Short-term effects of surface fire on the biomass and nutrient standing crop of Populustremuloides in southern Ontario

Abstract

The standing crop of biomass and nutrients (N, P, K, Ca, and Mg) were estimated for Populus tremuloides trunk, lateral branch twig, and foliage in a 30-year-old open stand in West Luther Township, Wellington County, Ontario. Separate estimates were made for trees in areas subjected to light surface burning (about 160 °C at the surface) and in unburned areas. Allometric relations between a variety of tree measures showed that the best estimates of standing crop were derived from simple log regressions with trunk dbh as the independent variable.The range of 7.0 to 8.9 t/ha of total aerial aspen biomass was considerably lower than other reported values and reflected both the low stand density and poor site conditions. Accumulation of tree biomass was unchanged by light surface burning. Evidently, the environmental changes were too slight to cause postfire changes in the established overstory.Distribution of nutrients within the tree components was similar to that reported elsewhere; Ca and N were the two most abundant, while P, K, and Mg accumulations were much lower. The relative importance of various tree components as nutrient accumulation sites followed the order leaves > twigs > lateral branches > trunk. The leaves were the site of the accumulation of functionally important N, P, K, and Mg whereas the trunk was the prominent site for structurally important calcium. The total accumulation of all nutrients (103.5 kg/ha) was strikingly low in comparison with amounts reported for other deciduous forests. Accumulation of nutrients in the trunk, lateral branches, and twigs was not appreciably altered by fire. Major proportions of nutrients in these components would have accumulated before burning.Amounts of nutrients contained in leaf biomass were significantly changed after burning. Concentrations in leaves from burned areas were 24–42% higher than control levels, whereas the preburn levels were similar. These substantial postburn increases in leaf nutrient levels, related to a flush of soil nutrients from ash, would have an important effect on those wildlife species utilizing the aspen as a food source.