Leaf ruptures: Acoustic impulse events in wildland fires

Abstract

Quantifying wildland fires is of interest to both the fires science and land management communities. Remote sensing of these events has exclusively focused on electromagnetic spectra emissions. However, wildland fires also produce sound. Unraveling their acoustic profile will likely reveal new information unrealized through traditional remote sensing techniques. We start with the “crackling” sounds often associated with burning live vegetation. The data in these acoustic impulse events are rich, yielding information about the specific plants involved. In work presented here, acoustic impulse events are used to tease apart the influences of species, age, and plant moisture during combustion of live conifer needles. Needles were collected and burned onsite for six species within the Priest River Experimental Forest. Replicate measurements were carried out in order to reduce the influence of individual branches or trees. Moisture of the needles was ascertained just prior to the experiment through both predawn leaf water potential as well as gravimetric fuel moisture. The burning material was recorded at 50 kHz with a ½ in. measurement microphone. The acoustic impulse events were isolated and analyzed to determine likelihood of unique character traits. We present results of investigating the potential differences in acoustic signature based on species and age.

Tree crown injury from wildland fires: causes, measurement and ecological and physiological consequences

“…Field and laboratory observations indicate that there are further threshold heat fluxes above 60°C that can dramatically change the physiological function of the leaf (Jolly et␣al ., 2012 ). For example, exposure to direct flames causes radiative and convective heat fluxes with gas temperatures well above common ignition temperatures (>320°C), causing the cuticle to mechanically fail via rupturing or combusting quickly to pyrolyse and form char (Yedinak et␣al ., 2019 ). In addition, high temperatures may lethally damage the guard cells that control stomatal aperture, contributing to plant water loss (Rogers et␣al ., 1981 ).…”