Abstract
There is increasing recognition that plant traits contribute to variations in fire behavior and fire regime. Diversity across species in litter flammability and canopy flammability has been documented in many woody plants. Grasses, however, are often considered homogeneous fuels in which any flammability differences across species are attributable to biomass differences alone and therefore are of less ecological interest, because biomass is hugely plastic. We examined the effect of grass canopy architecture on flammability across eight grass species in short grass steppe of New Mexico and Texas. To characterize grass canopy architecture, we measured biomass density and “biomass-height ratio” (the ratio of canopy biomass above 10 cm to that of biomass below 10 cm). Indoor flammability experiments were performed on air-dried individual plants. As expected, plant biomass influenced all flammability measures. However, biomass-height ratio had additional negative effect on temperature exposure at soil surface (accumulation of mean temperature >100 °C) in well-cured grasses, which is an important fire behavior metric predicting soil heating and meristem survival. This canopy architecture effect, however, needs further investigation to be isolated from biomass density due to correlation of these two traits. This result demonstrates the potential for species-specific variation in architecture to influence local fire effects in grasses.
Highlights
Savannas, in which grasses coexist with scattered trees, are fire-dependent ecosystems: Recurrent fires suppress tree density and maintain high light environments favorable to grasses
In well-cured grasses, which is an important fire behavior metric predicting soil heating and meristem survival. This canopy architecture effect, needs further investigation to be isolated from biomass density due to correlation of these two traits
Principal component analysis indicated that the first two axes account for 87.0% of total variation in flammability metrics (Figure 2)
Summary
In which grasses coexist with scattered trees, are fire-dependent ecosystems: Recurrent fires suppress tree density and maintain high light environments favorable to grasses. Dead biomass that feeds recurrent fires, which are characterized by rapid rate of spread and short residence time [1,2]. Such fires often result in little soil heating and allow high survival of surface and below-ground grass meristems [3,4]. Such fires limit woody plants, because they can kill or top kill woody plants. Identified flammability traits include biomass, fuel moisture content, leaf dimensions, and chemical composition, and traits that characterize plant canopy architecture such as biomass density and retention of dead biomass [8,9,10,11,12,13,14,15,16]
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