Understanding historic fire regimes to develop benchmarks for emulating historic natural disturbance processes in the interest of conserving biodiversity has been actively pursued for approximately 30 years. Mixed-severity fire regimes are increasingly becoming a recognized component of historic fire regimes. Mixed-severity fire regimes are inherently difficult to classify and characterize given the complexity of the process and the multiple scales at which this complexity is expressed. I utilized a systematic study design to gather fire scar and stand dynamic information in order to describe and classify the historic fire regime. I established the presence of mixed disturbance regime dominated by a mixed-severity fire regime. The historic fire regime was mixed-severity over time dominated by individual high severity fire events occurring at a frequency of 60-130 years with some areas that experienced lower severity fire events occurring at a frequency of 20 - 40 years. Twenty-one per cent of the current landscape was dominated by high-severity fire, 42% by mixed-severity and 37% had an unknown fire history. I developed a fire regime classification scheme that provides a useful tool for considering fire severity in mixed-severity system with forest species that generate strong establishment cohorts. I was able to combine time-since-fire methods with a systematic study design and this combination provided an excellent tool to explore mixed-severity fire characteristics in a complicated mixed-disturbance forest. I found limited relationships between topographic controls and fire severity. I found a number of significant relationships that fit the broadly held perceptions of how fire severity would affect species relative densities and stand structure attributes. The existing stand origin map and the Vegetation Resource Inventory stand age were largely accurate for high-severity 20th century fires but had decreasing accuracy in older forests and for mixed and unknown fire severity. The accuracy of the Vegetation Resource Inventory leading species accuracy was quantified at only 60%. My results have implications for fire and forest management in south-eastern British Columbia and in other forest systems that had historic mixed-severity fire regimes with tree species that have strong establishment cohorts. / Graduate / 0478 / 0329 / rick.kubian@pc.gc.ca

Management of natural landscapes requires knowledge of key disturbance processes and their effects. Fire and forest histories provide valuable insight into how fire and vegetation varied and interacted in the past. I constructed multi-century fire chronologies for 10 sites on six mountain ranges representative of the eastern Great Basin (USA), a region in which historic fire information was lacking. I also constructed tree recruitment chronologies for two sites. I use these chronologies to address three research foci. First, using fire-scar data from four heterogeneous sites, I assert that mean fire interval (MFI) values calculated from composite chronologies provide suitable estimates of point MFI (PMFI) when sample area size is ≈&frac; ha. I also suggest that MFI values for single trees can be used to estimate PMFI after applying a correction factor. Next, I infer climate effects on regional fire patterns using 10 site chronologies and tree-ring-based indices of drought and of El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation ([PDO), Pacific Ocean surface temperature variability known to affect North American climate. Regional fire years (≥33% of recording sites) were synchronized by wet-dry cycles where the probability of occurrence was highest in the first year of drought following a wet phase and lowest when climate conditions transitioned from dry to wet. Regional fire probability was highest when ENSO and PDO were negative (Southwest pattern). Local fire years occurred under a broad range of conditions. Fire seasonality was bimodal with early and late-season fires dominant. I imply that Native American burning practices were responsible for differences in historic and modern fire seasonality. Lastly, I assess fire regime and tree recruitment variability within two fire-sheds. PMFI varied more than 10-fold within each site. A mixed-severity regime was dominant. A majority (>60%) of fires were small (<10 ha) but together accounted for a minor proportion of area burned. Recruitment pulses varied spatially from stand to landscape-scales and were often synchronous with multi-decade, fire-quiescent periods. I recommend that management strategies employ fire and fire-surrogate treatments to restore disturbance processes to these and similar landscapes at spatial and temporal scales consistent with the historic record.