Consumer spending on Long Island surged last month as residents snapped up post-holiday bargains and used gift cards received in December.

Sales-tax collections, a barometer of spending, rose 7 percent in January compared with a year earlier. They were up 9.1 percent in Nassau County and 5.1 percent in Suffolk County, the state Taxation and Finance Department said Wednesday.

The increases follow year-over-year declines in December 2012, which had alarmed some economists because they coincided with the crucial holiday shopping season. Sales-tax collections were off 1.9 percent compared with December 2011.

"What this shows is the holiday selling season has shifted to include January because of bargain hunters and gift cards," said Pearl Kamer, chief economist for the Long Island Association business group.

She added, "You are seeing a new trend: People wait until they can get a bargain, they buy something for themselves that they might like, and they use their gift cards."

However, Kamer and others said spending gains don't always translate into higher profits for retailers, because many purchases were spurred by discounting. Kamer predicted local consumers would "pull back" this month or in March as gift cards are exhausted and credit-card bills come due.

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She said January's sales-tax report does not signal an upturn in Long Island's economy. "This isn't a reflection of the economy; this is a reflection of the changing nature of holiday spending," she said.

Tax collections also were up in January 2012: They climbed 1.3 percent Islandwide from a year earlier.

Irwin Kellner, chief economist at the MarketWatch business information service and a former Hofstra University professor, called the tax data "anemic" because the year-over-year increases diminished as 2012 progressed.

Asked if the local economy was improving, Kellner said, "I wouldn't draw that conclusion. Until you see significant job growth, you cannot expect to see significant growth in spending."

He warned that consumers may open their wallets less frequently later this year as property taxes rise, gasoline prices remain in the stratosphere and medical care becomes more expensive.

The sales tax helps to fund state and county governments, and the Metropolitan Transportation Authority.