Executives from discount-chain operator Dollar Tree Inc. said they expect that sales in the third quarter will be at the low end of the company’s forecast. They said long-term unemployment, high gas prices, and uncertainty over the upcoming US elections are factors in the quarterly sales results. In August, the Chesapeake, Va.-based discount chain had predicted revenue would be in the range of $1.71 billion to $1.75 billion for the third quarter. The news about the expected sales results came up during a presentation at Dollar Tree’s annual capital markets conference on Thursday. Dollar Tree operates more than 4,500 stores in the United States and Canada. Its stores sell merchandise priced at $1 or less.