Democracies rarely have famines of any significance (but their colonies or other unrepresented dependencies do). So should the famines of the USSR under Lenin/Stalin and the PRC under Mao be attributed to specifically communist rule or to dictatorial rule in general? That is, were there massive famines in other highly-populated non-communist dictatorships (like Pakistan, Brazil, or Nigeria during their periods of autocratic rule) -- or did the communist system itself produce them all out of proportion to other types of autocratic rule? I ask only because I'm trying to evaluate the accuracy of statistics attributing massive numbers of deaths to communism in particular (see, for example, the folks over at Victims of Communism, who argue that more than 100 million were killed by communism over the last century, a claim that rises or falls based on the attribution of famine deaths to communism).
Certainly there have been widespread famines under non-communist regimes. The British Empire is a prime example; see the history of the Irish potato famine, or famines in colonial India (Mike Davis, Late Victorian Holocausts would be a good place to start). Amartya Sen's work on the political causes of famine would probably also be of interest (start with "Poverty and Famines"). For Nigeria specifically, there was a widespread famine related to the Biafran War.
That doesn't mean that famines can't be attributed to communism--or, at least, to the specific communist regimes that existed in the USSR and China. It just means that other (non-democratic) regimes have also caused famines. Sen would certainly say that autocracy itself is the problem, and would include imperialism as a type of autocracy.