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1994 Proceedings
North American Conference on Savannas and Barrens


Matthew S. Russell, Graduate Research Assistant
and Jeffrey O. Dawson, Professor
Department of Forestry
University of Illinois - W-503 Turner Hall
1103 S. Goodwin
Urbana, IL 61801.

Living in the Edge: 1994 Midwest Oak Savanna Conferences

Fire is an integral component of change in many types of ecosystems.. Past studies of the specific effects of fire on trees have focused mainly on coniferous forest species in regions with high frequency of natural fires (Hare 1965; Kayll 1963; Gill and Ashton 1968; Vines 1968; Martin and Christ 1968). Most of this research has been conducted to determine heat limits tolerable in prescribed or natural fires.

In eastern North America, fire has been implicated as a factor in maintaining oak savannas which were commonly intermixed with presettlement tallgrass prairie (Abrams 1992). Upon settlement and transformation of land to urban and agricultural uses, fires occurred with decreased frequency and intensity. However, exclusion of fire from post-settlement lands has been implicated in the gradual replacement of dominant early to mid-successional Quercus species with late-successional, more shade tolerant Acer species (Wuenscher and Valiunas 1967; Reich et al. 1990). Pallardy et al. (1991) noted significant changes in species composition over a 22 year period for three distinct forest types in Missouri. Increases in the prevalence of sugar maple (Acer saccharum) and decreases in Quercus spp. were attributed to exclusion of fire and succession. The continuing trend toward late successional stages has led many resource managers to reconsider fire as a management tool to control forest composition.

The consensus among many researchers is that the vascular cambium of trees will be killed at temperatures exceeding 60o C (Hare 1961). Recent studies by Hengst and Dawson (1994) indicate that bark thickness and thermal conductivity influence moderation of cambial temperature increases resulting from artificial burning of several species native to the oak-hickory association of the eastern United States Bark has long been recognized as a factor which affords fire resistance to trees (Starker 1934; Hare 1965; Martin and Christ1968; Vines 1968). Numerous air-filled cells in bark provide insulation and prevent rapid fluctuation of temperatures at the vascular cambium. Martin (1968) conducted laboratory experiments examining the thermal conductivity of the bark of several species. His results demonstrated the good insulating qualities of bark and identified some factors contributing to variation in heat conductance among the bark of different species.

Density is a factor which affects thermal characteristics of various bark types (Martin and Christ 1968). There is a positive correlation between bark density and thermal conductivity. A trend towards higher bark density for thin barked species of the central hardwood region was observed by Hengst and Dawson (1994). This observation coincided with greater thermal conductance and higher peak cambial temperatures. When a heat source is applied to the bark surface, fluctuation of temperature varies with bark thickness. Cambial temperatures have been observed to continue to rise after heat sources were removed in simulated fires (Vines 1968; Kayll 1963; Hengst and Dawson 1994). Thick-barked species require longer times to reach peak temperature and return to ambient conditions. Thin-barked species peak higher and earlier than thin barked species and start to cool as soon as the heat source is removed. The objectives of this study were to determine the effects of a simulated burn on cambial mortality and subsequent wound wood production one year after an artificial burn conducted by Hengst and Dawson (1994).


Study trees were located in the Illini Forest Plantations (40o04 No Lat. 88o12 Wo Long.) in Urbana, Illinois. The plantation contains hardwood and soft