PS 72-139
You “rot” my world: How decomposition influences litter flammability
Fire is a powerful ecological phenomenon shaping vegetation distribution and structure across many biomes. Plants have the ability to influence the nature of fire through differences in their traits, but elucidating the specific traits that influence flammability, and determining the nature of that influence has yet to be accomplished. Leaf size, by influencing litter density, has strong effects on flammability: large leaves lead to less dense and more flammable litter. Decomposition, by changing the leaf particle size through time, will alter bulk density and thus influence fire behavior. However, past studies of decomposition rate have measured only mass loss and no work as yet addressed particle size. This study was conducted in the mixed-conifer forest of Sequoia and Kings Canyon National Parks, California, USA. Leaf litter was collected during summer 2012 from eight tree species (Abies concolor, Abies magnifica, Calocedrus decurrens, Pinus jeffreyii, Pinus lambertiana, Pinus ponderosa, Quercus kelloggii, and Sequoiadendron giganteum) representative of this system. Samples were placed in litter bags at 6 locations (3 altitudes and 2 aspects), and left to decompose for 1 and 2 years.
Results/Conclusions
Preliminary results for this study look at the particle size change from initial samples to samples after one year of decomposition. Using the mean particle size of undecomposed litter and transforming the data due to its non-linearity, I developed a model for how spread rate changes with particle size. I use spread rate because it is a known component of fire behaviour. I then applied this relationship to the data obtained from the one year decomposition study to predict spread rate. This allowed me to predict change in spread rate for all 8 species, but also to determine if there was a change in species ranking. The data obtained show a significant decrease of spread rate for all species, and only the pines remain flammable. In terms of species ranking, there is only an inversion between Pinus ponderosa and P. lambertiana, with the later becoming significantly less flammable. These results show the influence of decomposition on flammability and the potential for some species to influence the fire environment. This work represents a novel contribution to the decomposition field and constitutes a first step in linking decomposition rate and flammability in litter driven systems.