The clearance of the indigenous forest for the distillation of spirits, tanning and agricultural development began to lead to shortage of wood by the 1680s. The numbers of rats and goats had reached plague proportions by the 1690s, leading to the destruction of food crops and young tree shoots. Neither an increase on duty on the locally produced Arrack (drink) nor a duty on all firewood helped reduce the deforestation whilst attempts to reforest the island by governor John Roberts (1708–1711) were not followed up by his immediate successors. The Great Wood, which once extended from Deadwood Plain to Prosperous Bay Plain, was reported in 1710 as not having a single tree left standing. An early mention of the problems of soil erosion was made in 1718 when a waterspout broke over Sandy Bay, on the southern coast. Against the background of this erosion, several years of drought and the general dependency of St Helena, in 1715 governor Isaac Pyke (1714–1719) made the serious suggestion to the Company that appreciable savings could be made by moving the population to Mauritius, evacuated by the French in 1710. However, with the outbreak of war with other European countries, the Company continued to subsidise the island because of its strategic location. An ordinance was passed in 1731 to preserve the woodlands through the reduction in the goat population. Despite the clear connection between deforestation and the increasing number of floods (in 1732, 1734, 1736, 1747, 1756 and 1787) the East India Company’s Court of Directors gave little support to efforts by governors to eradicate the goat problem. Rats were observed in 1731 building nests in trees two feet across, a visitor in 1717 commenting that the vast number of wild cats preferred to live off young partridges than the rats. An outbreak of plague in 1743 was attributed to the release of infected rats from ships arriving from India. By 1757, soldiers were employed in killing the wild cats.
Question: How many years after governor John Roberts left office was an ordinance passed to preserve the woodlands through the reduction in goat population?
Answer: 20