In the summer of 2011, I participated as a member of a field team, led by Dr. Cristina Eisenberg, on a project called “Elk, Fire, and Wolf Ecology in Aspen and Grassland Communities in Waterton Lakes National Park: A Multi-Trophic Level Landscape-Scale Study.”
Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when predators in a food web suppress the abundance or alter the behaviour of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore). Aldo Leopold is generally credited with first describing the mechanism of a trophic cascade, based on his observations of overgrazing of mountain slopes by deer after human extermination of wolves.
The majority of our field work entailed locating and measuring transects (2 x 44 m in size), using GPS and a compass, then collecting data on all of the different vegetation and aspen within those plots.
We had one close encounter with a Grizzly during our time afield. We were bush-whacking through some thick forest and one of the other field technicians heard some branches crack. After a 30 second pause, there was a prolonged, low-rumbling growl. It was estimated that the bear was 10-15 m away. We immediately left the area and walked 2 km to some open grassland. It was likely a female bear with a cub because, as Dr. Eisenberg explained, grizzlies generally “huff” rather than growl if you get too close; a growl means they are being much more assertive.