There has been increasing attention to plant trait variation as a contributor to variation in fire behavior and fire regime. Variation across species in litter flammability and canopy flammability have been documented in many woody plants. Grasses, however, are often considered as homogeneous fuels in which any flammability differences across species are attributable to biomass differences alone and therefore of less ecological interest because biomass is hugely plastic. Recently, studies found some evidence showing that additional traits such as leaf surface area to volume ratio and canopy architecture traits also influence flammability. However, canopy architecture has only been examined on partial plant canopies. We examined effect of two canopy architecture traits on grass flammability at individual plant level by asking two questions: 1) how does total biomass influence each flammability measurement? 2) How does canopy architecture influence flammability after we account for effect of total biomass? We sampled eight grass species of short grass steppe and mixed grassland of eastern New Mexico and Texas. To characterize canopy architecture, we measured biomass density and biomass ratio (the ratio of biomass above 10 cm to biomass below 10 cm relative to ground). In-door flammability experiments were performed on air-dried individual plants.
Results/Conclusions
As expected, plant biomass was the first order control of flammability measures. However, biomass density had an additional positive effect on temperature integration above 100 °C near ground, which is an important fire behavior metric predicting soil heating and meristem survival. In addition, biomass ratio negatively influenced canopy heating, which may affect fire response of coexisting woody species at a fine scale by altering the severity of canopy scorch and bole heating. These results demonstrate the potential for species-specific variation in architecture to influence local fire effects in grasses, despite broad scale fire behavior being largely driven by fuel load alone. Grass fueled fires are believed to be one of the important disturbances to maintain savannas by suppressing tree cover. However, understanding of this process is not complete because related studies tend to treat grasses as homogenous fuels, which can lead to misunderstanding if dominant species vary in flammability traits.