The Decline of Forests in America: Causes, Consequences, and Paths to Recovery

American forests are among the most productive and biodiverse ecosystems on the planet. From the old-growth conifers of the Pacific Northwest and spruce–fir forests of New England, to the longleaf pine savannas of the Southeast and mixed hardwood stands of the Midwest, forests in the United States support wildlife, store carbon, filter drinking water and anchor local economies built on tourism, recreation, and sustainable wood products.

Yet over the last century, many of these forests have shown signs of strain and decline. Climate change, more extreme weather, mega-fires, invasive pests and diseases, and unsustainable human activity are reshaping forest landscapes at a pace that is difficult to ignore. In this article we look at the main drivers behind the decline in forest health in America, what this means for biodiversity (including understory plants such as forest ferns), and the growing movement to restore and replant resilient, multi-species American forests.

Climate Change and Forest Stress in the United States

Climate change is one of the primary drivers of the decline in forest health in America. Rising average temperatures, more frequent heat waves, shifting precipitation patterns, and longer droughts all place trees under chronic stress. In many regions, summers are hotter and drier, winters are less predictable, and growing seasons are changing.

Stressed trees are less able to defend themselves against insects and diseases. A prolonged drought, for example, can weaken ash trees, oaks, maples, and conifers, leaving them more vulnerable to bark beetles, borers, fungi and root rot. Climate change also alters the timing of seasonal events such as budburst, flowering and leaf fall. When the timing of these events shifts, it can disrupt relationships between trees and the wildlife that depend on them for food, nesting, and shelter.

Changing Forest Zones and Species Ranges

As temperatures rise, the “climate envelopes” suitable for different tree species move uphill in elevation and northward in latitude. High-elevation spruce–fir forests in the Appalachians, for example, have limited room to move, while low-lying coastal forests may face both increased heat stress and sea-level rise. Some species can migrate or regenerate in new areas, but others are effectively trapped on mountaintops, peninsulas, or fragmented forest islands surrounded by development.

Over time, these shifts can change the dominant tree species in a region and gradually transform entire forest communities. The decline of certain iconic species—such as American chestnut in the past or ash trees today—can ripple through food webs, affecting everything from soil fungi and understory plants to birds and mammals.

Wildfires: From Natural Process to Mega-Fire Threat

Wildfires are another significant threat to the health of American forests. Fire itself is not new; many U.S. forests evolved with periodic burning. Historically, low- to moderate-intensity fires helped recycle nutrients, thin overcrowded stands, and maintain fire-adapted species such as ponderosa pine and longleaf pine.

The problem today is that wildfires in many regions—especially in the American West—have become more frequent, larger, and more intense. Decades of aggressive fire suppression allowed fuels (dead wood, dense young trees, and dry litter) to accumulate, while climate change has brought hotter, drier conditions and longer fire seasons. When a fire does ignite, it is more likely to become a fast-moving, high-severity blaze.

These mega-fires can destroy entire forest landscapes, burn deep into soils, damage seed banks, and leave behind hydrophobic, erosion-prone slopes. They also release enormous amounts of stored carbon back into the atmosphere, reinforcing the very climate changes that helped fuel them.

Prescribed Fire and Fire-Adapted Forests

To reduce the risk of catastrophic wildfires, land managers increasingly turn to prescribed fire—carefully planned, low-intensity burns conducted under controlled conditions. These burns mimic natural fire regimes, reducing accumulated fuels and promoting fire-adapted plant species.

In pine savannas, oak woodlands, and certain Western conifer forests, periodic prescribed burns can improve forest structure, open up the understory, stimulate the growth of fire-tolerant grasses and ferns, and increase overall resilience. Used alongside selective thinning and climate-smart planting, prescribed fire is one of the most effective tools we have to help American forests adapt.

Pests, Diseases, and Invasive Species in American Forests

Pests and diseases are also major contributors to the decline in forest health in America. In the last century, the U.S. has experienced wave after wave of introduced insects and pathogens: chestnut blight, Dutch elm disease, hemlock woolly adelgid, emerald ash borer, sudden oak death, and many others.

Many of these invaders arrive accidentally through global trade—hidden in wood pallets, nursery stock, or packing materials. Once established in a new region, they may spread rapidly through forests with trees that have little or no genetic resistance. Entire species or genera can be decimated in a few decades, leaving gaps in canopies and altering forest composition for generations.

The Emerald Ash Borer and Sudden Oak Death

The emerald ash borer has killed millions of ash trees across the Midwest, Northeast, and mid-Atlantic, transforming city streets, rural woodlots, and riparian forests once dominated by ash. Similarly, sudden oak death, caused by an introduced pathogen, has had devastating impacts on tanoaks and oaks in parts of California and Oregon.

When a foundational tree species disappears, other organisms that depend on its acorns, leaves, bark, or canopy may struggle to adapt. The loss of shade and root structure can also increase erosion, alter stream temperatures, and open the door to invasive shrubs and vines that further degrade forest health.