RELATIONSHIPS BETWEEN FIRE SEVERITY AND ATMOSPHERIC AND LEACHING NUTRIENT LOSSES IN BRITISH-COLUMBIAS COASTAL WESTERN HEMLOCK ZONE FORESTS

The relationships between fire severity and fire-induced nutrient loss es to the atmosphere and through soil leaching were investigated using small (4m(2)) plots in logging slash. The study utilized (Pseudotsuga menziesii - Tsuga heterophylla - Thuja plicata) slash in southwestern British Columbia, Canada, in an area where overland flow was negligib le. Twenty-two plots containing a range of slash fuel loads were burne d, nutrient (N, P, S, K, Mg, and Ca) losses to the atmosphere were mea sured, and nutrient (N, P, K, ME, and Ca) losses in soil leachate were quantified for the first year postburn. For a given nutrient, total ( atmospheric plus leachate) fire-induced losses were similar to atmosph eric losses and could be reliably predicted from them due to the relat ively low magnitude of leaching losses; Leaching losses were generally poorly related to atmospheric losses. Total, atmospheric, and most le aching losses increased as fire severity (defined as fuel consumption) increased. Nutrient losses were better estimated from fuel consumptio n variables than they were predicted from fuel load variables. As most of the results of the study were consistent with those of studies con ducted elsewhere, these results likely apply to a wider geographic are a and range of fire situations than those of the present study. The ef fort and cost of assessing total fire-induced losses in, at least, Nor th American conifer forests can be minimized, without sacrificing much accuracy, by not measuring fire-induced soil leaching losses, but ass uming these are 5-20 kg/ha, depending on the nutrient and the severity of the fire. If nutrient leaching into water bodies is to be quantifi ed, then measurement of leaching losses would be necessary.