Negative Impact of Fire Suppression on Oaks

Decades of fire suppression in the southern Appalachians have had several negative effects on oak regeneration. The absence of fire since the turn of the 20th century has allowed species that are intolerant of fire to become established and grow to a size where they can now resist fire because of the thicker bark associated with age. At greater than 5 cm (2 inches) d.b.h., yellow-poplar becomes almost as fire resistant as oaks (Maslen 1989). Mockernut and pignut hickories, scarlet oak, red maple, and blackgum are examples of species that are often found on sites where fire has been long absent (Harmon 1984, Martin 1989, Van Lear and Watt 1993).

Suppression of fire has also allowed shrubby understory species to occupy drier sites where fire was once frequent and oak was more dominant. In particular, rhododendron has dramatically increased its areal extent (Van Lear and Waldrop 1989, Martin 1989). Impenetrable thickets of ericaceous species, such as rhododendron, mountain laurel, and huckleberry, now often dominate midstories and understories of hardwood stands in the southern Appalachians. They prevent desirable hardwood regeneration from becoming established (Beck 1989). Fire would top-kill these species and, although they do sprout, new growth is slow and they would likely be relatively unsuccessful competitors of regenerating oaks (Van Lear and Watt 1993).

Yellow-poplar produces an abundance of seeds almost annually and many seeds remain viable in the litter and duff layer for several years (Carvell and others 1955, Maslen 1989). Yellow-poplar seeds germinate readily after fire (Shearin and others 1972). However, in a regime of frequent fire, small yellow-poplar seedlings would be killed and the reservoir of stored seed in the duff would be gradually depleted. Thus, frequent fires would control to a large degree this major competitor of oaks on high-quality sites (Van Lear and Watt 1993).