Studies over the last couple of decades of human zoonotic (animal reservoir initiated) epidemics reveal that vulnerability-factors for such epidemics include high population densities, human-induced changes in the biological makeup of ecological systems, and the distinct human interactions within these new ecosystems, intensive farming practices, malnutrition, and prior ill-health. The recent DNA evidence of Yersinia pestis, known to be responsible for the bubonic plague, forces a re-evaluation of basic assumptions of the Black Death that almost all historical narratives have made. A monomorphic pathogen, Y. pestis, has been remarkable in how little it has changed since the Black Death, and there is no evidence to show that the 14th-century plague was more virulent or contagious than modern outbreaks.
Contemporary medieval documentation reveals a perception that the Gaelic-Irish were not suffering from the Black Death as much as the colonists. However, if the genetic disposition between the national groups was a significant factor, then why is there no noteworthy difference noted in subsequent epidemics? This paper uses vulnerability factors for a zoonotic epidemic to assess regional ecological risk in Gaelic and colonial Ireland. Since the ecological change of the period has been largely attributed to human activity, socio-economic and knowledge systems and institutions role in promoting certain activity that altered the landscape is an important part of this inquiry. Pollen evidence is used in conjunction with historic and archaeological data to note regional differences, and to document how they became especially apparent during the Bruce Invasion of 1315–1318. The evidence suggests that vulnerability to epidemic disease was greater in the south-east and midlands of Ireland than in northern parts of the island, and that this paved the way for contrasting responses to the Black Death.