Historic Fire Regimes of Grassy and Heath Balds

Grassy Balds

The fire regime of grassy mountain balds within the historic period is much better understood than the prehistoric fire regime. Grazing in the historic period has heavily influenced both the flora and structure of grassy mountain balds. Cattle and sheep were the most common and important grazers on grassy balds from the early to mid 1800’s to early 1900’s (White and Sutter 1999, Smathers 1981). In fact, grazing intensity was enough to reduce the vegetation to a “low grassy sward” (Lindsay and Bratton 1979), which provided very little fuel to carry fires. During the historic period when grazing was common, fires on grassy balds were not common (Lindsey and Bratton 1979).

Grassy Bald Formation

It is possible that fires have played a role in bald formation and subsequent maintenance prior to the introduction of non-native grazers but it is far from certain. Hypotheses regarding bald formation are numerous and include human origin in the historic period, geologic origins, climatic events in relation to topographic position, disturbances including wind and ice storms, insect outbreaks, chronic grazing (by now extinct native grazers) and fires, both catastrophic fire and frequent prehistoric anthropogenic fire (see White and Sutter 1999 or Peterson 1981 for discussions of various bald formation hypotheses).

Central to the debate over bald formation is when balds were formed. It is certain that some balds originated or were enlarged during the historic period when high mountain tops were used by settlers for summer pasture (Lindsay and Bratton 1979). Creation and expansion of balds in the historic period likely involved some use of fire in conjunction with girdling and felling of trees (Lindsay and Bratton 1979).

Though the earliest European explorers failed to mention balds (Smathers 1981, Peterson 1981), it seems likely that some balds were in existence prior to European arrival (see White and Sutter 1999). The first mention of balds per se post-dates the beginnings of European settlement of the mountains, but not by many years (Smathers 1981). However, “savannas”, “pasture” and “prairies” are mentioned by early explorers of the region.  Some of these may have been an interpretation of what is known as, or what have become bald communities today (Peterson 1981). Other evidence that suggests balds did exist in some form prior to European settlement include bald formation myths within Cherokee culture (Smathers 1981), and deep and well developed soil characteristics of some grassy balds which was interpreted as an indication that they pre-dated the arrival of people of European ancestry (Cain 1931).

One mechanism proposed for the formation of balds that were in existence prior to settlement by Europeans involves catastrophic fire following another disturbance.  It is possible that severe fires following windthrow, insect outbreak or another such disturbance could have created open conditions that subsequently became known as ‘balds’. Some areas in the Balsam mountains that generally resemble balds and that share many of the same species were created when severe fires burned through logging slash on former spruce fir forests in the 1920’s then again in the 1940’s (Barden 1978).   However, recent burn scars, though they share some species, do not resemble balds with respect to composition of plant species (Lindsay and Bratton 1979). Consumption of organic soils and soil erosion following severe fires may play a role in establishment of herbaceous plants rather than woody plants following the fire (White and Sutter 1999). 

Grassy Bald Maintenance

It is unlikely that lightning fires were responsible for the maintenance of grassy balds. Fire frequencies in the Appalachians are low (6 fires/year/ 1 million acres) compared to fire frequencies in the southeast and west (20+fires/year/ 1 million acres) (Barden and Woods 1974). Another estimate of lightning started fires based on historic period records is 1 fire/10 years/10,000 ha (Barden 1978). The author further states that most of those fires are of low intensity and not likely to affect woody plant encroachment and gives a rough estimate of natural fires of great enough intensity to top-kill shrubs at 1 fire in 100-200 years. Thus, natural fires (lightning caused) would not be frequent enough to deter woody plant encroachment and to maintain grassy balds as such.

If balds were in existence prior to the arrival of non-native grazers, then the most plausible explanations for bald maintenance are the influence of native grazers (possibly in conjunction with fires set by Native Americans).  We know that balds of today are an artifact of grazing by domesticated animals. Open areas (i.e., orchard-like forests with herbaceous understories) along ridge tops may have existed, which because native grazers have been extirpated and because natural and anthropogenic fires were suppressed may have become another community type. Orchard-type forests are currently in existence in the Balsam Mountains and result from periodic prescribed fire (Lindsay and Bratton 1979). Gersmehl (1970 from Pittillo 1981) classified some mountains as “nominal balds”. This is a forested mountain with “bald” in its place name, but for which there is no evidence that it was ever treeless. The soils of several such forested “balds” were studied to determine if shifts in vegetation (from grassland to forested condition) had occurred on those sites. No evidence for a shift in vegetation was found. One curious finding regarding evidence of fire on these nominal balds is the charcoal content in nominal bald soils is higher than in soils of representative forest types nearby studied balds (Knoepp et al. 1998). At bald sites charcoal was found up to 20 cm deep (Knoepp et al. 1998). Soil between 37 and 48 cm deep was carbon dated at 4945 years before present. This evidence suggests periodic burning of nominal balds occurred at a frequency higher than that of the other forest types at some time in the past.

Based on these data, lightning fire was clearly not responsible for maintenance of grassy balds, if they existed prior to settlement by Europeans. It is possible that fires set by native Americans maintained open grassy woodlands alone or in conjunction with native herbivores (woodland bison, and elk and prior to that herbivorous Pleistocene megafauna) (White and Sutter 1999).

Heath Balds

The origin of heath balds is unknown. One hypothesis regarding the formation of heath balds is that they are a climax community that develop on moderate to high elevation, xeric sites (Whittaker 1956 in White et al. 2001). There is little evidence to support this hypothesis. In fact far fewer heath balds exist than seemingly appropriate sites (White et al. 2001).  Another theory proposed by Cain (1930) is that shrub balds form after a canopy removing disturbance (such as logging, fire, insect outbreaks or windstorm) on sites where shrub thickets are already established in the understory.  Once the canopy is removed, shrubs quickly become dominant and suppress further tree seeding establishment within the thicket, creating a stable shrub-dominated community even in the absence of disturbance. Indeed, as the forestry community has recognized, rhododendron and laurel thickets are known to suppress tree regeneration and much effort is put into suppressing these thickets prior to reforestation efforts (Romancier 1971, Hooper 1969). Evidence that supports the role of fire and other canopy removing disturbances in the creation of heath balds includes a study of environmental gradients and factors correlated with the occurrence of heath balds within the Appalachian landscape.  Among other factors (including upper slopes, high elevation, convex topography, highly acidic rock types) shrub balds were found in a higher frequency than a random distribution would suggest on burned sites (White et al. 2001).

The natural fire frequency of established heath balds is not known, but lighting started fires were not and are not frequent in the Appalachians when compared to the coastal plain. Heath bald shrubs are resistant to fire and heath balds persist even when fires are as frequent as three fires in ten years (Cain 1930).