Effects of Fire on Northern Hardwood Vegetation and Wildlife

Northern hardwood forests are a fire-sensitive community-type.  Fire resistance of trees depends mainly on thickness and insulating abilities of their bark as well as their diameter and how the bark thickness tapers along the bole (Harmon 1984). Thin bark makes practically all the major tree species in northern hardwood forests very susceptible to fire injury. The cambium of black cherry, for example, reaches lethal temperatures faster than in any other eastern hardwood species, and the cambium of sugar maple may be injured even without external damage (Uchytil 1991; Coladonato 1991).  Fire can easily damage the shallow roots of basswoods and usually top-kills American beech (Sullivan 1994a; Coladonato 1991), so even occasional or light fires can have dramatic impacts.

Beech, black cherry and basswood regenerate by root suckering or stump sprouting (Coladonato 1991; Sullivan 1994a, Uchytil 1991), but yellow birch and sugar maple are poor sprouters after fire and depend on wind-dispersed seeds. However, yellow birch is likely to be a part of the post-fire regeneration in northern hardwoods, since fire seems to enhance its seed germination and seedling establishment (Sullivan 1994b; Timenstein 1991). While light surface fires may favor sugar maple seedlings over basswood, hotter fires destroy sugar maple reproduction providing the necessary light gaps for basswood (Sullivan 1994a).

Since even light fires may damage thin-barked northern hardwoods, fire usually opens up the canopy. Trees not instantly killed but having suffered fire damage are more susceptible to decaying fungi that can cause delayed mortality (Sullivan 1994a; Colodonato 1991). Such open woodlands with sugar maple, beech and birches provide ideal habitat for the yellow-bellied sapsucker. Ruffed grouse, vireo and black-throated blue warbler, however, benefit from prolific resprouting that provides a dense shrubby understory (Chris Kelly, personal communication).

Repeated or intense fires can change moisture conditions and convert a mesic site into a more xeric one, thus promoting oak rather than northern hardwood species (Van Lear & Watt 1993). In fact, widespread, centuries-long Native American burning practices most likely influenced the establishment and stabilization of oak-pine communities in the Appalachians even on mesic sites (Brose et al. 2001). Charcoal studies suggest that fires set by Late Archaic and Woodland peoples increased populations of fire-tolerant oaks, chestnut and pines in Kentucky and support the theory of Indian burning playing a role in the transition from northern hardwoods to white pine-oak forests in Ontario, Canada (Delcourt et al. 1998; Clark & Royall 1995).