Elemental Analysis of Species Specific Forest Fire Ash: A Consideration for Soil Formation and Forest Succession in a Mixed Hardwood Forest of Northern New Jersey

Fire is a significant environmental perturbation to forests where vegetation transforms from biomass to ash, releasing stored chemical elements to soils. While much research acknowledges variation in ash composition among different vegetation types (grasses, trees, shrubs and vines), less has focused on interspecific variation among trees and the elemental influx soils receive. Therefore, this research sets out to: (1) identify major, trace, and rare earth element (REE) concentrations (n=44 elements) in ash derived from fifteen tree species, (2) determine likely elemental enrichment to soils post forest fire, and (3) assess interspecific variation in ash chemistry. A strong negative correlation existed between SiO₂ and CaO among all species (r = -.975 and p<0.0005). Additionally, ash was significantly enriched in MnO, MgO, CaO, K₂O, P₂O₅, Ni, Cu, Zn, Sr and Ba over the background soil mean, as well as in all REE’s (La through Lu) (p<0.0005 for all elements but Ni). Ash derived from Populus grandidentata, Betula lenta, and B. alleghaniensis had greatest enrichment in Zn and Ba while ash from Fraxinus americana had elevated Cu and Sr. This clearly shows significant chemical variability in ash, possibly derived from preferential element uptake by certain tree species. All REE’s were 10-15x’s greater in ash than soils, with a slight negative Eu anomaly in the ash. Little preferential uptake of any one REE exists as trees might passively sequester all these elements together, bound in mineral complexes. This research provides an important understanding of the complexities surrounding fire’s impact on critical zone biogeochemical cycling.