They are the ancient giants of America – towering trunks of sequoias or beech or ash that started to sprout in some cases before the age of the Roman empire, with the few survivors of a frenzy of settler logging now appreciated as crucial allies in an era of climate and biodiversity crises.

Joe Biden has vowed to protect these “cherished” remnants of old growth forest, as well as the next generation of mature forests, directing his government to draw up new plans to conserve the ecological powerhouses that enable US forests to soak up about 10 percent of the country’s carbon emissions, as well as provide a vital crucible for clean water and wildlife.​

Yet, the US Forest Service has not included mature trees in this new plan, which also includes loopholes conservationists say allow ongoing felling of trees that are hundreds of years old. The Forest Service, responsible for 154 national forests and nearly 25m acres (10m hectares) of old growth trees in the US, has also largely declined to conduct required reviews of multiple logging projects amid a stampede of tree cutting that threatens the oldest, richest trees before any new curtailments are imposed.

“The largest logging projects I’ve ever seen are targeting the last, best remaining old growth trees left in the country,” said Chad Hanson, a forest ecologist and co-founder of the John Muir Project.

Hanson said the Forest Service had failed to properly follow the president’s directive, instead allowing logging that imperils the remaining trove of the US’s long-lived, untouched trees.

“We have a rogue agency in the Forest Service that is trying to benefit the logging industry before reforms take place,” he said. “The situation is rampant as far as I can tell and it risks squandering a once-in-a-generation opportunity to protect these incredible forests.”

The Forest Service – which has defended its approach – approved 31 logging projects covering 116,460 acres of old growth forests just between December and April, a recent agency report states. A further 18 planned cutting projects within old growth forests are being considered.

In all, dozens of major logging projects are being advanced across the US, including the felling of 130,000 acres of old growth forest, an area roughly equivalent to the size of Chicago, in Plumas national forest in California; a plan to cut 95,000 acres in the Yaak River Valley in Montana that contains 600-year-old larch trees; and a program called the Telephone Gap project that aims to hack away a portion of ancient forest in Vermont that is 90 percent old growth and mature trees.

Many of these plans have been granted approval since Biden’s executive order in April 2022 that demanded his agencies take action to protect the most storied, grandest trees in the US. The overall amount of logging in national forests has surged 24 percent during Biden’s term, despite him committing, along with 144 other world leaders, to reverse deforestation by 2030.

The Forest Service has rejected the suggestion that it is allowing the timber industry to plunder older trees, pointing to reduced cutting rates compared with previous decades and a service policy to “protect, maintain and improve old growth forest conditions”. It also defended its policy on reviewing, saying all projects that fell under the scope of the mature and old growth requirement were looked at.

Critics, though, see an agency pushing through a rush of logging before outdated practices are overturned. “It’s insane, there’s just no justification for this,” said Hanson, who is part of a legal effort to prevent logging amid giant sequoias, a project ostensibly to protect a species that only grows in a 60-mile band along California’s Sierra Nevada. “Why would we log giant sequoias of any size? It’s just crazy.”

In response, environmentalists have launched legal action to stymie logging from New Hampshire to California, while tree-sitting protesters have occupied targeted woodland in Oregon. Scores of scientists have written to Biden warning that the outgoing president’s climate legacy is at risk and lamenting that “we have lost too many of those living witnesses of the past.” The “timber wars”, a fierce 1970s struggle over the future of forests that helped preserve the last fragments of old growth, appear to be rekindling, 50 years on.

“If the Biden administration wants this process to be something more than a greenwashing exercise, then it must put stronger pressure on the Forest Service,” said Zack Porter, executive director of Standing Trees, a Vermont conservation group. “Biden needs to intervene to live up to his climate goals, because at the moment this process is going off the rails.”

There are trees standing in America far older than the country itself. Perhaps the most famous of these, the gargantuan giant sequoias of California, can surpass the grizzled age of 3,000 years as they grow to a towering 300ft tall and slowly layer a bulk of several hundred tons, making them one of the oldest, as well as largest, organisms on Earth.

