Background
The North American distribution of Grizzly bears (Ursus arctos) has been significantly reduced since the emergence of European settlers (Fig. 1). Today, grizzlies primarily occupy remote mountainous locations or protected areas where human related mortality and habitat loss is less pronounced. Maintaining viable populations at the periphery of their distribution has been a management challenge as grizzlies in these location are typically vulnerable to human-caused mortality, genetic isolation, and habitat loss (Paetkau et al., 1998; Proctor et al., 2002). Currently this is the situation at the eastern edge of their distribution in the Rocky Mountains and foothill regions of Alberta, and as a result, grizzlies were classified as a threatened species in 2010 (ASRD 2010). Even in protected areas such as Banff National Park, human caused fatality remains the largest single mortality factor (Benn and Herrero, 2002; Garshelis et al., 2005), while limitations in productive habitat have contributed to the lowest reproductive capability of any studied grizzly population in the world (Garshelis et al., 2005). The effects of human-caused mortality and slow reproduction have contributed to a negative population growth rate of Banff grizzlies (Sawaya et al. 2012). Completely mitigating human caused mortality has proven to be a significant challenge to Parks Canada because bears frequently select valley bottom riparian and edge habitats (Theberge, 2002), where human development and use also occur. Reducing human caused mortality has been a priority in Banff for over 20 years and improvements in waste management, public education, highway fencing and other practices have been successful at reducing mortality. Unfortunately, these efforts only influence “top down” population effects and have little, or even negative effects, on “bottom up” parameters. With Banff having the lowest reproductive capacity of any grizzly bear population studied, it is imperative to establish or enhance productive habitat to generate positive population growth. Furthermore, if productive habitat can be established distant to human use locations, mortality may decrease as bears select these locations away from human infrastructure and use.
Why Prescribed Fire?
Primary grizzly habitat in the Rockies generally occurs in a mosaic of early seral stage forests and natural openings in the absence of human interactions (Hamer and Hererro 1987; Nielsen et al., 2006). Post-disturbance locations such as clear cuts and burns often generate productive bear habitat (Zager et al.,1983; Nielsen et al., 2004 ), however, if they are associated with human access they can become mortality sinks (Nielsen et al., 2006). Throughout Banff National Park, forest disturbances were significantly reduced throughout the 20th century as forest harvest was eliminated and fire suppression became extremely effective (White 1985). In the absence of these disturbances the majority of the forest ecosystems have developed into mature even age stands (Fig. 2) that don’t typically support productive growth of grizzly bear food resources. In the early 1980’s, prescribed fire was first introduced as a forest management tool in Banff as a means to restore and maintain ecological structure and function (White 1985). The prescribed fire program in Banff has evolved substantially over the last 30 years, and over 25,000 hectares have been burnt to support a variety of management objectives. Prescribed fire appears to be the most appropriate application for restoring grizzly bear habitat because: 1) it mimics the natural disturbance agent to which grizzlies evolved 2) it can be applied in remote areas without introducing human access 3) research has documented post-fire selection by grizzlies (Zager et el.,1983; Hamer and Herrero, 1987). Furthermore, today’s understanding of prescribed fire as a management tool makes it a safe and cost effective application. Currently we are, however, challenged with understanding the multitude of variables of fire prescriptions that contribute to most effectively enhancing grizzly bear habitat.
Research Objectives
1) To compare the occurrence, distribution and productivity of 16 known grizzly bear foods in prescribed fires to adjacent non-disturbed forest stands. This will allow us to understand which food sources are promoted by fire and to quantify by how much.
2) To evaluate prescribed fire variables (fire severity, fire intensity, timing of fire, and time since fire), topographic variables (elevation, aspect and terrain wetness), and forest stand variables (canopy cover and species composition) to understand how they contribute to productive grizzly bear habitat in post-fire environments.
Expected Results
Although there is limited research examining grizzly bear foods in prescribed or wildfires, research in non fire disturbances including clearcuts (Nielsen et al., 2004) and roadsides (Roever et al. 2008) indicate that insects, roots and most herbaceous food items generally increase whereas many fruiting species generally decrease in abundance but increase in fruit yield. It is expected that these same species will be positively associated with prescribed fire sites.
It is difficult to predict the influence of fire variables on the bear food enhancement, although, it can be expected that more severe and intense fires (typically during summer and fall) will delay the climax of bear food productivity whereas less severe and intense fires (typically during spring) will result in quicker establishment of bear foods.