An old-growth forest in BLM California's Eagle Lake Field Office. Photo by retired BLM forester Don Dockery

Mature and Old-Growth Forests

Older forests have characteristics that can provide important wildlife habitat, contribute ecosystem services such as clean water and carbon storage, and harbor significant social and cultural values for many human communities. The U.S. Forest Service has defined old-growth forests since the 1980s, and the BLM relies on these regional definitions when managing old-growth forests on public lands. 

Old-growth forests are dynamic systems distinguished by old trees and related structural attributes. Old growth encompasses the later stages of stand development that typically differ from earlier stages in a variety of characteristics, which may include tree size, accumulations of large dead woody material, number of canopy layers, species composition and ecosystem function. 

Climate change has spurred more frequent and longer lasting disturbances in forest ecosystems, including wildland fire, severe drought, and insects and disease. Increasing the area of old-growth forests in the United States would contribute to the climate resilience and landscape health of public lands. To meet this objective, the BLM and U.S. Forest Service are putting further emphasis on management to promote the mature stage of forest development.  

Mature forests are defined ecologically as the stage of forest development immediately before old growth. The mature stage generally begins when a forest stand moves beyond self-thinning, and is often marked by abundance of large trees, vertical canopy layers, aboveground biomass accumulation and stand height, as well as other attributes. Mature forests vary widely in character with age, geographic location, climate, site productivity, relative sense of awe, characteristic disturbance regime and the values people attribute to or receive from them. 

Executive Order 14072

On April 22, 2022, the Biden Administration released Executive Order 14072: “Strengthening the Nation’s Forests, Communities and Local Economies.” The executive order directs the BLM and U.S. Forest Service to inventory mature and old-growth forests and analyze reforestation opportunities, among other measures to ensure the resilience of America’s forests. 

An initial national inventory of mature and old-growth forests on BLM and U.S. Forest Service lands was released on April 20, 2023, along with working definitions that provide quantitative measurement criteria for different forest types. The inventory and definition framework are the result of a year-long scientific effort by an interagency technical team, which included multiple engagement opportunities with Tribes, the public, stakeholders and agency employees. 

The majority of mature and old-growth forests managed by the BLM are pinyon and juniper woodlands

The BLM manages 19 million acres of pinyon and juniper woodlands, of which about 6 million acres are estimated to be old-growth. The BLM and U.S. Forest Service define old-growth pinyon and juniper woodlands to be 150-250 years old, depending on site productivity, the geographic location and other factors. Some juniper trees can exceed ages of 1,500 years, and pinyon trees more than 900 years. 

The following chart presents the initial inventory of mature and old-growth forests on BLM lands only by BLM State Office Administrative Unit: 

State Young Forest Acreage Mature Forest Acreage Old-Growth Forest Acreage
Alaska* 695,914 1,227,212 881,386
Arizona 393,137 803,139 285,081
California 988,652 407,856 66,461
Colorado 2,030,061 1,977,263 748,373
Eastern States 22,987 9,940 0
Idaho 338,844 521,710 50,580
Montana 979,083 358,137 86,152
New Mexico 1,642,672 887,440 350,679
Nevada 2,044,770 3,002,523 1,481,679
Oregon 1,909,382 1,140,928 626,349
Utah 1,572,171 1,980,682 3,557,563
Wyoming 595,078 381,945 123,953

*The initial inventory does not include all BLM-managed lands in Alaska. The inventoried area excludes 27.5 million acres of potentially forested land managed by the BLM in Alaska that is not included in the U.S. Department of Agriculture’s Forest Inventory and Analysis Program. 

Healthy, resilient forests are critical to helping the BLM respond to the climate impacts being felt by communities across the country because they store carbon, provide clean air and water, and sustain biodiversity. The work we complete under Executive Order 14072 will enhance the BLM’s efforts to protect and grow forests by creating a scientific framework for further study and public engagement on effective forest management and protection.