Temperature and source material influence ecological attributes of ponderosa pine and Douglas-fir charcoal

Charcoal has numerous physical and chemical properties that allow it to influence a variety of ecological processes. The objective of this study was to evaluate how several ecological properties of charcoal vary as a function of formation temperature and the source of woody material from which it is formed in ponderosa pine/Douglas-fir (Pinus ponderosa/Psuedotsuga menziesii) ecosystems. We generated charcoal in the laboratory at two temperatures (350 and 800 °C) and from four source materials (bark and wood from mature Douglas-fir and ponderosa pine trees), collected in western Montana. In an incubation experiment, where soils were amended with charcoal and glycine, all charcoal types resulted in higher rates of net ammonification relative to the no-charcoal control, and all charcoal types (except 800 °C ponderosa pine bark) increased net nitrification rates relative to the control. All charcoal types were also effective at sorbing catechin (±), an allelochemical produced by the invasive species Centaurea maculosa; however, higher temperature charcoals had a higher sorption capacity. High temperature charcoals also demonstrated higher extractable NO3−, pH, electrical conductivity, total C content; whereas, soluble and total phenol concentrations, extractable PO43− and NH4+, and density were lower in high temperature char relative to low-temperature charcoal. The species (ponderosa pine or Douglas-fir) and material (wood or bark) from which charcoal formed also resulted in variation in several properties; however, this variation was of minor importance relative to differences caused by temperature, and thus is likely a less significant source of variation in natural systems. These data suggest that charring temperature, which may be correlated with fire severity during fire events, is likely the greatest source of variability in these charcoal properties in the ponderosa pine/Douglas-fir ecosystem.