John Tester grew up in Gibbon, Minn., tagging along each summer with conservation researchers restoring oak savannas in the area.

But Tester, then about 9, wasn't satisfied with just watching. He helped the scientists plant bur oaks in an effort to revive part of southern Minnesota's native biome.

"He just had a curiosity and love of the outdoors and nature," said his son, Peter, deputy commissioner of the Minnesota Pollution Control Agency. "It was just in his blood from when he was a young boy."

Tester would later become a pioneering ecologist and professor at the University of Minnesota whose research took him around the globe and who wrote a groundbreaking book on the state's ecology, "Minnesota's Natural Heritage," that will be rereleased next year on its 25th anniversary. Tester died of age-related health issues on Nov. 16, two days before his 90th birthday.

Tester graduated from the U and returned in 1957 to work at the Bell Museum. In the early 1960s, he was part of a team of university scientists who became the first in the world to track radio-collared animals in real time.

Their breakthrough accomplishments revealed for the first time how far animals like deer and fox wandered in a day, how deep gophers burrowed underground and where fish swam in the waters of the university's Cedar Creek Ecosystem Science Reserve.

"We would have coffee in the morning and come up with an idea and say, 'Oh, that sounds like a great idea! Let's do that!' " recalled Donald Siniff, who was part of the team. "Everything was new."

Tester's research from that era has been cited in scientific journals as recently as 2010, said Emilie Snell-Rood, an associate professor in the U's Department of Ecology, Evolution and Behavior. Tester helped found the department, where he taught for decades. "He certainly contributed to elevating the university and the department to where it is now with respect to the biology, the ecology work," Snell-Rood said.

He was an early advocate throughout his career for many practices that were novel at the time, including collaboration between scientists and using controlled burns to maintain prairies and forests.

He was also early to raise the alarm about global warming, said his former colleague, Dave Tilman, an ecology professor at the U and director of the Cedar Creek Ecosystem Science Reserve.

Tester and his wife, Joyce, raised their two sons in Minneapolis and North Oaks and then moved to St. Anthony Park. Joyce Tester said she was drawn to Tester's intelligence and appreciation of the arts while both were graduate students at the U.

"He gave his full attention to whoever it was he was interacting with," she said. "I was just impressed with his gentle manner."

Tester's other son, Hans, became an actor after earning his medical degree. He stars in Amazon's "The Man in the High Castle" and has had several TV and movie roles.

After John Tester's mother died, Hans Tester discovered a stack of playbills documenting all of the high school plays his father had starred in.

"Here he was — he had done all the leads in the all the high school plays, and did he ever tell me that, ever?" Hans Tester said. "I never knew! He said, 'Oh well … I didn't want to brag about it.' "

Tester is also survived by two grandchildren, a niece and a daughter-in-law. A celebration of Tester's life is scheduled for 3 p.m. Saturday, Jan. 11, at the American Swedish Institute, 2600 Park Av., Minneapolis. Donations can be made to the university's John Tester Itasca Research Fund.