Relationships Between Fuel Properties and Slashburning-Induced Nutrient Losses

Abstract

Abstract The relationships between slash load, slash and forest floor consumption variables, and species origin of slash (slash type), and nutrient (N, P, S, K, Na, Mg, and Ca) losses to the atmosphere during slashburning, were studied by burning 50 plots, each 2.25m² in area. The plots contained known amounts of slash materials derived from four major southwestern British Columbia tree species (Tsuga heterophylla, Thuja plicata, Chamaecyparis nootkatensis, and Pseudotsuga menziesii) and were burned under different fire weather conditions. Nutrient losses (g/m²) decreased in the order: N > Ca > S > K > Mg > P > Na and were generally within the range of such losses recorded for operational prescribed burns in western North America. Losses of all nutrients except Na were positively correlated with fuel consumption. Nitrogen and S exhibited the best correlations, whereas no correlations were found for Na. Of the fuel consumption variables considered, depth of forest floor consumed, then total slash consumption, were best correlated with nutrient loss. Losses (g/m²) of most nutrients generally increased with slash load and as slash type changed from Tsuga, to Pseudotsuga to Thuja/Chamaecyparis. This was partly due to the effects of slash load and slash type on fuel consumption, and partly due to their effects on burning-caused changes in nutrient concentrations in slash materials. The study suggests that nutrient losses to the atmosphere during operational slashburns can be minimized by minimizing forest floor and large diameter slash consumption during burning. For. Sci. 34(4):998-1015.