Pando (tree)

Pando (from Latin pando 'I spread') is the world's largest tree, a quaking aspen (Populus tremuloides) located in Sevier County, Utah, United States, in the Fishlake National Forest. A male clonal organism, Pando has an estimated 47,000 stems (ramets) that appear to be individual trees but are not, because those stems are connected by a root system that spans 42.8 ha (106 acres). Pando is the largest tree by weight and landmass and the largest known aspen clone. Pando was identified as a single living organism because each of its stems possesses identical genetic markers. The massive interconnected root system coordinates energy production, defense and regeneration across the tree's landmass. Pando spans 1.08 km × 0.72 km (0.67 mi × 0.45 mi) at its widest expanse along of the southwestern edge of the Fishlake Basin and lies 0.69 km (0.43 mi) to the west of Fish Lake, the largest natural mountain freshwater lake in Utah. Pando's landmass spreads from 2,700 m (8,900 ft) above sea level to approximately 2,773 m (9,098 ft) above sea level along the western side of a steep basin wall. Pando is estimated to weigh collectively 6,000 tonnes (6,000,000 kg), or 13.2 million pounds, making it the heaviest known organism. The Pando Tree's 43-hectare (106-acre) expanse also makes Pando the largest tree of any kind, by way of landmass.
Systems of classification used to define large trees vary considerably, leading to some confusion about Pando's status. Within the United States, the Official Register of Champion Trees defines the largest trees in a species-specific way; in this case, Pando is the largest aspen tree (Populus tremuloides). In forestry, the largest trees are measured by the greatest volume of a single stem, regardless of species. In that case, the General Sherman Tree is the largest unitary (single-stem) tree. While many emphasize that Pando is the largest clonal organism, other large trees, including Redwoods can also reproduce via cloning. Pando being the heaviest tree and the largest tree by landmass, while also being the largest aspen clone leaves the Pando Tree in a class of its own.
Since the early 2000s, little information has been adequately corroborated about Pando's origins and how its genetic integrity has been sustained over a long period of time, conservatively between 9,000 and 16,000 years old-by the latest (2024) estimate. Researchers have argued that Pando's future is uncertain due to a combination of factors including drought, cattle grazing, and fire suppression. In terms of drought, Pando's long lived nature suggests it has survived droughts that have driven out human societies for centuries at a time. In terms of grazing, a majority of Pando's land mass is fenced for permanent protection and management as a unique tree. In terms of cattle grazing, it is only permitted on a volume basis for 10 days a year in October, weather permitting in a small edge of Pando's expanse. Additionally, in 2023, local grazers group 7-Mile Grazers signed off on a plan that would bring remaining portions of Pando into protective care under the "Pando Protection Plan", which would bring nearly 34 hectares (84 acres) of the tree into protective care. In terms of fire suppression, research indicates Pando has survived fires that would have likely leveled the tree many times, after which Pando regenerated itself from the root system. The same research also indicates large-scale fire events are infrequent, which may be owed to the fact that aspen are water-heavy trees and thus, naturally fire resistant, earning them the name "asbestos forests" among wildfire scientists. There is broad consensus that wildlife controls and protection from deer and elk who feed on the new growth faster than it can reach maturity are critical to Pando's future and care. Protection systems coupled with ongoing monitoring and restoration efforts have been shown to be the most effective, dating back to the first projects to protect and care for the tree in the late 1980s and early 1990s, with new projects under way.
Friends of Pando and the Fishlake National Forest partners to study and protect the Pando Tree working alongside Utah Division of Wildlife Resources. Notable organizations that also study and advocate to protect Pando's care include Western Aspen Alliance and Grand Canyon Trust.
The Pando tree was identified in 1976 by Jerry Kemperman and Burton V. Barnes. A posthumous biography by Barnes' colleague, Daniel Kashian, details Pando's discovery:
Work by Fishlake National Forest to understand and protect the tree began in 1987, according to interviews and articles written by Fishlake Forest as well as accounts gathered by Friends of Pando. Based on Barnes and Kempermans's 1976 paper noting Pando's discovery, Michael Grant, Jeffrey Mitton, and Yan Linhart of the University of Colorado at Boulder re-examined the clone in 1992 and described Pando as a single male aspen clone based on its morphological characteristics such as pollen production, leaves, and root structure. Michael Grant named the tree "Pando" which is Latin for "I spread" in an editorial which was later published in Discover Magazine. A large scale genetic sampling and analysis was published in 2008 by Jennifer DeWoody, Karen Mock, Valerie Hipkins and Carol Rowe. The research team's genetic study confirmed morphological analysis by Barnes and Kemperman as well as Mitton, Grant and Linhart thus, verifying Pando's size and scale of operation.
