosystems essential to the country’s clean air and water, they are particularly important to tribal nations, they support local economies, and they maintain biodiversity.

Complementing the Forest Service’s research on Earth, some NASA-funded scientists are using a space-based instrument called GEDI (Global Ecosystem Dynamics Investigation) to provide a detailed picture of these forests. From its perch on the International Space Station, GEDI’s laser imager (liDAR) instrument is able to peer through dense canopies to observe nearly all of Earth’s temperate and tropical forests. By recording the way laser pulses are reflected off the ground and plant material (stems, twigs, leaves) at different heights, GEDI makes detailed measurements of the three-dimensional structure of the planet’s forests and fields. It can even estimate the weight, height, and vertical structure of trees.

“Partnering with NASA will help us do analyzes that we haven’t been able to do in the past,” said Jamie Barbour, who leads the US Forest Service’s Old Growth Initiative. “From space, we will be able to search and learn about more places.”

Old trees, constant threats

Researchers report that large portions of old-growth forests in the United States have been lost in recent centuries. Logging greatly altered the forests that Europeans found when they came to North America, while invasive insects and diseases have recently destroyed important tree species. The surviving forests also face a new generation of threats, including wildfires fueled by climate change, extreme precipitation events, chronic temperature and drought stress.

Species such as American beech, eastern hemlock, American elm and ash have largely dwindled, said Neil Pederson, an ecologist and tree ring specialist (tree punctuation specialist) at Harvard University. Preserving what remains is critical, he said, if we’re going to continue to make fundamental discoveries about trees, such as how long they live and why, and what they can tell us about Earth’s past.

“This project challenges us to really step back and think about why these ancient forests are so important to us and how we can be more proactive in addressing the problems they face,” said Marine Palmer, Forest Service Technical Team Leader.

“We sometimes imagine these forests were never touched by humans, but we have to look further back in history and understand that Aboriginal people have been intentionally managing their forests for thousands of years. And when we think about the threat posed by climate change, it becomes a larger conversation about the need to be Active stewards of our landscapes and ecosystems.”

Tree rings are a data record of Earth’s climate, Pederson said, and they teach us things we don’t usually learn about in textbooks. “In the United States, our best meteorological records are only about 130 years old,” he said. “Living and fossil trees allow us to reconstruct the history of temperature and precipitation over hundreds or thousands of years, which helps us better understand dry and rainy periods.”

The Forest Service will continue to work alongside partners like NASA to collect aerial and satellite imagery and map ancient and ancient growth at finer scales. Such data could also help the USFS establish a long-term surveillance system. Meanwhile, an interagency team of experts will analyze and assess the threats and risks to these areas.

GEDI collected four years of forest observations around the world, before it recently went into hibernation on the International Space Station. An extension of the GEDI mission is currently under discussion, and if the extension is approved, monitoring of mature and old-growth forests is expected to resume when they return to service in two years.

said Ralph Dupaier, a professor at the University of Maryland and principal investigator for the GEDI mission. “This radically changes how we move forward with these types of endeavors.”