Document: DYL-3-68-36

Flammability as niche construction: Canopy architecture's effect on the flammability of a chaparral species.

SCHWILK, D.W.*

Stanford University, Stanford, CA 94305 USA ¹

Abstract:
The observation that some plants depend upon regular wildfire for their continued persistence and that many of these plants are quite flammable has prompted suggestion that such plants might have evolved characteristics that enhance flammability and thereby prevent the invasion of less flammable, fire-sensitive species. Although attractive to ecologists of fire-prone systems, this hypothesis has received a good deal of criticism on the grounds that it was group selectionist. Flammability traits may, however, influence evolutionary trajectories through their effect on the local environment. By affecting local fire intensities or the probability of ignition, traits that change flammability may indirectly influence selection on fire-related life history and physiological traits. Flammability's potential niche construction effects depend upon the ability of plant traits to modify the environment in a manner that influences selective pressures. The retention of dead branches in the canopy has been cited as contributing to the flammability of some chaparral shrub species and chaparral species differ dramatically from one another in the degree to which they retain dead branches. No experiment, however, has demonstrated that differences in plant canopy architecture on the scale of observed variation in nature can affect local fire intensities. I experimentally manipulated shrub canopy architectures of Adenostoma fasciculatum, a non self-pruning shrub, to mimic self-pruning in four small scale (4 by 6m) treatments: Removal of all canopy dead wood, clipping of all dead wood with wood left as litter, control, and dead wood addition. Seven replicate plots of each treatment were burned in two controlled burns on November 12, 1999. Peak fire temperatures and heat release were significantly lower in the clipping treatments than in the control or wood addition treatments, demonstrating a significant local effect of simulated self-pruning. Dead wood removal and clipping only treatments did not differ significantly, suggesting that the observed effect is a result of canopy architecture rather than of differences in total fuel load.

Keywords: Chaparral, flammability, Mutch Hypothesis, niche construction

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.