A bristlecone pine, also in California, is thought to be even more ancient, clocking in at around 4,800 years old. Other species in the US range in the hundreds of years old, having survived in plunging ravines or remote mountaintops from the ravages of axe and chainsaw.

Such timeworn trees were long seen as worthless. “They were viewed as old and decrepit and valuable for logging, not much else,” said Jim Furnish, a former deputy chief of the Forest Service, which was established in 1905 and has long had strong ties to the timber industry.

“If you cut down the older trees, you then get younger forests that can provide timber quickly,” Furnish said. “That was the rationale, which has left us with very little old growth.”

In recent decades, however, scientists have amassed evidence that older trees are treasure troves of life. They draw up and then expel moisture into the surrounding air like a sort of biotic pump, essentially creating their own weather systems, filtering water (national forests provide a fifth of the US’s clean water supply) and offering homes in craggy hollows to a panoply of wildlife.

As they grow, the trees’ bark thickens, making them and the surrounding forest more resistant to fire. A network of fungi helps spread a bounty of water and nutrients to the forest community. When these trees, having mopped up huge doses of carbon dioxide, eventually die, the toppled trunks regenerate soil, nourishing trees and animals around them.

“Their value is just off the charts,” said Dominick DellaSala, a veteran forest researcher. “You cut down a tree like that and you destroy habitat and lose 80 percent of that stored carbon into the atmosphere, more carbon than is lost from a fire. There’s just no reason to do it.”

A rethink on old growth followed a bitter battle over the imperiled northern spotted owl in the Pacific north-west, with millions of acres of the bird’s favored aged forest habitat ultimately set aside from cutting in 1994. The Forest Service points to a nationwide decline in logging since this time, with the agency considering wildfires, insect infestations and the climate crisis to now be the greatest threats to US forests.

Still, there has been an uptick in logging since Biden became president in 2021, with the Forest Service removing 2.94bn board ft (7.27m cubic meters) of timber from national forests last year, enough to fill more than 1.25m logging trucks, according to advocacy group calculations on agency data. The Forest Service still works towards “timber targets” that, it recently told Congress, it could increase with more resources and speedier environmental reviews.

The agency has a deep-rooted mindset of muscular “management” of forests rather than just letting them grow, according to DellaSala. “They will always argue for chainsaws and bulldozers, no matter what the issue is,” he said. There is plenty that could still be cut, too – just a quarter of the 112m acres of old growth and mature forests on Forest Service and Bureau of Land Management land is protected, DellaSala’s research has calculated.

Forests had long been selectively cut or burned by Native Americans but the arrival of European settlers kickstarted the widespread razing of trees for timber and farmland, to the extent that a mere 5 percent of original forest, scattered in small patches of trees, is left across the country. In the eastern US, barely 1 percent remains.

The Biden effort to stem losses of old growth trees, therefore, ignited optimism that a major turning point had arrived. “We have lost so much, there is such a deficit that we are recovering from,” said Sarah Adloo, executive director of the Old Growth Forest Network. “So just hearing the words ‘old growth’ from the president’s mouth was really wonderful.”

Biden ordered the Forest Service and the BLM, which collectively manage forests spanning about 250m acres, an estate about double the size of Spain, to conduct the first inventories of remaining old growth and mature forest and set about updating individual forest plans to curb their loss. “These forests are an essential partner in tackling climate change,” insisted Ali Zaidi, a senior White House climate adviser.

The timber industry, long used to procuring valuable wood from some of the largest, and therefore usually oldest, trees on public land, reacted with dismay. “We are extremely concerned about the disruption this unprecedented approach will have on urgently needed management efforts,” said Bill Imbergamo, head of the Federal Forest Resource Coalition, an industry group, citing the imperative, disputed by many scientists outside industry or government, to actively cut or “thin” forests to prevent insect outbreaks, or to reduce wildfire risk.

