By Gernot Heller

BERLIN (Reuters) - Germany's BGA trade association slashed its 2016 forecast for export growth, its head said on Monday, predicting sales abroad by Europe's biggest economy would later stagnate as the delayed impact of Brexit hit home.

Global demand for German goods has slowed significantly, with Britain's decision to leave the European Union among several factors increasing uncertainties and complicating investment decisions, Anton Boerner said.

"The repercussions (of Brexit) will impact us massively in the near future," he told Reuters in an interview.

That effect had yet to be felt in the export sector, which the association forecast in April would grow by 4.5 percent this year.

"I (now) think growth of only between 1.8 and 2.0 percent is feasible this year," Boerner said.

Exports - traditionally the main driver of Germany's economy - had increased by 6.5 percent as recently as 2015, but Boerner said the outlook beyond 2016 was bleak.

"Exports are set to stagnate, possibly as early as 2017 if viewed pessimistically," Boerner said. "We're hitting the ceiling."

Germany releases trade figures next week for July, which are likely to show the first clear evidence of fallout from Britain's June referendum vote.

German exports to Britain, its third most important market, stagnated year on year in the first six months at around 44.8 billion euros ($50.1 billion).

UNCERTAINTY ELSEWHERE TOO

Further afield, Germany's trade prospects are also clouded by uncertainty about the U.S. presidential election, the rise of nationalist movements in Europe, and other crises including the failed July 15 coup in Turkey and the civil war in Syria, Boerner said.

Exports to the United States and France, Germany's two biggest markets, fell 4 percent to 53.4 billion euros and 2 percent to 52.1 billion euros respectively in the first half.

Demand from emerging markets was subdued, with exports to China only inching up 1 percent and Brazil falling by almost a fifth.

Strong demand from other EU countries drove export growth in 2015 and, overall, net foreign trade contributed 0.2 percentage points to gross domestic product growth of 1.7 percent.

The government and Germany's central bank predict the same growth rate this year, helped by soaring domestic demand, while exports are already not expected to contribute much.

($1 = 0.8950 euros)

(Reporting by Gernot Heller; Writing by Michael Nienaber; Editing by Joseph Nasr and John Stonestreet)