Particle Motion and the Theory of Charcoal Analysis: Source Area, Transport, Deposition, and Sampling

Abstract

Principles from particle-motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data: (1) fires within catchments of lakes often produce no record in fossil-charcoal curves and (2) periods characterized by no local fire (e.g., 20th-century fire suppression) often display as much charcoal as times when local fire was frequent. Quantitative theory on source area, transport, deposition, and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis (pollen slides for particles 5–80 μm in diameter, petrographic thin sections for particles 50–10,000 μm diameter) and charcoal diagrams. The relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods. Charcoal recorded on pollen slides is of a size that is difficult to lift, but once entrained it remains in suspension. Thin-section charcoal is lifted at relatively low wind velocities, but it is not suspended at normal surface wind speeds. Thermal buoyancy during fire lofts charcoal above the forest canopy, depending on particle size and wind speed. Pollen-slide charcoal sizes are underrepresented near the fire, because they remain in suspension and are preferentially exported from the burn area. Thin-section charcoal is convected to lower heights on average and is deposited nearby. Following fire, thin-section charcoal is redistributed locally by wind and thus may enter lakes. Because of cohesive forces and aerodynamics, more pollen-slide charcoal remains on the ground, and less enters lakes. Source areas for pollen-slide charcoal are subcontinental to global, and diagrams of pollen-slide charcoal are biased toward nonlocal charcoal. They can be used to interpret importance of fire for broad spatial and temporal scales. Thin-section charcoal represents, the catchment fire regime. Simulation models that generate charcoal during fire, mix sediments, and then sample at specified intervals indicate that (1) in the absence of sediment mixing the pollen-slide method should consistently resolve individual fires that occur with an expectation of >30–50 yr, (2) unless samples are continuous, neither method will produce useful estimates of fire frequency, and (3) even a modest amount of sediment mixing will obscure the signal.

Climate versus human-driven fire regimes in Mediterranean landscapes: the Holocene record of Lago dell’Accesa (Tuscany, Italy)

“…MacDonald et al, 1991;Tinner et al, 1998;Carcaillet et al, 2001a;Gardner and Whitlock, 2001), whereas macroscopic particles (>100-150 μm) express local (e.g. Clark, 1988;Whitlock and Millspaugh, 1996;Gavin et al, 2003b;Lynch et al, 2004;Higuera et al, 2005) as well as micro-regional fire episodes that may mainly depend on fire size and intensity (Pisaric, 2002;[Tinner et al, 2006a] and [Tinner et al, 2006b]; Peters and Higuera, 2007).…”

Paleoecological record of hurricane disturbance and forest regeneration in Nicaragua

“…Clark (1988) determined that larger charcoal particles are a more significant indication of fire, whereas microscopic charcoal is dispersed over long distances and redeposited and thus may not signify a local fire disturbance. The abundance of macroscopic charcoal suggests a distinct fire from those in Fire period 1.…”

Impregnation method for detecting annual laminations in sediment cores: An overview

“…In the use of liquid phase exchange, sediment is soaked in a container with acetone. One sample requires eight consecutive acetone baths over a period of one week, while measuring the baths specific gravity in comparison with pure acetone (Clark, 1988). In the case of vapor phase methodology, sediment is placed under acetone vapors in a dry chamber for three weeks (Camuti and McGuire, 1999).…”

“…The first method is applied on acetone dried material, in which the sediment is impregnated by acetone-resin-exchange (Clark, 1988). The acetone is progressively exchanged for a low viscosity polymer (Lamoureux, 1994; see also the appendix in Dean et al, 1999).…”

“…For example, Carboax (Renberg, 1981), Vestopal H (Altmuller, 1962;Ashley, 1973), methyl methacrilate (Palle et al, 1985;Murphy, 1986;Pusch, 1999), Crystic (Conway 1982), and LR hard white resin (Ferrow and Roots, 1989) have all been employed. The standard resins most used for sediment impregnation are Epoxy products (Martin et al, 1979;Crevello et al, 1981;Jim, 1985;Clark, 1988;Lamoureux, 1994;Francus, 1998;Kemp et al, 2001). …”