But environmentalists also saw flaws. There is no universal definition of old growth – some scientists class it as trees that have reached about 120 years in age – but there is agreement that mature trees, of about 80 years in age, must be protected to ensure more old growth in the future. The Forest Service plan, presented in December and recently updated with a draft environmental assessment, does not include mature trees, however, despite them covering more than double the area, about 68m acres, of old growth, according to the agency’s inventory of its managed land.

“If you allow mature trees to be cut, you get no additional old growth,” Porter said. The Forest Service plan, which is on track to be finalized in January, also allows the felling of old growth trees for purported environmental reasons, which could be used to justify further logging that many scientists say actually worsens fire and pests.

“It’s clear to me that the Forest Service is intent on promoting a new era of destructive commercial logging in old growth forests on public lands, while trying to deceptively spin it as wildfire management, forest health and community protection,” said Hanson. “Why isn’t President Biden telling the Forest Service no, and insisting that mature and old growth forests be fully protected from logging, as hundreds of scientists have urged?”

In December, Chris French, the deputy head of the Forest Service, did send an agency-wide memo requiring all logging projects that include old growth forests to be reviewed and approved by service leadership before proceeding.

However, when the Guardian asked the Forest Service about the status of 29 contentious logging projects across the US, the agency confirmed only five had been reviewed, with many rejected for assessment because of a supposed lack of old growth, or because the projects had started before the memo, even though such a constraint was not stipulated in the original edict.

A Forest Service spokesperson said mature forests were not included in the plan because climate change “introduces a lot of uncertainty” as to where older forests can survive. “The goal is not to manage all mature forest as future old-growth forest,” he said. “In some cases, places that are currently forests will no longer be forests. In others, the plants and animals will change dramatically. So, a strict preservation approach might not work.”

The spokesperson added that the service was “clearly harvesting much less timber” than it was in the period up to around 1990, when policies started to shift towards ecological needs and logging focused more on younger, plantation-based, trees.

He also denied that reviews of old growth logging projects were being overlooked by service leadership, or sidestepped by local forest managers. “All projects that fall within the scope of the mature and old growth requirement are reviewed,” the spokesperson said. “Forest projects are reviewed by both the regional and national offices, so it is unlikely that forests could ignore the direction.”

On a recent, steamy late-spring day, Porter led a small group through a section of the Green Mountain national forest, a 400,000-acre slice of rich northern hardwood forest in Vermont, a rare splash of older trees in a region denuded of original forest. Black bears, moose and beavers are found in this place, which has a touch of the prehistoric about it, with its gurgling streams, ferns and moss-covered boulders.

“These are big, big trees for the eastern US, there’s nothing much like this left,” said John Roe, a retired forest ecologist, as he surveyed the soaring stands of maple, ash and birch. “This sort of forest is of global importance.” The trees have rebounded since the US civil war era, when farmers abandoned the area. Give these trees another 160 years, Roe said, and you will see the sort of complex, intact forest there was before European arrival.

Many of these trees won’t get the chance to do so – the Forest Service is considering a logging program, called Telephone Gap, that will hew about 12,000 acres, an area slightly smaller than Manhattan, containing mostly mature trees with some old growth. “My worry is we foolishly sacrifice more than a century of recovery here,” said Porter.

If you trudge deeper into the heart of this national forest you get to a lake called the North Pond, an idyllic spot favored by beavers and fringed by slopes of trees, many that have never been cleaved. Clamber over some rocks and slippery moss into these stands and you can find sentinels that have stood amid this scene for timescales that leave the modern world behind.

Roe holds a tape measure to the bark of a grand yellow birch – 39in in diameter, probably 300 or so years old. A tree that was overlooking this lake, passing the seasons, before George Washington was born. “This is a monster,” Roe said, gawping up at the tree.

In March, Porter got an email from the district ranger overseeing the planned logging project, stating that there was “no need” for the plan to be sent to Forest Service leadership for a review as it would not disturb what the forest managers define to be true old growth, which is this tiny amount of pre-colonial woodland left behind.