Dorothy Johnson has been a bedrock volunteer in rural Braham, Minn., since she retired from finance in 1997. She helped raise money for the new $2 million community center and has been volunteer treasurer of her church and the local food shelf for more than 15 years. Now, at 84, Johnson is ready to hand over the reins.

But attracting a solid base of younger helpers in her town of 1,800 has been tough.

Reliable, longtime volunteers, who were shaped by the Great Depression and WWII, are dying or getting too old to do the work. Baby boomers aren’t stepping in to fill their shoes — at least not in the same way.

“The people doing the volunteering are elderly,” Johnson said. “We can’t get the new ones because they have to continue to work and support themselves.”

Many boomers are working beyond the traditional retirement age, and have little time to give. That’s not the only issue, however.

They’re willing to volunteer, but they want flexibility, work that taps into their skills and evidence that they’ve made a difference — not things previous volunteers needed.

“Everyone is scrambling,” said Mary Quirk, executive director of the Minnesota Association for Volunteer Administration. “Boomers and millennials are looking for something different from what organizations are providing.”

Food shelves are the first to feel the crunch, but charities and nonprofits across the state are facing the same challenge.

Today’s aging volunteers are the last of a wartime generation defined by loyalty, sacrifice and service. They’ve shown up week after week, year after year, to do whatever was asked of them, expecting little in return.

“We have these hard-core volunteers — you can set your watch by them,” said Rich Smith, executive director of Family Pathways, which operates food shelves and thrift stores in Minnesota and western Wisconsin. “All of them seem to be in their mid-70s and older. It doesn’t seem as if the 60-somethings are coming in behind them.”

Unlike the generation before them, boomers don’t want to be chained to a schedule or tied to one organization. They want the freedom to jump from cause to cause or take months off to travel.

“Part of the puzzlement with boomers is people don’t want to commit as long as they used to, and that’s hard for organizations to handle,” Quirk said.

Recruiting and retaining younger volunteers is equally challenging.

Generation Xers are juggling families and careers. High school students are more likely to take on one-time or short-term service projects, squeezed between after-school social activities and sports.

The concept of a volunteer’s “return on investment” is especially important to millennials, who were born after 1980, said Sarah Sladek, a consultant who helps businesses and nonprofit groups understand generational differences.

“For younger people, it needs to be proven that their time is making a difference, and that they are getting something for their time,” said Sladek, who added that projects for such groups as Habitat for Humanity appeal to millennials. “This is the trophy generation, so even the experience of volunteering has to be ‘awesome.’ ”

A double whammy

Despite recent declines, Minnesota continues to have one of the highest rates of volunteerism in the nation.

About 70 percent of residents do “informal volunteering,” such as helping out neighbors, and almost 36 percent give their time to school, civic and charitable organizations, according to the Wilder Foundation and the Corporation for National and Community Service.

But with nearly a third of baby boomers planning to volunteer when they retire, it’s increasingly clear that nonprofits need to figure out how to tap into boomers’ time and expertise. Nonprofits also need to build a cadre of younger volunteers to help provide services aging boomers will need.

Recently, Minnesota became one of 11 states to receive a $200,000 federal grant to do just that.

Initially, the grant will focus on food shelves, which rely heavily on volunteers.

Some hunger-relief groups are already changing the way they do business. Meals on Wheels seeks out corporate volunteers and promotes its work as something families can do together. Pillsbury United’s food shelf in Minneapolis emphasizes the educational component by encouraging volunteers to develop recipes and hold taste tests to encourage healthier meals. The food shelf in Willmar, Minn., uses Facebook and Twitter to connect with potential volunteers.

“We have to think about different ways of doing our work so people can get food no matter where they live, ”said Patrick Rowan, executive director of Metro Meals on Wheels.

In Braham, Johnson and other aging volunteers are doing what they can. They’re tapping local churches to provide food shelf workers each Thursday and are trying to put out the word to the next generation. But the secondhand store that funds the four-county food shelf also relies on volunteers in their 70s and 80s, and Johnson fears that time is running out.

“There’s a lot of joy you can get from it [volunteering],” she said. “We need to start getting replacements — and training them.”