When President Trump’s new secretary of the interior Ryan Zinke rode a horse across the National Mall to the steps of his new office, there was cautious optimism, as a western congressman who professed to idolize Teddy Roosevelt seemed like a solid choice to govern 20% of the land base of the United States.

In the unforgiving milieu of Washington DC, Zinke and the “horse he rode in on” were subjected to withering ridicule. As the 18th director of the National Park Service (NPS), where I oversaw over 400 national parks and the equestrian patrol of the National Mall who accompanied the new secretary, I chalked it up to a publicity stunt.

But when Zinke had a new flag raised over the Interior Building, signaling to all there was a new sheriff in town, I knew we were in for some rough waters. Now that Zinke’s flag has been unfurled for the last time over the Department of the Interior, many of us who care deeply about our national parks and public lands have breathed a collective sigh of relief.

The secretary of the interior has a complicated and important job. He or she oversees all of the national parks, the national wildlife refuges, and the public lands of the Bureau of Land Management, plus the scientific work of US Geological Survey, and leasing and regulation of coal mining and oil and gas development in the oceans off the coast of the United States. He or she carries a trust responsibility to Native Americans and is the water master of the Colorado river. The secretary is the keeper of the nation’s history as the steward of the Statue of Liberty, homes of past presidents, civil war battlefields and our most powerful civil rights sites, such as the church of Dr Martin Luther King Jr.

At their best, past interior secretaries from both parties have found the right balance between conservation, preservation and development, bringing in science, public engagement and a stewardship view towards the future of our precious lands and waters. At their worst – embodied by James Watt, the secretary under President Ronald Regan who canceled a concert on the mall by the Beach Boys because they attracted the “wrong element” – science has been suppressed or ignored and resources that belong to the American people have been given away to those who saw only short-term profit.

Jonathan Jarvis listens to community leaders in Maine in 2016. Photograph: The Washington Post/Getty Images

While we were hopeful that Zinke would be one of the good ones, we were soon disappointed, then appalled. As he was surrounded by the staff of Gale Norton, secretary of the interior to President George W Bush, his doors were soon darkened by profiteers, big game hunters, oil executives, and climate deniers. Under Zinke’s flag, national monuments were carved up and reopened for development, exemplified by the reduction of Bears Ears national monument under the guise of a “review” under which Native American input was left out and public opposition ignored. Policies that planned for climate change’s impacts on national parks were rescinded, and leasing of public lands for development was accelerated (despite a glut of oil).

Career public servants, such as the superintendent of Yellowstone national park, were randomly moved to force their retirements, and others were threatened with either a forced reassignment or a complete elimination of their program. Climate scientists were told to edit their own research, eliminating any reference to human causes (but fortunately some refused).

Then Zinke rolled out a series of poorly conceived ideas: eliminate national park passes for the active military and fourth graders, increase national park entrance fees by several orders of magnitude, and require upfront payment for first amendment protests on the National Mall. Two years after he took the reins, the positions of director of the National Park Service and head of the US Fish and Wildlife Service remain vacant, unprecedented in history, leaving the two agencies rudderless and adrift.

Zinke’s flag has been lowered due to his own unethical excesses, but little will change at interior. In charge will be the deputy secretary David Bernhardt, the brains behind most of the unwinding of our national estate. As the acting EPA administrator Andrew Wheeler was to Scott Pruitt, David Bernhardt is to Ryan Zinke: smart, shrewd, low-profile and effective. When this all ends, what will be the lasting damage?

Millions of acres that were available for outdoor recreation will now be held by private companies for fossil fuel development. Many distinguished career public servants will be gone and many mid-level employees will be reconsidering their career choices. Regulations that protect our air, water and wildlife will be weakened and need rebuilding. And our options for addressing climate change will have been narrowed. The one thing that the Zinke administration cannot rewrite is history, and history will not be kind to his tenure.

There is good news besides his departure, and the legal challenges to many of his policies and actions, led by the conservation community. As I wrote in my book The Future of Conservation, I have faith in the rise in the millennial generation active for conservation. They are smart, diverse, innovative and fired up, forming not only resistance, but a movement that will stand up locally and nationally for the future of our parks and public lands for all, forever. Someone in this group will be a future secretary of the interior and they will be one of the good ones.

Jonathan B Jarvis was the 18th director of the National Park Service. Over his 40 years with the NPS, he served under 10 different secretaries of the interior. He is the co-author of The Future of Conservation in America, A Chart for Rough Water, from University of Chicago Press.