Commercial real estate professionals are traditionally an upbeat bunch.

To make it in the rough and tumble property market, you need to have a positive outlook.

So why are so many real estate players in a new nationwide poll sounding a bit glum?

Almost 60 percent of commercial real estate pros recently surveyed by accounting giant Grant Thornton LLP said they were pessimistic about the U.S. economy.

And almost half of the commercial property players polled said they are down on their industry's business outlook, Grant Thornton said Wednesday.

Two years ago, when the last such survey was done, only 5 percent of respondents were worried about the industry's outlook.

"A lot of that is the impact of the credit crunch," said Alvin Wade, who's in Grant Thornton's Dallas office.

"Its tentacles are stretching out and affecting a lot of industries – particularly real estate.

"With real estate usually being so highly leveraged, when the capital starts to dry up, that tends to make people more pessimistic."

In the latest survey, almost 70 percent said they expect unemployment rates in their markets to rise during the next year.

And 61 percent predicted that commercial building vacancy rates would go up.

Overall, the state of the national economy – no surprise – was the biggest concern cited in the nationwide survey.

The poll included responses from commercial property developers, owners and investors.

Despite the overall gloomy tone noted in the report, only 12 percent of real estate professionals say they had a negative expectation about their own company's outlook.