8.1 INTRODUCTION

Fire has an important role in structuring ecosystems. Knowledge of the effects of fire on the ecosystems allows proper management of those ecosystems in terms of regeneration and productivity of vegetation, nutrient retention, and land/water interactions. Fires can be viewed as large-scale ecosystem experiments, but because forest fires usually occur without warning there are seldom pre-fire data, and effects are poorly understood. This is particularly true of the effect of fire on nutrient losses from watersheds. Most of the published studies were started one or two years after the fire (Wright, 1976; Nakane et al., 1983).

   Several papers have stated general hypotheses concerning the role of disturbance (usually clearcutting) in determining chemical losses from forested watersheds via streamflow (Likens et al., 1970, 1977; Johnson and Swank, 1973;Vitousek et al., 1979; Swank, 1988). There have been far fewer papers hypothesizing the effects of wildfire on stream chemistry (Tiedemann et al. , 1978; Wright, 1976). Few of these hypotheses have been tested, for seldom have watersheds been burned after they have been studied for a reference period long enough to allow conclusive examination of the effects of wildfire. Here, we review the results of other stream studies from burned watersheds and examine a few hypotheses using a 17-year data set of stream chemistry from two burned boreal forest watersheds at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada. The main fire studies reviewed here are: a wildfire in mixed coniferous-deciduous forest in northern Minnesota (Little Sioux fire) (Wright, 1976); a wildfire in Ponderosa pine/Douglas fir forest in the mountains of north-central Washington at Entiat Experimental Forest (Tiedemann et al.,1978); a wildfire in a red pine forest in the mountains of Etajima Island, Japan (Nakane et al., 1983); a clearcut and slash-burn study in a western hemlock/western red cedar/ Douglas fir forest in British Columbia (Haney fire--Feller and Kimmins,1984).