The authors of the first chapter in Protecting the New Jersey Pinelands (B. R. Collins, N.F. Good, and R. E. Good) provide a good explanation of the relationship between the dwarf pitch pines and fire. In the pine plains, the dwarf or pigmy pitch pine has adapted to fire in that the seed bearing cones are closed or serotinous. These “serotinous” cones open only in high heat of the sort that occurs during a fire.
The distinctive character of this dwarf forest is probably the result of very frequent fires over hundreds or even thousands of years. Under such conditions the tree oaks, which are not found in the dwarf forest, would not have been able to maintain themselves, because they bear viable seed only on stems twenty years or more in age. The pitch pines present in this forest are genetically differentiated from other populations of the species. They are less upright, of shorter growth form, and produce cones at an earlier age. Unlike other pitch pines, whose cones open top disperse seed normalyy at maturity, the pitch pines growing in the dwarf forest have closed (or serotinous) cones that open to dispers seed only at high temperatures, such as those occurring during a fire (B. R. Collins, N.F. Good, and R. E. Good “The Landscape of the Pine Barrens”, p.15, in Protecting the New Jersey Pinelands: A New Direction in Land-Use Management edited by B.R. Collins and W.B. Russell, New Brunswick NJ: Rutgers University Press. 1988).
See this link for images of the pine plains taken just after a fire, along with images of growth after the fire.
A more detailed description of the pitch pine, including sections on fire ecology, is found on this usda webpage.