In late 1987, Fishlake National Forest began work to remove diseased trees and promote new growth using coppicing (a form of mechanical stimulation), which works by simultaneously removing diseased stems, while also stimulating the hormone response that spurs new growth. In 1993, Fishlake National Forest began work on the "Aspen Regeneration Project", installing fences to help control deer and elk who threatened to destroy the productive results of work to spur and protect new growth. Today, 53 acres of Pando is protected by 8-foot fences to control populations of mule deer (Odocoileus hemionus) and elk (Cervus canadensis), and to control human uses, such as permitted grazing by domestic cattle (Bos taurus). Additional fencing protections are to be added in 2025 bringing approximately 84 acres of Pando's landmass into protective care or around 80% of the tree's landmass.
Regeneration rates in portions of the "Aspen Regeneration Project" which started in the 1990s, showed promise based on photographic evidence and repeated survey plots by land managers, scientists and conservation groups between 1993 and today. Despite this, many have argued more work needs to be done to control wildlife, as the Pando Tree is surrounded by 700 square miles of de facto wildlife preserve managed by people, groups and agencies who do not have Pando's sustainability as a central concern in their land management policies. Paul Rogers and Darren McAvoy of Utah State University completed an assessment of Pando's status in 2018 and stressed the importance of reducing herbivory by mule deer and elk as critical to conserving Pando. In 2019, Rogers and Jan Šebesta surveyed other vegetation within Pando besides aspen, finding additional support for their 2018 conclusions and found that interactions between browsing and management strategy may have had adverse effects on Pando's long-term resilience to change. In 2023, a team of researchers, land managers, wildlife biologists and citizen scientists groups began long-term programs to monitor deer and elk using GPS collars and wildlife cameras to better understand wildlife, as well as deer and elk browsing on the tree. In 2022, Executive Order 14702 directed the US Forest Service to inventory old growth and mature forest as part of a plan to protect mature and old growth forest. Data submitted by Fishlake National Forest defined Pando's landmass as mature meaning it could be eligible for special care and protections.
Most agree, based on Barnes' work and later work, that Pando encompasses 42.89 hectares (106 acres), weighs an estimated 6,000 metric tons (6,600 short tons) or 13.2 million pounds, and features an estimated 47,000 stems, which die individually and are replaced by genetically identical stems that are sent up from the tree's vast root system, a process known as "suckering". The root system is estimated to be several thousand years old, with habitat modeling suggesting a maximum age of 14,000 years and 16,000 years by the latest (2024) estimate. Individual stems do not typically live more than 100–130 years.
Mitton and Grant summarize the development of stems in aspen clones:
Due to the progressive replacement of stems and roots, the overall age of an aspen clone cannot be determined from tree rings. Speculations on Pando's age have ranged between 80,000 years to 1 million years old. Many news sources list Pando's age as 80,000 years old, but this claim derives from a now-removed National Park Service web page, which redacted that claim in 2023 and, was inconsistent with the Forest Service's post ice-age estimate. Glaciers repeatedly formed on the Fish Lake Plateau over the past several hundred thousand years and the mountains above Pando's landmass were crowned by glaciers as recently as the last glacial maximum. Ages greater than approximately 16,000 years therefore require Pando to have survived climate conditions during the Pinedale glaciation, something that appears unlikely under current estimates of Pando's age and modeling of variations in local climate. A 2017 paper by Chen Ding et al. seems to support US Forest Service claims that Pando could not be older than the last Glacial Maximum in the area based on paleo-climate models and genetic traits of aspen sites throughout North America. A 2024 paper indicates the age could be between 16,000 and 80,000 years old again based on the first somatic mutation model of the tree, but, that research has not finished peer review and also relies on older material and testing methods. Thus, charcoal studies published in 2022 provide the lower-end range of the Pando's potential age---around 9,000 years old, while the somatic mutation models' most conservative estimate of 16,000 years old awaits replication using new material and methods, and will also require climate models to prove conditions were favorable to the Pando seed being able to germinate and establish itself during this period.
Estimates of Pando's age have also been influenced by changes in the understanding of establishment of aspen clones in western North America. Earlier sources argued germination and successful establishment of aspen on new sites was rare in the last 10,000 years and therefore, Pando's root system was likely over 10,000 years old. More recent observations, however, have shown seedling establishment of new aspen clones is a regular occurrence and can be abundant on sites exposed by wildfire. These findings are summarized in the U.S. Forest Service's Fire Effects Information System: