Small-scale fire temperature patterns in upland Quercus communities.

Abstract

Two upland second-growth Quercus alba sites in the Land Between The Lakes National Recreation Area in Kentucky and Tennessee were prescribed burned during the dormant season of 1993-94 to assess small-scale spatial effects of fire on forest community structure. Controlled burning is used as a tool for maintaining Quercus communities and preventing succession to communities dominated by mesophytic species such as Acer saccharum in this region. In this study, one of the sites had both overstorey and understorey dominated by Q. alba, while the other had the understorey dominated by mesophytic species (mainly A. saccharum). Fuel data were obtained prior to burning, fire temperatures at 3 heights were taken during the fire, and microtopographic and vegetation data were collected following the burn. Spatial analysis and pattern analysis were employed to examine fire temperature patterns in relation to microtopography and fuels, and fire temperature effects on vegetation. Fire temperatures at the surface, and 33 and 75 cm above surface were light to moderate ranging from 52 to 260°C. These light temperature fires probably have no adverse effect on nitrogen in the system, but also have little effect on vegetation composition. Fire temperature patterns were affected by litter duff biomass when slope steepness was low (i.e. slope <20 ). Steeper slopes had a stronger effect on fire temperature patterns, thereby masking the influence of fuel biomass. Thus, the direct and indirect effects of topography on fire behaviour may be more important than fuel loading when assessing the effects of prescribed burns in eastern deciduous upland forests. Areas previously burned (2 yr before this study) had similar fire patterns to previously unburned areas. However, fire severity was greatest in the previously burned areas. Thus, the influence of fire on vegetation may have cumulative effects. The spatial structure of the prescribed burn influenced the patterns of vegetation response. However, all species sprouted indicating an insignificant effect of fire on vegetation composition. Different sampling designs may be required for assessing fire phenomena as slope steepness varies. For example, sampling quadrats may need to be closer together on level terrain than on sites with slopes >20. In addition, independent samples must be further apart to assess accurately the effects of fire at varying distances above the soil surface, in comparison to distances between samples assessing surface fire effects.

Key words

• burning
• control
• controlled burning
• cultural control
• deciduous forests
• fire effects
• forest trees
• forests
• fuels
• natural regeneration
• patterns
• plant succession
• sampling
• secondary forests
• slopes
• spatial variation
• species diversity
• temperature
• topography
• trees
• upland areas
• vegetation management
• vegetation types
• weeds
• woody plants
• woody weeds