A diverse number of plant species reside in the watershed as well. Red, white, and black spruce, red maple, white birch, and trembling aspen are the most common. Jack pine is commonly found in regions that fires have repeatedly ravished, while cedar is found in bogs and areas where gypsum and limestone are present. Higher altitude slopes and ridgetops house sugar maple, beech, and yellow birch trees. Zelazny et al. note that " high frequency of disturbed sites dominated by aspen stands reveals the degree of historical and recent human disturbance along the Petitcodiac River." The Petitcodiac River's riparian zone houses a number of trees, including willows, white spruce, white pine, and speckled alder. Other trees, such as the tamarack and white pine, can also be found in the watershed. Plants such as the rufous bulrush tend to grow near calcareous areas, and hemlock can be found in small, pure stands. Alien plant species include the mother-of-thyme, the Japanese barberry, the Scotch broom, the yellow flag, and Canada bluegrass.