Forest floor characteristics and soil nitrogen availability on slash-burned sites in coastal British Columbia

Abstract

Organic forest floor materials were surveyed on spring and fall slash-burned sites in the Sproat Lake region of Vancouver Island 2 years after burning. Dominant organic matter types, distinguished according to morphological criteria, were sampled and incubated in the laboratory for 26 weeks with periodic leaching and measurement of mineral N. Mineralization data closely fit a first-order kinetic model. Field mineralization, estimated using mass of each organic matter type in the field and first-order model parameters corrected for local temperature, ranged from 2 to 6 g N•m−2•year−1, depending on burn severity, suggesting that slash burning did not reduce N availability below levels required to support early plantation growth, except in situations of severe burns on coarse-textured soils. Differential consumption of forest floor organic matter types increased spatial variability in N mineralization and resulted, at the most severely burned site, in 50% of mineralizable N being derived from materials covering only 5% of the site. Significant correlation between N mineralization and codes and indices of the Canadian Forest Fire Weather Index System indicated that predictions of slash-burn impacts on site fertility may be made from weather conditions prior to and during burning.