UPDATE 2-Packaging Corp of America earnings beat estimates

* Q1 EPS of 25 cents beats estimate of 19 cents

* Sales down 11 pct

* Sees Q2 earnings below expectations.

* Stock up 12 pct in trading after the bell (Adds analyst comments, details, updates share movement,)

NEW YORK, April 20 (Reuters) - Packaging Corp of America (PKG.N) reported higher-than-expected first-quarter earnings on Monday, helped by lower costs, but forecast a second-quarter profit short Wall Street estimates.

Shares of the company rose 12 percent in trading after the bell.

"The stock is up because people like the earnings -- because of this beat it might add a few cents to people's full-year earnings estimates," analyst Joshua Zaret of Longbow Research told Reuters.

Net income in the quarter fell to $26 million, or 25 cents a share, from $32 million, or 31 cents a share, a year ago.

Net sales dropped 11 percent to $512 million.

Analysts, on average, expected earnings of 19 cents a share, on revenue of $538.7 million, according to Reuters Estimates.

However, the company forecast second-quarter earnings to be about 15 cents a share, below analysts' estimate of 16 cents a share.

"Our second-quarter earnings will be impacted primarily by lower selling prices resulting from previously published changes in prices for containerboard," Chief Executive Paul Stecko said in a statement.

Packaging Corp is one of the largest U.S. producers of containerboard, which is the type of paper used to make corrugated boxes.

Longbow's Zaret said the real challenge for the company is going to be the next couple of quarters when the tail winds turn into headwinds, particularly on the pricing front.

"Containerboard prices have been eroding since December and that price erosion is going to find its way into boxes during the current quarter. And I think that's going to be the biggest effect on their earnings."

Packaging Corp closed down 7.3 pct at $12.82 Monday on the New York Stock Exchange, but after the bell traded at $14.35. (Reporting by Hezron Selvi; Editing by Steve Orlofsky)