The first wave of boomers—now 55 to 64 years old—with at least $100,000 to invest have become significantly more cautious since 2006, according to the 2011 Investor Brandscape Report by Cogent Research.

These boomers reported holding 15% of their investable assets in “high-risk investments” compared to 24% in 2006. That’s one reason their holdings, including savings in retirement accounts, have fallen, on average, to $708,000 from $809,000 four years earlier.

“They’ve made a dramatic shift in their allocations in just the last few years,” said Cogent senior project director Meredith Lloyd Rice in a telephone interview. About a third of the group are fully retired.

Even so, she says “we’d expect their assets to be growing.”

Cogent Research surveyed 4,000 consumers with at least $100,000 in investable assets in October, 2010 and October 2006.

Second-wave boomers—now 45 to 54—also say they’ve grown more cautious; this group reported holding 24% in “high risk investments” down from 32% in 2006.