CANBERRA, Oct 4 (Reuters) - A little over half of Australia's farmers expect the country's agricultural output to grow over the next decade, according to a survey published on Wednesday, with optimism in short supply among livestock farmers particularly.

Australia is one of the world's most important agricultural exporters, shipping products including wheat, beef, wool and cotton to global markets.

After widespread flooding last year, the weather has turned hot and dry, damaging some crops and forcing farmers to sell livestock.

A survey of 1,600 farmers by the National Farmers Federation (NFF) and communications agency Seftons pointed to frustration with issues including the pricing power of supermarkets, environmental laws and poor infrastructure.

It echoed a poll by Rabobank last month which found that farmers were worried about falling commodity prices and a return to drought and 51% thought the agricultural economy would worsen over the next year.

The NFF survey found that 55.8% of farmers thought Australian production of food and fibre would increase over the next decade and less than half -- 45.6% -- thought the future of the family farm was bright.

Some sectors were more optimistic than others. Some 55.8% of fruit and vegetable farmers and 55.4 of sugar growers felt more positive than a year ago but only 26.6 per cent of beef producers and 30% of sheep farmers felt more positive than this time last year.

The NFF said workforce shortages were also slowing farm productivity, with 87.2% of poll respondents saying they would increase their labour force if hiring conditions improved.

"Farmers are feeling frustrated," the federation quoted its president Fiona Simson as saying.

"They're being squeezed by a lack of government support on a wide range of fronts -- whether that's the unchecked market power of supply chain players, crumbling rural roads, unnecessary green tape, workplace laws ... the list goes on."

(Reporting by Peter Hobson; Editing by Simon Cameron-Moore)