The composition of the flora of the pine barrens is largely determined by fire frequency. Pitch-pine-dominated forests are the characteristic forests of this ecoregion, but where fires occur at intervals of 10 years or less, dwarf pine forests develop. Where fires are infrequent, oak-dominated forest develop. In wetland areas grow cedar swamp forests and hardwood swamp forests.
Pine-dominated forests
Pitch pine is the most abundant tree here. Shortleaf pine is also present, but not as abundant. In the southern regions of the New Jersey Pine Barrens, loblolly pine and pond pine are present and fairly commonly encountered. A variety of oaks grow among the pines, including black, white, post, chestnut, scarlet, and blackjack. These forests tend to be open with widely spaced trees and plenty of sunlight reaching the forest floor. The understory is thick with shrubs, including black huckleberry and early lowbush blueberry. Staggerbrush, dangleberry, mountain laurel, and sheep laurel also occur. Bracken fern is abundant.
Dwarf pine forests
The only trees that can recover from frequent fires are pitch pine and blackjack oak, which are abundant here. Deprived of the opportunity to grow tall, these trees grow as shrubs that may only be tall. Black huckleberry and early lowbush blueberry are again common here. Mountain laurel, sheep laurel, and bearberry are also common.
Oak-dominated forests
Without fires, leaf litter accumulates, creating an environment that favors the establishment of oak seedlings instead of pine seedlings. In time, the pines grow old, die, and are replaced by oaks. The most common are black, scarlet, chestnut, white, and post oaks. Pitch and shortleaf pines are scattered among the oaks. The forest canopy tends to be closed. The understory vegetation is similar to that of the pine-dominated forest, with black huckleberry, early lowbush blueberry, and dangleberry common.
Cedar swamp forests
Swamp forests dominated by Atlantic white cedar occur along the waterways of the pine barrens. The white cedars often grow from pools of standing water and, in contrast to the surrounding pine forests, considerably darken the understory. Amid the white cedars are red maple, sour gum, pitch pine, and sweet bay magnolia. In openings and edges grow highbush blueberry, dangleberry, swamp azalea, fetterbush, and leatherleaf. Sweet pepperbush, inkberry, and winterberry are also present.
Hardwood swamp forests
Sweet gum and red maple are the most abundant trees in the hardwood swamp forests. American holly, a broadleaf evergreen tree, is common. Pin oak, swamp white oak, willow oak, tulip tree, sour gum, and sweet bay magnolia are associates. Poison ivy and Japanese honeysuckle are often abundant and grow in thickets. Shrubs include arrowwood, spicebush, highbush blueberry, sweet pepperbush, and swamp azalea.
Grasslands
The region also contains areas of maritime grassland on Martha's Vineyard, Nantucket, and out at the tip of Long Island that are unique in the United States.