The predictions of a bad year for Lyme disease are based on several factors, one of which is El Nino. The deer tick feeds on these mice. In a typical large forest, hardwoods will be in certain areas, and species like pine will predominate in other areas.
Deer range through both types of areas, along with their associated ticks.
Deer do not serve as good reservoir hosts for Lyme disease, so if they are far from the oak forests where the mice live, they are less likely to be infected. Mast years occur every 3-4 years. Winter temperatures may have some effect, but other factors also appear to be at work. When there is a mast year, the mouse population increases dramatically, and the deer also move into the hardwood groves to eat the acorns, whereas they might ordinarily be in other parts of the forest. That means lots of mice, lots of deer, and lots of ticks converge in hardwood groves during mast years.