in the Darling Downs in the 1840s, squatters and pioneering families established cattle stations up until the 1870s, as far north as the Gulf Country. The early settlers of Queensland faced many problems, including a lack of labour, a lack of transport facilities to markets, attacks by Aboriginals, a climate that was too wet, drought and falling commodity-prices. An Australia-wide trend towards recession hit Queensland particularly hard from July 1866. Immigration faltered, unemployment rose and business activity contracted. It was not long before gold discoveries signaled a turnaround in Queensland's economic activity. Gold was discovered in the state in 1861 at Peak Downs near Clermont and in 1867 at Gympie. Many gold miners left the Victorian goldfields in the 1870s - surface gold had become scarce in that state - and moved to Queensland to try their luck. During the American Civil War (1861-1865) a shortage of cotton in Europe caused a cotton boom in Queensland. Copper was discovered at Cloncurry in 1869. In 1863 the first sugar-cane plantation was established and the first South Sea Islanders, referred to as kanakas, arrived, providing cheap labour - compare blackbirding. The sugar-cane industry expanded northwards along the coast with a plantation and mill operating at Innisfail in 1881 and in the following year a mill opened in Bundaberg. By 1890 developments in refrigeration technologies had opened new markets for types of produce which would previously have spoiled on the two-month-long journey to England. During the early 1880s the Dingo Fence was constructed to protect livestock in south-east Australia. It protected southern Queensland, aiming to stop attacks on sheep from Australia's native dog. The fence was maintained up until the 1970s. experts estimated that $60 million in losses occurs annually in Queensland due to dingoes that have penetrated the barrier. In 1886 the introduced rabbit crossed into southern Queensland, causing yields from pasture production to decrease. The rabbit also contributed to soil erosion through overgrazing. 20th century A drought in 1902 drastically reduced agricultural productivity. By 1906, maize covered 25%, sugar cane 23.8% and wheat 20.5% of cropping land in the state. In 1908, 700 bores were supplying artesian basin water to western Queensland, transforming an otherwise mostly arid landscape into a more productive area. Refrigeration and regular steamer services between Brisbane and London allowed Queensland to become Australia's largest exporter of meat in the same year. The Franco-British Exhibition of 1908 was