For generations, the Cherokee had gathered plants along the Buffalo River in Arkansas. The flora could be used to make a wide variety of things: blow guns, baskets, medicine and even ganatsi, a hickory nut soup.

Then, in 1972, the National Park Service took over the river and made it illegal to remove plants there without permission from the authorities.

The move cut off a valuable supply of river cane, bloodroot, sage and other plants, which can be difficult to find on the Cherokee Nation’s reservation in northeastern Oklahoma, on the border with Arkansas.

Last week, about 50 years after the river became federal land, the Cherokee received formal permission to gather those plants just as some of their ancestors did, thanks to an agreement between the tribe and the National Park Service.

The agreement, which was signed last week, lets the Cherokee citizens gather 76 types of plants along the river that are important to the tribe, according to the agency and the Cherokee Nation.

“This is an action that will last generations,” Chad Harsha, the tribe’s secretary of natural resources, said at a signing ceremony on April 20.

The agreement will be in effect for five years and can be renewed. An employee at the National Park Service came up with the idea for such a pact around 2014 and worked with researchers at the University of Arizona to propose the agreement to the Cherokee, said Clint Carroll, a Cherokee citizen and an ethnic studies professor at the University of Colorado Boulder.

Jenny Anzelmo-Sarles, a spokeswoman for the National Park Service, said that the Cherokee’s agreement with the agency to gather plants along what is now Buffalo National River had been “in effect” since November 2019, but the signing ceremony happened only last week because of delays caused by the pandemic.

This was the third such agreement that the agency has signed with a tribe, said Jennifer Talken-Spaulding, a cultural anthropologist at the agency.

The first was between the Tohono O’odham Nation and the Saguaro National Park in Arizona in 2018, and the second was in 2019 with the Eastern Band of Cherokee Indians and the Great Smoky Mountains National Park.

The agreement reverses a modicum of the centuries of Cherokee mistreatment by the United States, which Chuck Hoskin Jr., the Cherokee Nation principal chief, said at the signing ceremony had threatened the tribe’s language and culture.

In the late 1830s, the Cherokee were forced, along with four other tribes in the Southeast, to move west along what is now called the Trail of Tears, according to the National Park Service and the Cherokee Nation.

More than 4,000 Cherokee members died during the move, according to the Cherokee Nation. But some of the survivors settled for a time along the Buffalo River before they eventually ended up on the reservation, said Julie Hubbard, a Cherokee Nation spokeswoman. The reservation is about a three-hour drive from Buffalo National River in Arkansas, she said.

The Cherokee are among the largest tribes in the country, with more than 140,000 citizens living on the reservation.

Under the new agreement, Cherokee citizens can gather plants along the river if they register with the tribe, which will then notify the National Park Service, Mr. Harsha said.

Plants are sacred to the Cherokee and allow the tribe to maintain a connection to their land, Chief Hoskin said. Citizens gather them in small quantities that are sustainable for the land they grow on, said Dr. Carroll, the ethnic studies professor in Colorado.

National parks often have a more bountiful supply of plants than reservations, which are more prone to land development and rising temperatures, he said.

The Cherokee closely guard the methods they use to turn plants into medicines or supplies or food, Dr. Carroll said, because the techniques have been exploited and ridiculed by outsiders.

The reservation in Oklahoma is not the Cherokee’s original homeland, but the tribe has built a connection to the land over the last two centuries, Dr. Carroll said.

The agreement will ensure that future generations can learn the secrets of the sacred plants, which was more important than ever, Dr. Carroll said, because “with climate change, the plants aren’t guaranteed to be there.”