Before the act of union of 1801 the Irish parliament, although pretty ineffectual, did block food exports during times of crisis. Even in the year of slaughter 1740 when a short term famine was caused by climate change food exports were stopped by a combination of local officials and angry citizens. The difference in the 1840s was the presence of a large number of troops who protected food exports at gunpoint. It is nonsense to suggest that an independent Irish State would have continued to export food in these conditions: it wouldn't have lasted a week.